2004 Publications

on or concerning rotifers

The effects of drying and rewetting on rotifer egg bank hatching were examined for three habitats in a mainstem reservoir embayment, Kentucky Lake, KY: a littoral zone with an annual drying and wetting cycle, a floodplain that was only rarely inundated, and a permanently wetted embayment. Hatching from surface sediments also was compared with hatching from sediments 4-10 cm and 14-20 cm deep. Seven rotifer species normally associated with littoral zones and two other zooplankton species hatched from sediments following rewetting. No pelagic species hatched. Surface sediments normally experiencing drying and rewetting cycles had a greater number of species than permanently wetted sediments. Eggs hatched more quickly from deeper than surface sediments. Results demonstrated that reservoir water level fluctuations may play a role in rotifer community dynamics by providing favorable conditions for littoral as well as pelagic species.

Although long-branch attraction (LBA) is frequently cited as the cause of anomalous phylogenetic groupings, few examples of LBA involving real sequence data are known. We have found several cases of probable LBA by analyzing subsamples from an alignment of 18S rDNA sequences for 133 metazoans. In one example, maximum parsimony analysis of sequences from two rotifers, a ctenophore, and a polychaete annelid resulted in strong support for a tree grouping two long-branch taxa (a rotifer and the ctenophore). Maximum-likelihood analysis of the same sequences yielded strong support for a more biologically reasonable rotifer monophyly tree. Attempts to break up long branches for problematic subsamples through increased taxon sampling reduced, but did not eliminate, LBA problems. Exhaustive analyses of all quartets for a subset of 50 sequences were performed in order to compare the performance of maximum likelihood, equal-weights parsimony, and two additional variants of parsimony; these methods do differ substantially in their rates of failure to recover trees consistent with well established, but highly unresolved phylogenies. Power analyses using simulations suggest that some incorrect inferences by maximum parsimony are due to statistical inconsistency and that when estimates of central branch lengths for certain quartets are very low, maximum-likelihood analyses have difficulty recovering accepted phylogenies even with large amounts of data. These examples demonstrate that LBA problems can occur in real data sets, and they provide an opportunity to investigate causes of incorrect inferences.

This paper reports the positional distribution of fatty acids in triacyl-sn-glycerols (TAG) of rotifers Brachionus plicatilis enriched with marine oils TAG. The rotifers were enriched with fish and seal oils TAG for 4-24 h, and TAG isolated from the enriched rotifers were subjected to stereospecific analysis in order to determine the content of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in the sn-1, sn-2 and sn-3 positions of the TAG. In rotifers enriched with fish oil TAG, DHA was esterified in the three positions of TAG with the distribution patterns of sn-2 (highest)>sn-3>sn-1 (lowest) positions (4- and 8-h enrichments), sn-2sn-3>sn-1 positions (12- and 18-h enrichments) and sn-3>sn-2>sn-1 positions (24-h enrichment). In rotifers enriched with seal oil TAG, DHA showed a consistent pattern of sn-3>sn-1>sn-2 positions (4-24 h). EPA in the 24-h enriched rotifers showed the patterns of sn-3>sn-2sn-1 positions (fish oil TAG enrichment) and sn-3>sn-1>sn-2 positions (seal oil TAG enrichment). In the seal oil TAG enrichment, distribution patterns of DHA and EPA were similar between the dietary TAG and rotifers TAG. In contrast, distribution patterns of these fatty acids in the fish oil TAG (sn-2>sn-3>sn-1 positions) were not entirely held in the enriched rotifers.

The possibility of applying main AOP techniques, namely ozonation, H2O2/UV photolysis and TiO2 photocatalysis to provide a significant reduction of toxicity of pharmaceutical mixtures has been evaluated. For the preparation of the mixture six pharmaceuticals were chosen among those found at highest concentrations in Sewage Treatment Plant effluents, namely carbamazepine, clofibric acid, diclofenac, sulfamethoxazole, ofloxacin and propranolol. The blue-green alga Synechococcus leopoliensis and the rotifer Brachyonus calyciflorus were utilised to assess the toxicity of the mixtures after AOP treatments. All the toxicity tests were performed using chronic standardized bioassays. The best results were obtained with ozonation. With this type of treatment a complete removal of mixture toxicity on S. leopolensis was obtained even after the shortest time of application (1 min). The ozonation treatment leads also to removal of all the pharmaceutical mixture toxicity on B. calyciflorus, by applying the oxidizing agent for at least for 2 minutes.

A numerical simulation for the dynamics of a model that describes the sexual phase of Monogonont Rotifera reproduction is presented. The simulation is carried out by means of a numerical method based on the integration along the characteristic curves. The numerical experiments cover two basic situations: the existence of an asymptotic stable equilibrium state and the existence of an stable periodic solution. Our results are in agreement with the theoretical analysis made by Calsina and Ripoll (J. Math. Biol. 45 (2002) 22).Original Abstract: Les rotiferes monogontes sont de petits animaux invertebres qui vivent dans les milieux aquatiques. Ces especes de rotiferes comprennent des males et des femelles et leur cycle de reproduction, appele parthenogenese cyclique, qui constitue une combinaison de reproduction sexuelle et asexuelle (deux phases), presente un interet considerable et fournit un modele valable pour l'etude de l'allocation sexuelle. Nous presentons dans cet article une recherche numerique de la solution du modele qui decrit la dynamique de la phase sexuelle des rotiferes monogontes, realisee a l'aide de differentes valeurs des parametres et de conditions initiales distinctes. Nous considerons a la fois les cas des equilibres stable et instable. De plus, dans le cas de l'equilibre instable, nous etudions l'evolution vers le cycle limite (stable). Par ailleurs, nous obtenons la distribution de densite pour l'equilibre stable ainsi que pour differentes etapes du cycle limite.

Rotifers were collected in the open water of twenty-eight locations (3 rivers, 12 connected lagoons and 13 isolated lagoons) of the upper Parana River floodplain during the high water (February) and low water (August) period of 2001. Greatest species richness was found in rivers during the high water period. Isolated lagoons had the lowest species richness. Abundance was highest in connected lagoons followed by isolated lagoons and then rivers, but did not show marked spatial or temporal variation. Some species dominated in isolated lagoons during high water and others in connected lagoons during the low water. These results were contrary to our expectations; we expected to observe highest species richness and abundance of rotifers in isolated lagoons during both extremes of the hydrological cycle. Our findings suggest the importance of connectivity among environments to rotifer species richness. The absence of an intense flood during 2001 facilitated development of rotifer populations during the high water period due to lack of dilution and high availability of food resources (phytoplankton).

The rearing of most marine fish species still relies on live food. Amino acids (AA) are the building blocks for protein synthesis, are important energy substrates, and are involved in specific physiological functions. Thus, the AA pools (free and protein-bound) of the rotifer Brachionus rotundiformis and of Artemia parthenogenetica metanauplii were analysed, after enrichment with different diets or at different salinities. The changes in these pools were related to their impact when used as feed for the developing fish larvae. Rotifers and Artemia were enriched for 24 h in microalgae, in commercial diets, or starved for the same time period. The enrichment at different salinities was also tested using Artemia. The free AA (FAA) quantity and quality was strongly affected by the enrichment used, in both rotifers and Artemia metanauplii. The relative FAA content was significantly higher in rotifers and Artemia enriched with microalgae than in the ones enriched with commercial products, and between the different microalgae tested, the enrichment in T. chui resulted in the highest FAA content for both preys. Differences regarding the FAA quantity and quality were also found between rotifers and Artemia. With the exception of the starved preys, a higher relative FAA content was found in rotifers than in Artemia metanauplii and while the FAA pool of the rotifers was dominated by alanine, taurine was the dominant AA in the FAA pool of Artemia. Salinity had only a small effect on the FAA pool of Artemia. Concerning the protein fraction, starvation increased the relative protein content in the rotifers. Among the metanauplii, the relative protein content was affected neither by the enrichment nor by salinity, except for a significantly lower content found when the microalgae Nannochloropsis gaditana was used. The quality of the protein pool is affected by the different enrichments, but not by salinity. However, the changes in the protein-bound AA pool were less pronounced than for the FAA pool and reflect differences in the protein content and/or quality of the diet. This study showed that the AA composition of cultured zooplankton is affected by feeding regime and by salinity. The choice of the best zooplankton enrichment and/or mixture of enrichments for the different fish larval stages, should take into account the AA composition, in order to fulfil the energetic and nutritional requirements of the larvae.

Little is known about the amino acid (AA) requirements of larval fish and their possible ontogenetic changes. This paper aims to contribute to the study of these requirements in two common cultured species in Southern Europe: gilthead seabream (Sparus aurata) and Senegalese sole (Solea senegalensis). Moreover, it is intended to identify possible dietary AA imbalances occurring in normal hatchery conditions for both species. Fish larvae were reared following standard procedures and the normal feeding schemes used in hatcheries, which includes the use of live prey for several weeks. The experiments were finished once the fish were adapted to a dry feed. Samples were collected at different points for dry weight, total protein, and AA analysis. The A/E ratios [each indispensable AA content x(total indispensable AA content including cysteine and tyrosine) super(-) super(1)x1000] of fish and food were compared to identify possible dietary AA imbalances. The AA profile of both fish species changed during ontogeny, but was more stable during seabream than Senegalese sole development. This is probably linked to the marked metamorphosis observed in sole. These changes in fish larval AA profile suggest that the AA requirements change during seabream and Senegalese sole ontogenesis. Several dietary AA deficiencies were found during the ontogenetic development of both species. These deficiencies result from ontogenetic changes in the fish AA profile, but also from differences in the AA composition of the different food items. These results suggest that both the live food (rotifers and Artemia at different developmental stages) and the dry feed used in the rearing of gilthead seabream and Senegalese sole does not have an AA profile that entirely meets the requirements for the early stages of these species.

Composition and seasonal dynamics of phytoplankton, bacteria, and zooplankton (including heterotrophic flagellates, ciliates, rotifers and crustaceans) were studied in 55 lakes in Northern Germany with different trophic status, ranging from mesotrophic to hypertrophic. Mean abundance and biomass of all groups increased significantly with trophic level of the lake, but bacteria and metazooplankton showed only a weak correlation and a slight increase with chlorophyll concentration. Composition of phytoplankton showed a dominance of cyanobacteria in hypertrophic lakes, whereas the importance of chrysophytes and dinophytes decreased with an increase in trophic status. Protozoans (heterotrophic flagellates and ciliates) made up 24% (mesotrophic lakes) to 42% (hypertrophic lakes) of total zooplankton biomass on average, and were dominated by ciliates (62-80% of protozoan biomass). Seasonally, protozoans can build up to 60% of zooplankton biomass in spring, when heterotrophic flagellates can contribute ~50% to protozoan biomass. Correlation analyses revealed significant relationships between the planktonic groups and indicated that pelagic food webs are influenced by both bottom-up as well as top-down mechanisms. Comparing lakes along a trophic gradient, resource parameters seem to be of major importance, whereas seasonal changes within a lake were perhaps regulated by the presence of predators.

Ecological effects of modern agrochemicals are typically limited to brief episodes of increased mortality or reduced growth that are qualitatively similar to natural disturbance regimes. The long-term ecological consequences of agrochemical exposures depend on the intensity and frequency of the exposures relative to the rates of recovery of the exposed populations. This paper explores the feasibility of using readily available life history information to quantify recovery rates of aquatic populations. A simple modeling framework based on the logistic population growth model is used to compare population recovery rates for different types of organisms and to evaluate the influence of life history, initial percent reduction, disturbance frequency, and immigration on the time required for populations to recover from simulated agrochemical exposures. Recovery models are developed for aquatic biota ranging in size and longevity from unicellular algae to fish and turtles. Population growth rates and recovery times derived from life history data are consistent with measured recovery times reported in mesocosm and enclosure experiments, thus supporting the use of the models for quantifying population recovery rates for ecological risk assessment.

Along the Atlantic coast black sea bass occur from the Gulf of Maine to Florida and support important commercial and recreational fisheries. Interest in commercial production of black sea bass has increased in recent years due to high demand and limited seasonable availability. Efforts towards large-scale production have been hampered by a high incidence of early larval mortality. Two of the most important environmental variables affecting hatchery production of marine finfish larvae are temperature and salinity. In the wild, larval black sea bass are found in waters with temperatures of 12-24 C and salinity levels of 30-35 ppt. Studies were conducted to define the temperature and salinity ranges that support growth and development of black sea bass during early life stages. Three developmental phases were investigated: 1) fertilization to hatch; 2) hatch through yolk sac absorption; and 3) during the initial exogenous feeding stage (5-14 days post hatch; DPH). Fertilized eggs were obtained by manual spawning of fish following administration of LHRH sub(a). Fertilized eggs were transferred to 300-mL glass Petri dishes or 500-mL beakers to assess the effects of salinity and temperature through hatch and yolk sac absorption, respectively. To determine environmental effects on growth and survival during initial exogenous feeding, 400 actively feeding larvae were cultured in green water and fed enriched rotifers for a 9-d period. For investigation of the effect of salinity, sea water (35 ppt) was diluted gradually to 15, 20, 25, and 30 ppt and maintained at 21 C. For examination of the effect of temperature, seawater was adjusted from 21 C to 12, 15, 21, 27, or 30 C at a rate of 3 C/h. No eggs hatched at 12 C or when salinity was maintained at 0 or 5 ppt. Hatching was uniformly high (=> 85%) at temperatures between 15 and 27 C and at salinities => 15 ppt. Survival through yolk sac absorption was greatest at temperatures between 18 and 27 C and at salinities => 20 ppt. Survival through first feeding stage was highest at temperatures => 18 C and 30 ppt salinity. Larval growth through first feeding was not significantly affected by salinity level but did increase with rearing temperature. The results indicate that survival and development of black sea bass during early life stages are most favorable at temperatures >18 C with salinity levels approaching full strength seawater.

Seasonal and daily patterns of zooplankton populations are often predictable in natural lakes. Distinct zonation and geomorphic differences in reservoirs, however, make ecological extrapolations from lakes to reservoirs uncertain. We describe the spatial and temporal distribution of zooplankton, algae, and water clarity across reservoir zones and along a depth gradient in Glen Elder Reservoir, Kansas. Daphnia species were most abundant in the lacustrine zone, with D. pulicaria numerically dominant in early spring and D. mendotae dominant later in 1999 and 2000. Rotifers (Keratella quadrata, Asplanchna spp.) were dominant in the riverine zone in 1999, 2000, and 2001. Algal biomass was not significantly different between zones through most of the sampling periods, except late April in 1999 and mid-April in 2000. Chlorophyll a exceeded 81 mug l(-1) in the lacustrine zone in mid- to late-April in 1999 and 2000, and exceeded 90 mug l(-1) in the riverine zone in mid- April. Water clarity was significantly lower in the riverine zone in 1999 and 2000. Most zooplankton taxa had similar depth distributions at night and day, indicating a lack of diel vertical migration behavior on a large scale. However, in small scale (30 cm vertical enclosures) laboratory experiments, both D. pulicaria and D. mendotae occupied significantly deeper depths (>25 cm) under lighted conditions in the presence of fish chemical cues compared to shallow water (7-17 cm) under dark conditions and in the absence of fish cues. These contrasting results suggest that, as in other studies, Daphnia sense cues from predators and alter their depth in the water column on small scales without natural constraints on movement and choices. However, other factors in the reservoir such as wind-generated water movements and cues from other predators may prevent depth choices similar to those seen under controlled conditions. These results illustrate biotic and abiotic differences between riverine and lacustrine zones in a large reservoir, and contrast with Daphnia depth segregation and migration patterns in natural lakes.

The chrysophyte genera Poterioochromonas and Ochromonas and their heterotrophic analogons, i.e. the 'Spumella-like' flagellates, account for a significant and often dominating fraction of the pelagic nanoplankton. Even though several osmotrophically and autotrophically grown strains of Ochromonas and Poterioochromonas are assumed to produce toxins, the potential toxicity has been investigated neither for its association with bacterivorous nutrition nor within the related exclusively heterotrophic 'Spumella-like' flagellates. We investigated the toxic potential of several flagellate strains using cultures of flagellates, cell extracts and filtrate of flagellate cultures. ne effect on potential predators was exemplarily tested for the cladoceran Daphnia magna and the rotifer Platyias sp. All tested heterotrophic and mixotrophic flagellate strains were toxic to zooplankton at abundances exceeding 10(4) flagellates mL(-1). For the rotfiers, survival on any of the flagellate strains was significantly lower than that in the control treatment (P < 0.001) already after 24 h. We conclude that (i) 'Spumella-like' flagellates can be toxic to Zooplankton, (ii) all tested flagellates, i.e. heterotrophic and mixotrophic flagellates feeding phagotrophically can be toxic to zooplankton and (iii) sublethal effects may be observed at typical field abundances, even though acute toxicity seems to be restricted to flagellate abundances observed only at peak events.

We determined the effect of dietary long-chain (> or = C20) PUFA (LC-PUFA), 20:5n-3 and 22:6n-3, on larval striped trumpeter (Latris lineata) biochemistry through early development and during live feeding with rotifers (Brachionus plicatilis). Rotifers were enriched using seven experimental emulsions formulated with increasing concentrations of n-3 LC-PUFA, mainly 20:5n-3 and 22:6n-3. Enriched rotifer n-3 LC-PUFA concentrations ranged from 10-30 mg/g dry matter. Enriched rotifers were fed to striped trumpeter larvae from 5 to 18 d post-hatch (dph) in a short-term experiment to minimize gross deficiency symptoms such as poor survival that could confound results. No relationships were observed between larval growth or survival with dietary n-3 LC-PUFA at 18 dph. The larval FA profiles generally reflected those of the rotifer diet, and significant positive regressions were observed between most dietary and larval FA at 10, 14, and 18 dph. The major exception observed was an inverse relationship between dietary and larval 22:5n-3. The presence of 22:5n-3 in elevated amounts when dietary 22:6n-3 was depressed suggests that elongation of 20:5n-3 may be occurring in an attempt to raise body concentrations of 22:6n-3. We hypothesize that accumulation of 22:5n-3 might be an early indicator of 22:6n-3 deficiency in larval fish that precedes a reduction in growth or survival. A possible role of 22:5n-3 as a biochemical surrogate for 22:6n-3 is discussed.

In response to drought bdelloid and monogonont rotifers undergo anhydrobiosis and are assumed to synthesize protective chemicals, which are commonly sugars. In contrast to most anhydrobionts, bdelloids have earlier been shown to lack trehalose as protective chemical, and more importantly to lack trehalose synthase (tps) genes. It remains to be assessed if the absence of trehalose is a characteristic common to the entire taxon Rotifera, or if it is limited to bdelloids, or is peculiar to the two bdelloid species investigated so far. In this study, anhydrobiotic adults of a bdelloid species (Macrotrachela quadricornifera) and resting eggs of a monogonont species (Brachionus plicatilis) were analysed by thin layer chromatography and gas chromatography to detect the presence of trehalose. No trehalose was detected in the bdelloid, while the anhydrobiotic resting egg of the monogonont rotifer contained about 0.35% trehalose of its dry weight. Although very little, the presence of trehalose in B. plicatilis suggests that the trehalose synthase genes, absent in bdelloid rotifers, are present in non-bdelloid rotifers.

Pigmentation, bio-optical characteristics and photophysiology, were studied in mesocosms with different N:P ratios. No significant difference in biomass or species composition was seen under different nitrogen to phosphorus ratios (N:P), but a temporal succession of different flagellate groups was observed in all mesocosms. An initial bloom of prymnesiophytes containing chlorophyll (Chl) c and 19' hexanoyloxyfucoxanthin (19' HOF) was followed by prasinophytes containing Chl b. Electron microscope analysis confirmed the presence of genera such as Chrysochromulina (Prymnesiophyceae), Tetraselmis and Pyramimonas (Prasinophyceae). Traces of prasinoxanthin in the pigment samples showed that smaller prasinophytes were also present. Chl b influenced the photophysiology of the prasinophytes resulting in higher Chl a-specific absorption, but a greater difference between absorption and scaled fluorescence excitation spectra indicated that light absorbed by Chl b is associated with photosystem I (PSI). Since a larger fraction of the light was absorbed by chlorophyll in PSI and/or photoprotective carotenoids, the light-saturated Chl a-specific rate of photosynthesis (P super(B) sub(m)) and maximum light utilization coefficient ( alpha super(B)) decreased when [Chl b] increased. The highest P super(B) sub(m) values were seen when the ratios of fucoxanthins to Chl a were high, indicating that prymnesiophytes might be more efficient in light harvesting and electron transport through photosystem II (PSII) by fucoxanthins and Chl c. Our results therefore indicate different light acclimation strategies in prasinophytes versus prymnesiophytes, which may be reflected in the successional appearance of these communities in the natural environment. We also suggest that grazing by ciliates and rotifers caused periodic decreases in phytoplankton biomass, which in turn gave rise to the phytoflagellate succession observed in the mesocosms.

The ciliate Euplotes vannus is a common protozoan in mass cultures of rotifers, and rapid reproduction of E. vannus occasionally reduces the rotifer yield. We performed a competition experiment between the rotifer Brachionus rotundiformis and the ciliate E. vannus. The ciliate was inoculated at three stages of the rotifer growth curve: the lag phase, the logarithmic growth phase and the stationary phase. When feeding on the alga Tetraselmis tetrathele, the ciliate increased and the rotifer growth was suppressed. The interference with rotifer growth was stronger in the lag and stationary phases than in the logarithmic growth phase. In contrast, when feeding on the alga Nannochloropsis oculata, the ciliate did not increase and the rotifer growth was similar to the control. In addition to the competition experiments, super(1) super(5)N incorporation experiments were performed on the ciliate to investigate its food preference. The nitrogen incorporation rates (% of body nitrogen h super(-) super(1)) of the ciliate were 0.7% through dead algae and 1.9% through rotifer feces when using T. tetrathele, and 0.4% through dead algae and 3.4% through rotifer feces when using N. oculata. The incorporation rate through bacteria-free rotifer feces was about one-third that of normal rotifer feces. These results indicated that the ciliate did not incorporate algal nitrogen directly, but rather through the microbial food chain, from phytoplankton to rotifer feces to bacteria. E. vannus incorporated the nitrogen of N. oculata and grew for a short time but the growth was soon suppressed. This growth inhibition may be due to allelopathy of N. oculata for E. vannus. Consequently, we propose that periodic addition of N. oculata should control E. vannus, and that this technique of applying allelopathy should be more sustainable than conventional treatments.

The relevance of predation as a factor mediating the competitive interaction among ecologically very similar species is investigated by experimentally analyzing the effect of the copepod predator Diacyclops bicuspidatus odessanus on three sibling rotifer species belonging to the Brachionus plicatilis species complex. These rotifer species are similar in shape but show notable differences in body size. Predator and prey species co-occur in brackish waterbodies close to the Mediterranean coast of Spain. First, we characterized differential vulnerability of rotifers to predation. A consistent tendency of higher predation rates on smaller prey (i.e., smaller species and younger individuals) was observed. Analysis of predation showed that predator contact rate did not differ significantly among prey species, but that attack, capture probabilities, and handling time did. Second, we performed population dynamics experiments with two prey species competing for a single resource at different levels of predation. Predation extended coexistence of the competing rotifers, whereas the inferior competitor was excluded in the absence of the predator. In some pairwise experiments, we found that the greater the predation level, the larger the relative increase in density of the inferior competitor. Our results suggest that predation can affect the dynamics of very similar competing species in natural aquatic communities, promoting coexistence.

Temporal and spatial heterogeneity of resources is likely to have dramatic effects on the behaviors of zooplankton and ichthyoplankton, which in turn are likely to have strong effects on ecological dynamics such as predation, growth, and mating. The objective of this study was to determine whether vertically thin layers of extreme prey concentration affect the vertical distribution of larval Pacific herring (Clupea pallasi). We employed 2-m tall experimental tanks equipped with video cameras that scanned the vertical extent of the tanks to investigate the effects of thin layers on the vertical distribution of 5- and 10-day-old herring larvae. Three treatments were established: (1) a thin layer of prey (rotifers, Brachionus plicatilis) through density (salinity) stratification, (2) homogeneous vertical distribution of both prey and density, and (3) density (salinity) stratification, but with a homogeneous distribution of prey. We found that in all treatments the majority of larval herring were at the surface, near the light, despite the absence of a peak in rotifer abundance at this depth in some instances. However, there were also clear effects of the thin layers; secondary subsurface peaks in herring abundance occurred at the mid- depths in the stratified tanks, in and around the thin layers. In addition, our results provide some evidence that thin layers specifically, rather than prey patches generally, influence the vertical distribution of larval herring, i.e. larvae may use the physical properties of thin layers to locate and distribute themselves, instead of reacting solely to the prey patches. Thus thin layers can affect directly the vertical distribution of larval herring, and perhaps indirectly their horizontal distribution, as herring larvae live in environments (e.g. estuaries) where advective transport is also often vertically heterogeneous.

Light exposure of aqueous suspensions of prednisolone and dexamethasone causes their partial phototransformation. The photoproducts, isolated by chromatographic techniques, have been identified by spectroscopic means. Prednisolone, dexamethasone and their photoproducts have been tested to evaluate their acute and chronic toxic effects on some freshwater chain organisms. The rotifer Brachionus calyciflorus and the crustaceans Thamnocephalus platyurus and Daphnia magna were chosen to perform acute toxicity tests, while the alga Pseudokircheneriella subcapitata (formerly known as Selenastrum capricornutum) and the crustacean Ceriodaphnia dubia to perform chronic tests. The photochemical derivatives are more toxic than the parent compounds. Generally low acute toxicity was found. Chronic exposure to this class of pharmaceuticals caused inhibition of growth population on the freshwater crustacean C. dubia while the alga P. subcapitata seems to be less affected by the presence of these drugs.

Sunlight exposure of aqueous suspensions of carboxin (1) causes its phototransformation to sulfoxide 2 and minor components. Similar effects are observed in the presence of humic acid or nitrate or at different pH values. Photoproducts 2-9 were isolated by chromatographic techniques and/or identified by spectroscopic means. Carboxin 1 and its main photoproduct sulfoxide 2 were tested to evaluate acute toxicity to primary consumers typical of the aquatic environment: the rotifer Brachionus calyciflorus and two crustaceans, Daphnia magna and Thamnocephalus platyurus. Chronic tests comprised a producer, the alga Pseudokirchneriella subcapitata, and a consumer, the crustacean Ceriodaphnia dubia.

Phylogeography structure of Brachionus calyflorious populations sampled from several lakes in Beijing and Jianghan lake region were studied on mitochondrial cytochrome oxidase subunit I gene (COI) partial sequences. 661 bp of the COI gene were amplified and sequenced. Sequences were moderately A + T rich (mean A + T content=65.6%), and the mean A + T contents were 56.8%, 58.3% and 81.4% in the first, second and third codon positions of the genetic codes, respectively. The A + T contents of DH-1 and DH-2 were lower than those of other haplotypes. 15 haplotypes were identified from 37 samples with 163 variation sites. According to the sample time, these haplotypes could be divided into two groups, March and October. Most substitutions of nucleotides occurred between the March group and October group. On the contrary, there were fewer substitutions among haplotypes within the same group. Calculated with Kumur 2-parameters model by software MEGA, pairwise sequences genetic distances among sequences ranged from 0.002 to 0.263. Pairwise sequences genetic distances among haplotypes sampled in same season ranged from 0.002 to 0.031; however, genetic distances among haplotypes sampled in different seasons were rather high, ranging from 0.248 to 0.263.

The potential of Toxkit microbiotests to detect and analyze pollution in agricultural soil and the quality of compost was studied. The toxicity tests used included seed germination biotests using cress salad (Lepidum sativum L.), tomato (Lycopersicum esculentum L.), and cucumber (Cucumis sativus L.), and the Toxkit microbiotests included those with microalgae (Selenastrum capricornutum), protozoa (Tetrahymena thermophila), crustaceans (Daphnia magna, Thamnocephalus platyurus, and Heterocypris incongruens), and rotifers (Brachionus calyciflorus). Experiments on compost were undertaken in a modified solid-state fermentation system (SSF) and under field conditions (in a windrow). To promote the composting process, two strains of Trichoderma (Trichoderma lignorum and Trichoderma viride), as well as a nitrification association that regulated the nitrogen-ammonification and nitrification processes were applied. (Copyright 2004 Wiley Periodicals, Inc.)

The aim of the study was to test the hypothesis that the size distribution of sand grains in lake beach should affect the species composition, densities and body-size structure of psammon communities of Rotifera. Studies were carried out in hydro-, hygro- and euarenal zones of 38 beaches (5 to 50 m long and 1 to 10 m wide) in 16 lakes of different trophic status and morphometry (Masurian Lakeland, Poland). Porosity has no impact on psammon rotifer numbers as well as body-size of animals does not seem to play a significant role in species preference to different size classes of sand grains. However, the significant correlations were found between the rotifer numbers and the share of grain size fraction 0.25-1.00 mm (positive) and the share of the largest (i.e. > 1 mm) fraction (negative). The psammobionts generally are more related to the grain size fraction 0.5-1.0 mm than the psammoxenes and psammophiles. Although particular rotifer species prefer different grain size fractions, bdelloids are the only group of Rotifera preferring the smallest (<0.125 mm) grain fraction.

According to a theory of lake restoration through food web manipulation, the removal of planktivorous fish results in the development of large cladocerans (mostly daphnids) and, consequently, in reduction of algal biomass. However, as a rule, publications devoted to different aspects of the theory completely neglected other groups of plankton invertebrates, thought they may reach very high densities. Investigations carried out in five Masurian lakes differing in trophic state and mixis showed that in most lakes the role of small cladocerans, copepods, rotifers and protozoans in the consumption of algal food and nutrient regeneration was more important than the role of large daphnids. Daphnia cucullata played more significant role (excreting 28% of the regenerated P) during "clear water phase" only in one lake - Lake Glgbokie. In the remaining lakes more important was an impact of Bosmina longirostris (11-59% of the regenerated P), younger stages of cyclopoids (23%), ciliate Strobilidium humile (20%) or detritophagous rotifer Keratella cochlearis (21%). Evidenced in many papers special role of large cladocerans in clearing lake water is explained by their combined direct (by "efficient" filtering) and indirect (suppression of ciliates and rotifers through predation, interference and resource competition) impact on nutrient sedimentation or exclusion from internal cycling.

Chlorella species, unicellular common green algae, are wildly distributed in different waters (fresh water and sea), soil and air. Because of easy cultivation and (or) enriched bioactive products, some are used as models for the study of plant metabolism and function. Researchers on Chlorella face many problems caused by unclear traditional classification of Chlorella. As morphological characteristics are few, it is difficult to classify Chlorella cells correctly using traditional taxonomic methods. Chemotaxonomy is therefore an importance alternative in algae classification. Chemotaxonomy classification is based on internal differences in chemistry including pigments, fatty acids, lipids, protein and nucleic acids. One marine strain, identified as Chlorella sp. 1061, is widely used in China as feed for rotifers and brine shrimp. Unlike bright green color in other Chlorella strains, Chlorella. sp. 1061 is dull yellow-green indicating that Chlorella sp. 1061 may have distinct pigments. Differences are also seen in fatty acids. Chlorella sp. 1061 contains higher amounts of EPA than other Chlorella strains do. Therefore, the taxonomic position of Chlorella sp. 1061 is questionable. On the other hand, although Chlorella sp. 1061 is widely cultivated in China with high potential commercial value of high amount of EPA, few physiological and biochemical data is available. Considering collectively the pigment, polar glycerolipids, fatty acid and membrane lipid of Chlorella sp. 1061, the taxonomic position of Chlorella sp. 1061 should be reconsidered. Pigment composition of Chlorella sp. 1061 was analyzed by HPLC, 6 special peaks were identified according to retain time of standards indicating 6 pigments. TLC and GC were applied to characterize membrane lipids and fatty acids of this alga.

Olive oil mill wastewaters (OMW) are recalcitrant to biodegradation for their toxicity due to high values of chemical oxygen demand (COD), biological oxygen demand (BOD), and phenolic compounds. In the present study OMW, collected in southern Italy, were subjected first to a chemical oxidative procedure with FeCl3 and then to a biological treatment. The latter was performed in a pilot plant where mixed commercial selected bacteria, suitable for polyphenols and lipid degradation, were inoculated. The effect of treatments was assessed through COD removal, reduction of total phenols, and decrease of toxicity using primary consumers of the aquatic food chain (the rotifer Brachionus calyciflorus and the crustacean Daphnia magna). The results showed that the chemical oxidation was efficacious in reducing all parameters analyzed. A further decrease was found by combining chemical and biological treatments.

Rotifers have articulated hard jaws called "trophi", whose shapes are considered species-specific for monogonont rotifers but not for bdelloid rotifers. We present a geometric morphometric analysis of size and shape of bdelloid jaws, carried out on SEM pictures of trophi of nine morphospecies belonging to the genus Rotaria, using six landmarks. The Study Shows that trophi call also have species-specific form in bdelloids and suggests future directions for the analysis of the relationship between shape, size and diet in modelling trophi morphology during the evolution of Rotaria.

We describe some rare epizoic rotifers found on Potamon fluviatile from Italy. Three species are discussed: Lecane branchicola (Monogononta, Lecanidae; new synonym: L. piovanellii), Anomopus telphusae Piovanelli, 1903 and Embata parasitica (Bdelloidea: Philodinidae). Lecane branchicola, previously considered a nomen nudum after Bartos (1957), is redescribed, and its identity is stabilized by the designation of a neotype. Both L. branchicola and A. telphusae are particularly rare, and have been found on a few occasions only. Lecane branchicola appears to be restricted to a specific body part of their host, namely the branchial chamber. On the contrary, E. parasitica has been recorded as epizoic from several hosts and regions. SEM photographs of the trophi of the three species are presented.

Although species diversity is often correlated with ecosystem size in a consistent manner, mechanistic explanations of when and why diversity is related to size remain elusive. Rarely considered in understanding size-diversity relationships is the history of community assembly. I conducted a laboratory microcosm experiment with freshwater protists and rotifers to test for interactive effects of assembly history and ecosystem size on species diversity. The experiment used a two-way factorial design with four assembly sequences and four ecosystem sizes as treatments. Community dynamics were monitored for about 50-100 generations. The results show that history affected diversity more strongly in smaller ecosystems, presumably owing to greater priority effects. Consequently, history determined when diversity was significantly related to ecosystem size. The results also suggest that long-term transient community dynamics can make assembly history important for community structuring even in the absence of alternative stable states. Because species immigration is essentially stochastic, ecosystem size is variable, and priority effects can be strong in many natural systems, the history X size interaction revealed in this study also has the potential to shape natural size-diversity patterns.

Methyl parathion is a commonly used insecticide in Mexico to eradicate insect pests. We evaluated the effects of this insecticide on rotifer B. angularis using both acute and chronic toxicity tests. Median lethal concentration (LC50) of methyl parathion for B. angularis for a 24-h bioassay in the presence and absence of an algal diet was derived. Elevated LC50 due to the survival of a greater number of test individuals in the presence of food was observed. Regardless of the toxicant concentration, population growth curves of the animals maintained at the low food level (0.75t10 super(6) cells ml super(-1)) had a longer lag phase than those at the high food level (1.5t10 super(6) cells ml super(-1)). Regardless of food level, an increase in the toxicant concentration in the medium resulted in decreased population growth. The lowest peak population density (50 ind. ml super(-1)) was observed at the highest toxicant concentration and the lower food level. The highest population density (200 ind. ml super(-1)) was observed in the controls at high food level. The rates of population increase per day (r) in the controls were higher (from 0.14 to 0.37 depending on the food level). Irrespective of food level, there was a decrease in the r values with increasing pesticide concentration in the medium. In order to detect the effect of population density on the growth rates in relation to the toxicant stress, we plotted the daily growth rate against initial density for the entire duration of the experiment. We observed the existence of a significantly inverse relation at all treatments except at the low food level and high toxicant concentrations (0.625 and 1.25 mg l super(-1)). We discuss the role of algae in the toxicity of methyl parathion to zooplankton.

In the heterogonic life cycle of monogonont rotifers, amictic (female-producing) females develop from two types of eggs: fertilised resting (diapausing) eggs and parthenogenetic subitaneous eggs. Females hatched from resting eggs initiate clonal populations by female parthenogenesis and are called stem females. This study compares females from resting and parthenogenetic eggs that were produced under identical culture conditions and were of similar birth order. Newborn stem females had many more lipid droplets in their tissues than similar-sized, newborn females from parthenogenetic eggs. When neonates were stained with Nile Red and viewed under epifluorescent illumination, these droplets were shown to be sites of neutral-lipid storage products. Stem females had no posterolateral spines and short anterior spines, while their mothers and offspring in subsequent, parthenogenetic generations typically had long posterolateral spines and elongated anterior spines. Newborn stem females survived starvation significantly longer than newborn females from parthenogenetic eggs. When females from resting and parthenogenetic eggs were cultured from birth to death at a high food concentration, the reproductive potential (r day super(-1)) of the stem females was significantly higher (0.82-0.88 versus 0.70), primarily because of egg production at an earlier age. The mean lifetime fecundity (R sub(o)) of stem females was significantly greater than that of females from parthenogenetic eggs. Extensive lipid reserves should increase the ability of stem females to colonise new habitats. Firstly, compared with females from parthenogenetic eggs, stem females are more likely to experience starvation or food limitation. Resting eggs hatch in response to physical and chemical factors that are not directly related to food availability, and from sediments that may be far from food-rich surface waters. Secondly, when food is abundant, stem females have a greater reproductive potential

Sexual reproduction in cyclically parthenogenetic rotifers results in the production of diapausing, fertilized (resting) eggs, which can survive for decades in sediment egg banks. Stem females hatching from these eggs can differ from genetically identical ones produced in subsequent parthenogenetic generations. Differences involve the inhibition of sexual reproduction, which may persist for many parthenogenetic generations; reduced morphology (apterous Polyarthra, shorter-spined Brachionus); and larger stores of lipid. These features of stem females may facilitate colonization by favoring population growth via female parthenogenesis and by decreasing food requirements for survival and reproduction. Fertilized eggs in dried sediments probably hatch soon after being flooded by rising water levels. Eggs in permanently submerged sediments may be in environments that inhibit hatching (e.g., darkness, low water temperature, low dissolved oxygen) and hatch only when brought to the sediment surface or resuspended into the water column by currents or bioturbation. Laboratory experiments show that the hatching of diapausing, fertilized eggs can require light and temperatures suitable for population development or specific changes in temperature consistent with a new growing season. The limited data that exist on their emergence from fertilized eggs in natural systems come from sediment traps, from the occurrence in the water column of apterous Polyarthra or empty egg shells, and from calculations of negative mortality rates of planktonic populations. Fertilized eggs often hatch at the beginning of the growth season but may continue to hatch intermittently thereafter. The extremely high genotypic diversity of some natural rotifer populations indicates extensive hatching of stem females from the sediment egg bank.

Limnological characteristics of Lake Burdur in Lake District in south-western Turkey are presented. It is a deep, tectonic (estimated max. depth 100 m), athalassic, highly alkaline, and saline lake. A set of physical and chemical variables was monitored, phyto- and zooplankton was sampled from surface layer of the lake during 1997. Physico-chemical variables indicated that the lake is hyposaline and composed of some hydrochemically different water layers formed by groundwater sources located on the bottom of the lake. The phytoplankton composition of Lake Burdur consisted of Cyanophyta, Chlorophyta, Bacillariophyta, Dinophyta, and Chrysophyta. The abundance and number of species of Chlorophyta and Cyanophyta were higher than the other taxa. The zooplankton composition of the Lake consisted of Rhizopoda, Rotifera, and Crustacea. Number of species of Rotifera was higher than the other taxa. The diversities of the phyto- and zooplankton were calculated according to the Shannon-Weaver diversity index. The diversity of each group was found to be low in the lake.

Micrognathozoa is the most recently discovered higher metazoan lineage. The sole known species of the group, Limnognathia maerski, was originally reported from running freshwater in Disko Island (Greenland), and has recently been recorded from the subantarctic region. Because of the presence of a particular type of jaws formed of special cuticularized rods, similar to those of gnathostomulids and rotifers, the three metazoan lineages were considered closely related, and assigned to the clade Gnathifera. A phylogenetic comparison Of four molecular loci for Limnognathia maerski and other newly generated sequences of mainly acoelomate animals showed that Micrognathozoa may constitute an independent lineage from those of Gnathostomulida and Rotifera. However, the exact position of Micrognathozoa could not be determined due to the lack of support for any given relationships and due to the lack of stability in the position of Limnognathia maerski under analysis of different loci and of different parameter sets for sequence comparison. Nuclear loci tend to place Micrognathozoa with the syndermatan/cycliophoran taxa, but the addition of the mitochodrial gene cytochrome c oxidase subunit I favors a relationship of Micrognathozoa to Entoprocta. (C) The Willi Hennig Society 2004.

The aim of this paper is to study long-term changes in the zooplankton of a subalpine locality unaffected by direct anthropogenic disturbances. The material has been collected during the period 1985-1997; since 1988 a standardised sampling program has been followed, with five sampling dates during the ice free period (June-October) at three fixed stations. Altogether 17 species of Rotatoria, 9 species of Copepoda and 11 species of Cladocera were recorded. Of these 10 species of Rotatoria, two species of Copepoda and five species of Cladocera occur regularly in the plankton. Polyarthra vulgaris dominate among the rotifers together with Kellicottia longispina and Conochilus unicornis. The crustacean community is dominated by the copepod Cyclops scutifer, and the cladocerans Bosmina longispina, Holopedium gibberum and Daphnia longispina. The cladocerans Bythotrephes longimanus, Polyphemus pediculus, and the copepods Arctodiaptomus laticeps and Heterocope saliens all occur regularly, but at low densities. The zooplankton density is low in May/June and peaks in August and September, but the timing of maximum densities varies from year to year. By numbers, the rotifers strongly dominate with densities 10-15 times higher than the crustaceans. The annual maximum density (rotifers plus crustaceans) ranged from 50 ind. l super(-1) (1985, 1988) to 450 ind. l super(-1) (1995). Mean density is about 140-150 ind. l super(-1). By biomass (dry weight), the cladocerans constitute 60%, while the copepods and rotifers constitute 30% and 10% of the zooplankton, respectively. The annual maximum has varied between 70 and 260 mu g dw l super(-1), with 170 mu g dw l super(-1) as the mean level. C. scutifer usually has a one-year lifecycle without diapause, but a small fraction of the population has a two-year lifecycle. The life cycle in 1989 and 1990 differed strongly from the other years. The life cycles of B. longispina, D. longispina and possibly also H. gibberum and A. laticeps, indicate two generations during the summer. H. gibberum and H. saliens pass the winter as resting eggs. The other crustacean species, except C. scutifer, pass the winter mainly as resting eggs, but all have a small winter population in the water mass. C. scutifer is the only species without resting eggs. The vertical distribution normally shows highest density between 5 and 10 m depth. However, during some periods maximum density is observed close to the surface, while at other times it is seen deep in the hypolimnion. The vertical distribution is most pronounced when the thermocline is sharp, and less pronounced during the full circulation in autumn. The vertical migration may also be pronounced, especially in B. longispina, with high density near the surface during the night. The vertical migration is less pronounced among the rotifers and copepods. The degree of vertical migration varies with temperature and food conditions. There is little variation from year to year in species composition, but large variation in species dominance, seasonal development, population density, and vertical and horizontal distribution during the sampling period. Variations in temperature, food condition, predation, and water through-flow are possible causes for the observed differences between the years. Input of allochthonous material is especially important. However, no clear correlation have been found between the development of the plankton community and these environmental factors. Hence, these interactions are complex and multifactorial.

Populations of soil nematodes were studied in vital Norway spruce forests, standing dead spruce forests destroyed by bark beetles, and in clearings left after logging dead trees. Investigations were carried out in the Sumava Mountains (Bohemian Forest; Czech Republic) in localities over 1000 m a.s.l. The total mean abundance of nematodes in vital spruce forests was 1817 X 10(3) -4877 x 10(3) individual s/m(2), in dead forests 1536 x 10(3) -2339 x 10(3) individual s/m(2), and in clearings 1342 x 10(3)-3864 x 10(3) individuaIs/m(2). The total mean biomass was 442-777, 493-730, and 382-582 mg m(-2), respectively. Vital spruce forests were characterized by a predominance of Filenchus, the abundance of which was lower in dead spruce forests and after tree logging. Clearings were characterized by a predominance of Aglenchus, the abundance of which increased with the age of clearing and increased proportion of grass in understorey plant cover. The structure of nematode communities changed in a gradient from vital forests through dead forests to clearings. Maturity indices did not differ among diverse stands. The Matrix classification of nematode functional guilds suggested that the soil environment in most localities studied had a stressed and degraded food web, depleted with a high C:N ratio, and fungal decomposition channels. (C) 2004 Elsevier B.V. All rights reserved.

The purpose of this study was to select, identify and characterise bacteria as a disease control measure in the rearing of marine fish larvae (turbot, Scophthalmus maximus). Thirty-four out of 400 marine bacterial strains exhibited in vitro anti-bacterial activity against three fish larval pathogens. Two strains originated from culture collections and thirty two strains were isolated directly from turbot larvae rearing units using a pre-selection procedure to facilitate detection of antagonists. Approximately 8,500 colonies from colony-count plates were replica-plated on agar seeded with Vibrio anguillarum, and 196 of them caused zones of clearing in the V. anguillarum agar layer. Of these, 32 strains exhibited reproducible antibacterial properties in vitro when tested against the fish pathogens V anguillarum 90-11-287,V splendidus DMC-1 and a Pseudoalteromonas HQ. Seventeen antagonists were identified as Vibrio spp. and four of twelve tested were lethal to yolk-sac larvae. The 15 remaining strains were identified as Roseobacter spp. based on phenotypic criteria and 16S rDNA gene sequence analysis of two strains representing the two major RAPD groups. Most of the remaining 164 strains selected in the initial replica plating were identified as Vibrionaceae or Pseudoalteromonas. Roseobacter spp. were not lethal to egg yolk sac turbot larvae and in two of three trials, the mortality of larvae decreased (p > 0.001) in treatments where 10(7) cfu/ml Roseobacter sp. strain 27-4 was added, indicating a probiotic potential.

By population accumulative culture, Chlorella pyrenoidosa (at 6.0 x 10 super(6) cells/mL) as the rotifer's food, the effects of temperature on the population growth, body size, and egg size of three different strains of B. angularis, respectively from Qingdao, Guangzhou and Wuhu cities, were studies at 20 degree C, 25 degree C and 30 degree C. The results showed that temperature affected the population growth rate, body size, and egg size significantly. The optimum temperature of population growth QD strain was 30 degree C, and that of GZ strain was 25 degree C; WH strain had 100% mortality at 30 degree C. The relationships between temperature and population growth rate of both QD and GZ strain were curvilinear.

BACKGROUND: The photolysis of pesticides is of high current interest since light is one of the most important abiotic factors which are responsible for the environmental fate of these substances and may induce their conversion into noxious products. The action of light can also be mediated by oxygen and synthetic or naturally occurring substances which act as sensitizers. Our objective in this study was to investigate the photochemical behaviour of the systemic fungicide furalaxyl in the presence of oxygen and various sensitizers, and to compare the toxicity of the main photoproduct(s) to that of the parent compound. Previous reports on the direct photolysis of the pesticide demonstrated a very slow degradation and the only identified photoproducts were N-2,6-xylyl-D,L-alaninare and 2,6-dimethylaniline. METHODS: Solutions of furalaxyl in CH3CN were photooxygenate using a 500W high-pressure mercury lamp (through a Pyrex glass filter, lambda>300 nm) or a 650W halogen lamp or sunlight and the proper sensitizer. When sunlight was used, aqueous solutions were employed. The photodegradation was checked by NMR and/or GC-MS. The photoproducts were spectroscopically evidenced and, when possible, isolated chromatographically. Acute toxicity tests were performed on the rotifer Brachionus calyciflorus, the crustacean cladoceran Daphnia magna and the anostracan Thamnocephalus platyurus, while chronic toxicity tests (sublethal endpoints) comprised a producer, the alga Pseudokirchneriella subcapitata and the crustacean Ceriodaphnia dubia, as a consumer. RESULTS AND DISCUSSION: In the presence of both oxygen and sensitizer, furalaxyl underwent rapid photochemical transformations mainly to N-disubstituted formamide, maleic anhydride and a 2(5H)-furanone derivative. The formation of these products was rationalized in terms of a furan endoperoxide intermediate derived from the reaction of furalaxyl with active dioxygenated species (singlet oxygen, superoxide anion or ground state oxygen). The 2(5H)-furanone exhibited a higher toxicity than the parent compound. CONCLUSION: This work reports the first data on the photosensitized oxygenation of furalaxyl with evidence of the high tendency of the pesticide to undergo photodegradation under these conditions leading, among other things, to a 2(5H)-furanone, which is more toxic than the starting furalaxyl towards aquatic organisms. RECOMMENDATIONS AND OUTLOOK: Investigation highlights that the photolytic fate of a pesticide, although quite stable to direct photoreaction due to its low absorption of solar radiation at ground level, can be significantly influenced in the environment by the presence of substances with energy or electron-transfer properties as natural dyes, e.g. chlorophyll, or synthetic pollutants, e.g. polycyclic aromatic hydrocarbons (PAH).

The application of a battery of toxicity and genotoxicity tests on pore water in parallel and in combination with physico-chemical analyses and benthic macroinvertebrate community investigations is discussed as a tool to assess the environmental quality of the Volturno River in South Italy. Toxicity testing was performed on the rotifer Brachionus calyciflorus and the crustacean Daphnia magna. Genotoxicity was determined by the SOS chromotest and Mutatox system. The biotic index used for macroinvertebrates was the extended biotic index that was developed to verify if the observed benthic community accords with the expected one for an identical environment without anthropic contaminations. The physico-chemical characterization of the surface waters showed a declining trend from up-river to down-river for dissolved oxygen and conductivity. Also, chemical variables showed a worsening along the river axis showing an increase in ammonium, phosphates, sulfates, and heavy metals. The assessment of macro-invertebrates reflected the general ecological deterioration occurring to chemical as well as toxic and genotoxic pollution. Furthermore, benthic community composition and the sediment contamination of toxic and genotoxic substances were shown to be correlated. We concluded that investigations on pore water, integrated with benthic macroinvertebrate communities, could provide the basis for a robust monitoring of rivers.

Olive-oil-mill wastewater (OMW) has significant polluting properties due to its high levels of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and phenols. In the present study, different commercial bacterial formulations were used in the biological treatment of OMW. COD and toxicity testing using primary consumers of the aquatic food chain (the rotifer Brachionus calyciflorus and the crustacean Daphnia magna) were employed to evaluate abatement of the organic load and reduction of the toxic potential. In addition, the four most active formulations were tested mixed pair-wise on the basis of their unique characteristics in order to evaluate the improvement of treatment. The effect of treatment was assessed by measuring COD removal, reduction of total phenols, and decreased toxicity. The results obtained with the mixed formulations showed that the maximum removal of the organic load was about 85%, whereas phenols were reduced by about 67%. The toxicity for rotifers decreased by 43% and for crustaceans by about 83%.

1. Herbivorous zooplankton face considerable temporal and spatial variation in food quality, to which they respond by adapting their life histories. Zooplankton may even take up mineral nutrients directly, and use these to counter the effects of algal nutrient limitation (mineral compensation). This study examined the life history of the rotifer Brachionus calyciflorus fed phosphorus-, and nitrogen-limited Scenedesmus obliquus (Chlorophyta), and investigated whether B. calyciflorus was capable of mineral compensation. 2. Both phosphorus- and nitrogen-limited algae gave similar life history responses: somatic growth and reproduction were reduced, whereas lifespan remained unaffected. 3. No evidence was found for mineral compensation in B. calyciflorus in relation to detrimental life history effects, so mineral compensation does not seem to be relevant for this species under field conditions. 4. The similarity in life history responses of B. calyciflorus and the low levels of omega -3 PUFAs in both phosphorus- and nitrogen-depleted algae suggest that omega -3 PUFAs were limiting to B. calyciflorus, although other (bio)chemicals or mineral nutrients may also have been important. 5. No trade-off was observed between life span and reproduction during algal nutrient limitation. Reduced population growth rates of B. calyciflorus were caused by shorter reproductive periods.

A method was developed to allow direct measurements of predation exerted by metazooplankton on ciliates. The method relied on the use of ciliates labelled with fluorescent microparticles (FMP). Optimal labelling conditions were determined with ciliates from cultures (Tetrahymena pyriformis) and with natural ciliate assemblages sampled in a river. Labelled T. pyriformis were used as tracer food to determine gut passage time (GPT) and ingestion rates of the rotifer Brachionus calyciflorus in the laboratory. Predation of metazooplankton from the lowland river Meuse (Belgium) was determined by labelling natural assemblages of ciliates and using them as tracer food for metazooplankters sampled in the river. Optimal labels of ciliates, i.e. sharp distribution of FMP in cells, were obtained with short incubations (10 min) and low FMP concentrations (1 x 10(5) mL(-1)). GPT varied between 30 and 45 min for B. calyciflorus and from 25 up to >35 min for rotifers from the river. The ingestion rate of B. calyciflorus fed with T. pyriformis was 3.3 +/- 0.6 ciliate rot(-1) h(-1), i.e. 1.4 +/- 0.3 ngC rot(-1) h(-1). Metazooplankton species for which the ingestion of ciliates could be measured were the rotifers Keratella cochlearis, Euchlanis dilatata and Synchaeta spp. Ingestion rates measured ranged from 0.4 to 12.5 ngC rot(-1) h(-1). The method proposed proved to be useful in estimating the predation of microplankton on ciliates in semi- in situ conditions; in further developments, labelled natural assemblages of ciliates could be used for in situ incubations with the Haney chamber.

Fast ice and underlying water of the northern Baltic Sea were sampled at 1 wk intervals during winter 2000 in a coastal location in SW Finland. To investigate seasonal succession and interactions inside the food web and between the food web and physical and chemical properties of the ice, several biological (chlorophyll a, abundance of bacteria, flagellates and ciliates, bacterial cell volume and leucine incorporation, POC), chemical (total and dissolved nutrients) and physical (salinity, temperature) parameters were measured. The first ice-algae bloom with chlorophyll a (chl a) concentrations of up to 18.5 mu g/L occurred in mid-January, followed by the main ice-algae bloom in March and a heterotrophic postbloom situation shortly before the ice deteriorated in April. The ice-organism assemblage was autotrophy-dominated; during the entire ice-covered period, ice algae formed on average 82 plus or minus 10% (mean plus or minus SD) of the organism biomass. The largest heterotrophic groups by biomass were bacteria (16.7 plus or minus 9.4%), ciliates and metazoans (4.4 plus or minus 2.7 and 4.4 plus or minus 4.8%, respectively). The ice food-web was characterized by the importance of ice bacteria and the presence of a potential microbial loop (bacterial secondary production accounting for a mean of 27.1 plus or minus 19.3 mu mol C/m super(2)/d), grazing control on bacteria and flagellates, and also possible 'shortcuts' such as ciliate grazing on bacteria and metazoan herbivory. An ice-sheet warming event in February clearly affected the physical and chemical properties of the ice as well as the structure and function of ice-organism assemblages. Ice organisms probably controlled dissolved nutrient concentrations inside the ice by uptake and regeneration.

Vertical differences in food web structure were examined in an extremely acidic, iron-rich mining lake in Germany (Lake 111; pH 2.6, total Fe 150 mg L super(-1)) during the period of stratification. We tested whether or not the seasonal variation of the plankton composition is less pronounced than the differences observed over depth. The lake was strongly stratified in summer, and concentrations of dissolved organic carbon and inorganic carbon were consistently low in the epilimnion but high in the hypolimnion. Oxygen concentrations declined in the hypolimnion but were always above 2 mg L super(-1). Light attenuation did not change over depth and time and was governed by dissolved ferric iron. The plankton consisted mainly of single-celled and filamentous bacteria, the two mixotrophic flagellates Chlamydomonas sp. and Ochromonas sp., the two rotifer species Elosa worallii and Cephalodella hoodi, and Heliozoa as top predators. We observed very few ciliates and rhizopods, and no heterotrophic flagellates, crustaceans or fish. Ochromonas sp., bacterial filaments, Elosa and Heliozoa dominated in the epilimnion whereas Chlamydomonas sp., single-celled bacteria and Cephalodella dominated in the hypolimnion. Single-celled bacteria were controlled by Ochromonas sp. whereas the lack of large consumers favoured a high proportion of bacterial filaments. The primarily phototrophic Chlamydomas sp. was limited by light and CO sub(2) and may have been reduced due to grazing by Ochromonas sp. in the epilimnion. The distribution of the primarily phagotrophic Ochromonas sp. and of the animals seemed to be controlled by prey availability. Differences in the plankton composition were much higher between the epilimnion and hypolimnion than within a particular stratum over time. The food web in Lake 111 was extremely species-poor enabling no functional redundancy. This was attributed to the direct exclusion of species by the harsh environmental conditions and presumably enforced by competitive exclusion. The latter was promoted by the low diversity at the first trophic level which, in turn, was attributed to relatively stable growth conditions and the independence of resource availability (inorganic carbon and light) from algal density. Ecological theory suggests that low functional redundancy promotes low stability in ecosystem processes which was not supported by our data.

The uptake of organic substrates by heterotrophic planktonic organisms was studied along the freshwater Elbe Estuary in May, July and October 2000 using C-13 analysis of individually isolated dominant species of copepoda, cladocera, rotifera and ciliata. Non-sedimenting suspended particulate matter (SPMns) was separated from sedimenting matter and further analysed for the chemical composition of its different size fractions in order to estimate substrate availability. Particles <5 mum accounted for similar to15% of total SPMns [similar to40 mg dry weight (DW) L-1] and contained C:N ratios indicating a predominance of living matter (i.e. mass C:N of phytoplankton). All species under study exhibited a high capacity for selective feeding with little variation in the diet along the whole freshwater profile. Picoplankton of 0.2-1.2 mum formed mainly by bacteria had a delta(13)C value of -26parts per thousand in May and July and -29parts per thousand in October, similar to the delta(13)C of the dissolved organic carbon (DOC). Bacteria did not fractionate isotopically and did not preferentially consume specific subunits of their substrate, i.e. they exhibited no trophic shift. It appears that phytoplankton exudates were a minor component to total DOC in this estuary. Phytoplankton was the exclusive food for all phagotrophic organisms under study in July, thus only one trophic level was exhibited. During May and October the grazers under study used different substrates, resulting in a planktonic food web of three trophic levels formed by different species of the taxonomic groups under study. The results indicate a conditioned behaviour with regard to substrate selection allowing the grazers to produce high abundances even when particles were abundant and competition for phytoplankton was high.

Species diversity at the local-community scale can be altered by numerous factors, including disturbances, predators, and resource levels. Intermediate levels of these three factors are predicted to enhance coexistence and diversity. However, no study has examined how these factors may interact to alter community composition. The protozoan and rotifer community that colonized containers set in a forest was used to examine the interactions between these local community processes. We conducted a fully factorial microcosm experiment that manipulated disturbance frequency, predator density, and resource levels to examine protozoan and rotifer richness, community composition, and species abundance. Species richness was significantly altered by disturbances and predators, while predator densities interacted with disturbances and resources. Total abundance was significantly affected by each treatment, as well as a disturbance and predator interaction. We found that community composition was altered by each of the treatments and their interactions, indicating that different groups of species were present depending on the treatments. These results indicate that strong species sorting occurs in this community. Understanding these factors alone and in concert can provide insight to the potential complexities that underlie community structure and species composition.

The pattern of muscles in the actively swimming predatory rotifer Asplanchnopus multiceps is revealed by staining with tetramethyl-rhodamine isothiocyanate (TRITC)-labelled phalloidin and confocal scanning laser microscopy (CSLM). The major components of the musculature are: prominent semicircular muscles of the corona; paired lateral, dorsal and ventral retractors in the trunk; a network of six seemingly complete circular muscles and anastomosing longitudinal muscles in the trunk; two short foot retractors, originating from a transverse muscle in the lower third of the trunk. The sphincter of the corona marks the boundary between the head and the trunk. The muscular patterns in rotifers with different lifestyles differ clearly, therefore, the muscular patterns seem to be determined by the mode of locomotion and feeding behaviour.

Phytoplankton, mesozooplankton, mysids and fish larvae were studied during 15-29 annual cycles measured weekly to monthly in Paernu Bay, the Gulf of Riga. The monthly variability of the biological data was related to temperature, ice conditions, salinity, influx of nutrients, the North Atlantic Oscillation (NAO) index, cloudiness and solar activity. Phytoplankton development was mainly a function of the NAO index. For the whole study period the abundance of zooplankton increased with increasing water temperature and solar activity. Significant correlations between phytoplankton and zooplankton densities were found until 1990. After the invasion of the predatory cladoceran Cercopagis pengoi in 1991, the zooplankton community was likely to be regulated by the introduced species rather than phytoplankton dynamics. The increased abundances of rotifers and copepods triggered the increase in mysid densities. The development of herring larvae was positively affected by the high density of copepods and rotifers but also by increased eutrophication. Until 1990 there was no significant relationship between the density of zooplankton and herring larvae. A negative relationship between the density of zooplankton and herring larvae in the 1990s suggests that the major shift in zooplankton community resulted in food limitation for herring larvae. The results indicated that (1) atmospheric processes in the northern Atlantic explain a large part of the interannual variation of the local phytoplankton stock, (2) trophic interactions control the development of pelagic communities at higher trophic levels, and (3) the introduction of an effective intermediate predator has repercussions for the whole pelagic food web in Paernu Bay.

Qualitative and quantitative analyses of plankton were carried out during biomanipulation studies conducted in 1993-1996 in the Malta[n]ski Reservoir (64 ha, mean depth 3.1 m), Poland. The taxonomic composition and size fractions of phytoplankton, as well as number and biomass of phyto-, zoo- and bacterioplankton, were investigated. Despite the removal of all fish before the experiment and extensive stocking with predatory fish, attempts to biomanipulate a top-down control of phytoplankton in the Malta[n]ski Reservoir were not successful except for the first season. Macrozooplankton filtration (including cladocerans and calanoids) was found to control the development of small organisms only, such as pico-, nano- and bacterioplankton. Microplankton were also under the influence of filter feeders, but these were not effectively eliminated. Zooplankton grazing stimulated the development of large phytoplanktonic organisms both by providing intermediate disturbances for their growth and by supplying them with nutrients released from grazed small-size organisms. A similar influence on micro- and nanophytoplankton was exerted by microzooplankton (including rotifers and nauplii). The presence of picophytoplankton and bacterioplankton, however, was positively correlated with microzooplankton number.

Using two- and three-dimensional video recordings, the steps involved in predation that lead to the differential vulnerability of three sympatric rotifer sibling species (Brachionus plicatilis, B. ibericus and B. rotundiformis) to a co-occurring, predatory, calanoid copepod (Arctodiaptomus salinus) were examined. Brachionus rotundiformis, the smallest prey tested, was the most vulnerable with the highest encounter rate, probability of attack, capture and ingestion, and the lowest handling time. Comparison of the results with those of a previous study shows that A. salinus is a more efficient predator than a co-occurring cyclopoid copepod (Diacyclops bicuspidatus odessanus) feeding on these same rotifer species. However, despite its higher capture rates, A. salinus seems to be less selective than D. b. odessanus based on attack distances and prey handling times. The differential vulnerability to both calanoid and cyclopoid copepod predation can help explain the coexistence and seasonal succession of these co-occurring rotifer species.

Phytoplankton and environmental conditions in Lake Washington, Seattle, Washington, are discussed from the perspective of dynamic relationships between taxon-specific growth rates and environmental variables. More than four decades of measurements permit inspection of conditions associated with net increase and decrease for 40 phytoplankton species or species groups. Reproducible patterns exist for growth responses to over 25 environmental factors including nutrient chemistry, physical variables, and herbivorous zooplankton species. There appear to be no more than six main modalities of response to environmental factors, and responses to chemical and physical variables show coherence across taxa. Diatoms show a near uniform positive growth response to abundant inorganic nutrients, cold and transparent water, deep mixing, and intolerance for virtually all zooplankton grazers. Many chlorophytes and cyanobacteria show equally uniform growth responses to chemical and physical variables, although their preferences are virtually opposite from the diatoms. They benefit from the presence of copepods but show highly specific growth rate responses to different cladocerans and rotifers. Growth rate variations among the diatoms sort out along gradients of resource and physical factors, but there is coherence to the rise and fall of multiple species. Among the other algal divisions, despite a common set of physical and chemical conditions that promote growth rates, the species do not increase and decrease together. Instead, the prevailing grazer community appears to shape the phytoplankton community by admitting only certain species from the large pool of contenders.

In most toxicity studies using Cladocera, bioassays are routinely done to determine median lethal concentration (LC50) or the responses to sublethal exposure. However, information on the patterns of recovery of cladocerans exposed to different concentrations of toxicants is scarce. This is important because cladocerans exposed to toxicants for a short duration may later recuperate under favourable conditions. Using the life table demographic and population growth, the present study was conducted to evaluate the recovery patterns of Monia macrocopa exposed to five different concentrations ( 0, 25, 50, 75 and 100% of 24 h LC50 for CdCl2 or methyl parathion) and then returned to toxicant-free medium containing alga ( Chlorella vulgaris) at low (0.25 x 10(6) cells ml(-1)), medium (0.5 x 10(6) cells ml(-1)) or high ( 1 x 10(6) cells ml(-1)) levels. We measured selected life history variables such as average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase. Results indicated that regardless of food concentration, surviving individuals of M. macrocopa exposed to a median lethal concentration did not recover. The effect of food level was significant at 25 and 50% of the median lethal concentration for cadmium or methyl parathion. Age-specific fecundity curves showed that exposure to either toxicant for a duration as short as 24 h at one-fourth of the LC50 showed reduced output of offspring, especially at a lower food level. At and above exposures of 0.037 mg l(-1) of methyl parathion, no reproduction occurred. The highest gross and net reproductive rates ( 127 and 55 offspring female(-1)) were obtained in controls at the high ( 1 x 10(6) cells ml(-1)) algal food level. The rate of population increase obtained from life table data was around 0.7 per day in controls but decreased when exposed to toxicant concentrations. The rates of population increase per day derived from population growth data varied from 0.22 to 0.33 per day for the controls, depending on the food levels.

Partial 18S rRNA gene sequences of four macrodasyid and one chaetonotid gastrotrichs were obtained and compared with the available sequences of other gastrotrich species and representatives of various metazoan phyla. Contrary to the earlier molecular data, the gastrotrich sequences did not comprise a monophyletic group but formed two distinct clades, corresponding to the Macrodasyida and Chaetonotida, with the basal position occupied by the sequences of Tetranchyroderma sp. and Xenotrichula sp. respectively. Depending on the taxon sampling and methods of analysis, the two clades were separated by various combinations of clades Rotifera, Gnathostomulida, and Platyhelminthes, and never formed a clade with Nematoda. Thus, monophyly of the Gastrotricha is not confirmed by analysis of the presently available molecular data.

Rotifers of the asexual class Bdelloidea are unusual in possessing two or more divergent copies of every gene that has been examined. Phylogenetic analysis of the heat-shock gene hsp82 and the TATA-box-binding protein gene tbp in multiple bdelloid species suggested that for each gene, each copy belonged to one of two lineages that began to diverge before the bdelloid radiation. Such gene trees are consistent with the two lineages having descended from former alleles that began to diverge after meiotic segregation ceased or from subgenomes of an alloploid ancestor of the bdelloids. However, the original analyses of bdelloid gene-copy divergence used only a single outgroup species and were based on parsimony and neighbor joining. We have now used maximum likelihood and Bayesian inference methods and, for hsp82, multiple outgroups in an attempt to produce more robust gene trees. Here we report that the available data do not unambiguously discriminate between gene trees that root the origin of hsp82 and tbp copy divergence before the bdelloid radiation and those which indicate that the gene copies began to diverge within bdelloid families. The remarkable presence of multiple diverged gene copies in individual genomes is nevertheless consistent with the loss of sex in an ancient ancestor of bdelloids.

DNA sequencing has shown individual bdelloid rotifer genomes to contain two or more diverged copies of every gene examined and has revealed no closely similar copies. These and other findings are consistent with long-term asexual evolution of bdelloids. It is not entirely ruled out, however, that bdelloid genomes consist of previously undetected pairs of sequences so similar as to be identical over the regions sequenced, as might result if bdelloids were highly inbred sexual diploids or polyploids. Here, we employ fluorescent in situ hybridization with cosmid probes to determine the copy number and chromosomal distribution of the heat shock gene hsp82 and adjacent sequences in the bdelloid Philodina roseola. We conclude that the four copies identified by sequencing are the only ones present and that each is on a separate chromosome. Bdelloids therefore are not highly homozygous sexually reproducing diploids or polyploids.

The aim of the present study was to compare the sensitivity of 17 acute bioassays of cyanobacterial toxicity by assessment of crude extracts of three cyanobacterial samples (all dominated by Microcystis sp. but substantially differing in microcystin-LR content). Toxicity of the fractions prepared by solid-phase extraction (SPE) for microcystins was also determined. The most sensitive bioassay was the 24-h test with crustacean Thamnocephalus platyurus, which elicited high lethality in the samples and also in fractions without microcystins. The fruit fly Drosophila melanogaster, protozoans Spirostomum ambiguum and Tetrahymena termophyla, and the crustacean Daphnia pulex formed the second group of sensitive bioassays. Good selective toxicity response to microcystins also was observed in the weakly sensitive biotests with the oligochaete Tubifex tubifex and the rotifer Brachionus calyciflorus. Preconcentration of microcystins by SPE substantially decreased variation of the results in bioassays and improved the discriminating potential of most assays employed. (Copyright 2004 Wiley Periodicals, Inc.)

A comparison was made of growth performance in bullfrog Rana catesbeiana tadpoles and biogenic capacity in culture tanks with gravel, sand and hard bottoms. Stage 25 (Gosner) tadpoles from a single cohort were stocked in 1-m super(2) fibreglass tanks at 50 m super(-2). Two treatments and a control were employed, with three replicates each: T sub(1)=tadpoles reared in tanks with 0.02 m deep layer of sterilized silica gravel (2360 mu m particle size); T sub(2)=tadpoles reared in tanks with 0.02 m deep layer of sterilized beach sand (250 mu m particle size); and C=a control treatment with tadpoles reared in tanks with no soft substrate (conventional method). Tadpoles were fed on a 40% protein, powdered specific bullfrog feed at 13% body weight day super(-1). Results for survival, timing to metamorphosis, specific growth rate and weight gain exhibited no statistical differences between treatments (P>0.05). However, tadpoles in T sub(1) had an apparent overall better performance based on numerical indicators. Biotic colonization was also statistically similar (P>0.05) between treatments, showing an overall poor biogenic capacity for the tested substrates. Only three taxa, at low abundances, were recorded for phytoplankton and phytobenthos: cyanophiceae, chlorophyceae, and bacillariophyceae. Zooplankton was represented by two microinvertebrate groups, rotifera and protozoa. The statistical similarities between treatments may reflect that bullfrog tadpoles do not exploit naturally occurring aquatic biota when sufficient suspended artificial feed particles are present.

The effects of natural and anthropogenic factors on the vertical distribution of zooplankton benthic eggs of the sediments were analysed in the estuaries of Bilbao and Mundaka, both located in the Bay of Biscay. These estuaries differ largely in their pollution level, so in the estuary of Bilbao the human impact by physical perturbation (canalisation, dredging... ) and by introduction of pollutants (urban and industrial wastes) have been considerably greater than in Mundaka. Core samples were obtained in the intertidal soft sediments at the middle zone of each estuary using a hand core sampler 2 m length. Sediments grain size composition, and organic matter, chloropigments, lipid, carbohydrate and protein contents were analysed. Eggs were extracted from the sediment and their age was estimated by means of super(210)Pb and super(137)Cs analyses. Results showed that the benthic eggs abundance, composition and vertical distribution differed largely between estuaries. The total density of eggs recovered from the sediment was on average one order of magnitude higher in the estuary of Mundaka (10 super(5) eggs m super(-2)) than in the estuary of Bilbao (10 super(4) eggs m super(-2)), in which sediments anthropogenic organic enrichment was evident. Rotifer eggs dominated in Bilbao and calanoid copepod eggs in Mundaka, in agreement with the actual dominance of rotifers and calanoids in their estuarine zooplankton communities. In the estuary of Mundaka, benthic eggs and the majority of environmental variables were closely related to depth, calanoid eggs decreasing with depth while rotifer eggs increased. The results on super(210)Pb and the super(137)Cs allow us to know the date of the sediment layers, and to estimate at around 100 years the entire sequence analysed. Calanoid eggs dominated in recent sediments and rotifer eggs in older ones suggesting noticeable changes in the zooplankton community during the last century. In contrast, the age estimation was difficult in the estuary of Bilbao because super(210)Pb and super(137)Cs values indicated that more recent sediments were mixed with older sediments. This indicates that sedimentary processes are strongly affected by the human physical perturbation of sediments probably due to the periodical dredging and intense navigation in the estuary, and accounted for the rather homogeneous distribution of eggs with depth.

Phytoplankton often develop various defense mechanisms in response to zooplankton grazing, such as spines and colonies. While it is now known that increased spine length and cells in a colony of members of the genus Scenedesmus, when zooplankton grazing is intense, helps in reducing zooplankton filtering rates, the effect of these defense mechanisms at the population level has been observed in few studies. Here we present data on the growth rates of four zooplankton species, Brachionus calyciflorus, B. patulus, Ceriodaphnia dubia and Daphnia pulex at two food levels using two species of colony-forming Scenedesmus spp.: S. acutus (cell length = 18.2 +/- 0.4 mum; width = 4.2 +/- 0.1 mum; average colony length = 90 mum; width: 21 mum) and S. quadricauda (cell length: 21 +/- 0.5 width 7.5 +/- 0.3 mum; average colony length: 84 mum; width: 30 mum). Whereas S. acutus had no spines, S. quadricauda had spines of 6-10 mum. Population growth experiments of the test rotifers and cladocerans were conducted in 100 ml containers with 50 ml of the medium with test algae. Algae concentrations used were: 13 and 52 mg dw l(-1) of each of the two algal species offered in colonial forms. We used an initial inoculation zooplankter density of 1 ind. ml(-1) for either of the rotifer species and 0.2 ind. ml(-1) for either of the cladoceran species. In all, we had 64 test containers (4 test species of zooplankton x 2 test species of algae X 2 algal densities x 4 replicates). We found a significant effect of algal size on the growth rates of all the four tested species of zooplankton. The population growth rates of zooplankton ranged from - 0.58 to 0.66 and were significantly higher on diet of S. acutus than of S. quadricauda. Thus, our study confirms that the larger colony size and the formation of spines in S. quadricauda were effective defenses against grazing by both rotifers and smaller sized cladoceran Ceriodaphnia dubia but that larger-bodied Daphnia pulex could exploit both the algal populations equally.

In earlier single-species toxicity tests we showed the negative effects on the calanoid copepod Acartia tonsa upon exposure to cypermethrin, a pesticide used in treatment for sea lice in salmon farming. In the present study we assessed effects at a higher level of biological organization and under a more realistic exposure scenario using mesocosms. The results showed that simulated field studies (SFSs) could be conducted with the mesocosms designed here. When cypermethrin was applied inside these mesocosms, its concentration decreased exponentially following a first-order kinetics model. The pesticide immediately reduced zooplankton density and biodiversity not only directly, by killing copepods, but also indirectly, by increasing the numbers of rotifers. Zooplankton density recovered after treatment, but zooplankton biodiversity remained altered. In an open environment, however, the rapid dissipation of the pesticide, coupled with population processes of compensation, migration, and immigration, may lead to recovery of the affected zooplankton communities.

Brachionus plicatilis are used as live prey for rearing winter flounder larvae at first feeding. This rotifer is grown between 20 and 25 degree C (its optimal growth temperature) and then introduced into the 10 degree C water in which larvae are reared. The rapid thermal difference between the two media is thought to reduce B. plicatilis quality and consequently affect larval rearing efficiency. In order to optimize larval rearing, a study was conducted to compare the effects of two different diets on larval growth performance and nutritional condition: (1) larvae fed B. plicatilis reared at 24 degree C and (2) larvae fed B. plicatilis reared at 24 degree C but acclimated overnight at 10 degree C. Comparisons were undertaken using morphometric measurements, nucleic acid (RNA /DNA) ratios, total protein content, trypsin activity, and triacylglycerol/sterol ratios. Fatty acid composition of larvae was also studied with a focus on the levels and ratios of three essential fatty acids (docosahexaenoic acid or DHA, eicosapentaenoic acid or EPA, and arachidonic acid or AA). Unique information regarding trypsin activity and lipid components (phospholipid, triacylglycerol, and sterol) of winter flounder larvae is provided in this study. Trypsin activity was detected very early in larvae and was not affected by acclimation of prey. Phospholipid, triacylglycerol, and sterol composition showed no significant difference between the two diets tested and was characterized by high phospholipid content as well as low triacylglycerol and sterol contents. EPA, DHA, AA, DHA/EPA, and DHA /AA decreased from days 12 to 26. Interestingly, DHA content was significantly higher in larvae fed acclimated rotifers and AA content decreased significantly in 26-day-old larvae fed acclimated B. plicatilis. Overall results indicate that overnight acclimation of B. plicatilis at 10 degree C is not important for optimizing the rearing of winter flounder larvae although it does influence the fatty acid composition.

Twenty four species (19 Rotifera, 4 Cladocera, 1 Copepoda) were recorded in the. zooplankton of Lake Koroneia from June 1999 to June 2000. The dominant species were the Cladocera Daphnia magna and the rotifers Brachionus dimidiatus and B. rubens. Total abundance ranged from 13 to 32,426 ind. L-1 and its seasonal dynamics resembled those of hypertrophic lakes, but attaining much higher numbers due to the absence of predation pressure from fish. Rotifers prevailed (up to 100%) during the warm months (June-October) and their seasonal dynamics were governed by temperature and the presence of large Daphnia individuals. Cladocera were absent during the slimmer due to high pH values (9.32-11.10) and/or the composition of the phytoplankton community where Anabaenopsis milleri prevailed.

We evaluated fertilizer effects on phytoplankton and zooplankton concentrations in channel catfish Ictalurus punctatus nursery ponds. In 2001, three ponds were not fertilized and three ponds were fertilized with inorganic (8.4 kg/ha N, 2.0 kg/ha P followed by twice a week applications at half the initial rate) and organic fertilizer (224 kg/ha cottonseed meal followed by once a week applications of 28 kg/ha) for 4 weeks. Total P and soluble reactive P (SRP) were significantly higher in fertilized ponds (P0.05), however no differences in algal populations resulted. Of the zooplankton, only copepod nauplii were higher in fertilized ponds. In 2002, 26 ponds were used. Sixteen ponds were newly constructed; 10 ponds were old (>10 years). Within each age group, treatments of no fertilizer (controls), organic fertilizer only, inorganic fertilizer only, or both organic and inorganic fertilizers were used for 3 weeks. In 2002, the same P but higher N rates were used (20.2 kg/ha N followed by twice a week at half rate). Several differences occurred among treatments (P0.05). Both total P and total N were significantly higher in ponds fertilized with inorganic fertilizer and both inorganic and organic fertilizers than in control ponds and organically fertilized ponds. Also, total P, total N, SRP, and nitrite were all significantly higher in old ponds than in new ponds. All phytopigment concentrations were also higher in old ponds than in new ponds. Chlorophyll a (total algal biomass), lutein (green algal biomass), and fucoxanthin (diatom biomass) were significantly higher in ponds fertilized with inorganic fertilizer or both inorganic and organic fertilizers than in control or organically fertilized ponds. Old ponds contained significantly more rotifers, copepod adults, and ostracods than new ponds. Rotifer and ostracod concentrations were not different among fertilizer treatments. Copepods adults and nauplii were significantly increased in ponds fertilized with both organic and inorganic fertilizers than in organically fertilized ponds. Cladocerans were significantly higher in inorganically fertilized ponds than in all others. Results indicated little benefit of organic fertilizer addition at the rates used. Also, ponds appear to be more N limited than P limited. Old ponds are more fertile than new ponds. Applying only inorganic fertilizer at an initial rate of similar to 20 kg/ha N and 2 kg/ha P, followed by subsequent applications of half the initial rate for 3-4 weeks increased zooplankton concentrations desirable for fry with larger mouth gapes.

The species composition of zooplankton and its variability were studied with all integrated water-sediment analysis for a period of two years in a hypersaline temporary pond in SE Italy. The basin was affected by extended drought during summer, and even during the wet period the sodium chloride salinity was never below 42.5parts per thousand The zooplankton showed the presence of seasonal species (mainly Anostraca), together with not seasonal, but opportunistic ones (mainly Rotifera, and Ciliophora) with a shorter life cycle. Rotifers (mainly Hexarthra fennica, and Proales similis), and ciliates (Fabrea salina) attained 99-100% of total planktonic organisms in certain periods. Resting stages were extracted from the upper 6 cm of 14 sediment cores collected during a dry period (August 1998). A total of 24 resting morphotypes (cysts) were listed-more than double the number of the active organisms (11) found in the plankton over the two years. The seasonal succession of species was different in the two years Studied. This fact, together with the richness of the cyst bank of the sediment, indicates that in each period the water Column shows only a portion of the biodiversity, which the sediment contains Unexpressed as resting stages. The Study of cyst distribution (both horizontal and vertical) in sediments provided complementary suggestions to understand the space-time distribution of the plankton organisms. Laboratory tests showed that hatching of different cysts generally occurred in a wide range of salinity conditions, and was not synchronous. This allowed US to assume that even the cyst hatching rate Could be an adaptation to highly variable extreme environments.

Musculature and nervous system of Gnathostomula peregrina (Gnathostomulida, Scleroperalia) were reconstructed from whole animals by immunohistochemistry and confocal laser scanning microscopy. The F-actin muscular subset, stained with FITC-labeled phal-loidin, consists of: (1) eleven pairs (four ventral, one ventrolateral, one dorsolateral, five dorsal) of longitudinal muscles; (2) two types of diagonal muscles (thin fibers throughout the body, and slightly thicker fibers of which seven pairs occur ventrally and two pairs dorsally); (3) evenly spaced thin circular fibers that gird the posterior half of the body, continuing less prominently into the anterior half; and (4) a complex pharyngeal and genital musculature. Dorsoventral muscles are absent. The organization of the FMRFamidergic nervous system shows: (1) a central nervous system with a frontal ganglion and one pair of longitudinal nerves ending in a terminal commissure. and one median ventral nerve; (2) eight to ten unipolar perikarya above, and up to ten bipolar perikarya in front of the brain; (3) a total of five (one unpaired, two paired) longitudinal nerves of the peripheral nervous system with two to four accompanying perikarya; and (4) a buccal ganglion of the stomatogastric nervous system with six to eight perikarya above the pharyngeal bulbus. Our results reveal the musculature and nervous system of Gnathostomida to be more complex than hitherto reported.

We quantified the life history variables of M. macrocopa subjected to different treatments such as high temperature, epizoic infestation by the rotifer Brachionus rubens, periodic starvation and exposure to sublethal levels of cadmium using the life table demography method. These were compared against a treatment of Chlorella vulgaris offered at a concentration of 1 x 10(6) cells ml(-1) and set at 25 +/- 1 degreesC, which served as the control. The effect of a diet of the colonial form of Scenedesmus quadricauda was compared against a diet of S. quadricauda as single cells, which acted as control. For each treatment the experimental design consisted of four cohorts of 20 neonates. Using standard life table demographic methods, we quantified average lifespan, gross and net reproductive rates, generation time and the rate of population increase. Except for the study on temperature effects, all experiments were conducted at 25 degreesC. For the temperature experiments we exposed the test cladocerans to 35 degreesC with the algal density and type being identical to the controls. To study the effect of starvation, we starved the test individuals for 8 h before offering Chlorella every day. Cadmium toxicity was evaluated using 0.04 mg l(-1), as nominal concentration of CdCl2. Among the life history variables studied, the rate of population increase was the most sensitive, being influenced significantly by the stress factors studied. The responses of M. macrocopa subject to different conditions have been interpreted in terms of the life history strategies of M. macrocopa.

The toxicity of river water in the Lower Don basin was studied using biotesting with different biological objects. Water taken from most examined reaches of the Don and its tributaries was shown to exert toxic effect on crustaceans, algae, protozoa, and Rotifera.

Results of different approaches potentially useful for the evaluation of water ambient quality were analysed and compared in a small temperate lowland river with mixed diffuse and multiple-point source pollution. The Reconquista River (Buenos Aires Province, Argentina), one of the most polluted watercourses of Latin America, receives agrochemicals as well as domestic and industrial (mostly untreated) effluents. Physical and chemical water variables were determined; unispecies algal bioassays (with Chlorella pyrenoidosa and Scenedesmus acutus) were carried out in laboratory; and density and structure of phyto- and zooplankton were analysed at three sites in four dates (representing a range of likely conditions in the river). A general scheme of association among plankton, bioassays and physical/chemical variables was elaborated, that helped to infer possible control factors in this multi-stressed system. Some empirical methods, but mainly mathematical ones including multivariate techniques (as PCA, cluster analysis), were applied for evaluation of samples. A preliminary selection of indices and attributes as potential indicators of the water river quality was made, and then applied for assay a tentative integrative ordination of samples. The relative best water quality was recorded when-where dissolved oxygen concentration, algal diversity and planktonic crustacean density were higher. The worst water quality corresponded to the lack of cladocerans and lowest crustacean density, and higher: organic and industrial pollution, major nutrients (ammonium and orthophosphates), BOD, hardness, conductivity, algal biomass in bioassays, phytoplankton density (>10 000 ind. mL super(-1)), dominance of a single algal species (>90%), and rotifer proportion in zooplankton (>85%).

Lipid spray beads (LSB) composed singly or of mixtures of trilaurin, methyl palmitate (MP), menhaden stearine (MS), spermaceti and coconut oil were prepared and their performances were compared for delivering glycine and tyrosine to the early stages of fish larvae. Measures of performances of LSB included inclusion (IE), encapsulation (EE), retention (RE) and delivery efficiencies (DE) in addition to T50 (time to 50% retention) values. Tyrosine and both particulate and aqueous solutions of glycine were successfully incorporated within LSB using a melt-spray method, with incorporation efficiencies ranging from 81.0% to 91.1%. A maximum encapsulation efficiency of 21.0% was achieved for LSB composed of 100% MS with a core of particulate tyrosine. In order to modify their hardness, LSB containing particulate glycine were prepared with 100% MS with and without additions of coconut oil or spermaceti. Highest retention and delivery efficiencies were achieved by LSB composed of 100% MS, indicating that substitution of MS with coconut oil or spermaceti had no beneficial effects on LSB performance. LSB composed of 100% MS had a retention efficiency of 34% after I h of suspension, corresponding to a delivery efficiency of 0.523 mg glycine 10 mg(-1) lipid. LSB composed of 75% MS+25% spermaceti containing aqueous glycine had a significantly higher retention efficiency compared to that of LSB containing particulate glycine (P<0.05, Tukey's HSD). Furthermore, delivery efficiencies indicated that LSB (75% MS+25% spermaceti) containing an aqueous core delivered significantly higher concentrations of glycine (0.291 mg 10 mg(-1) lipid after I h suspension in water) compared to LSB with a core of particulate glycine. Tyrosine was better retained by LSB compared with glycine, probably due to differences in the water solubilities of these two amino acids. LSB (100% MS) containing 6.2% and 21.0% (w/w) of tyrosine had identical retention efficiencies indicating that higher tyrosine concentrations did not result in higher percent leaching rates. LSB (100% MS) containing 21.0% tyrosine had a T50 value of 654 min with a delivery efficiency of 1.10 mg tyrosine 10 mg(-1) lipid. Visual observations indicated that LSB composed of 50% MS + 50% coconut oil or 100% MS can effectively deliver nutrients to 3-day-old clownfish, Amphiprion percula, larvae. Particles in fecal strands and in guts of larvae were compacted, confirming the ability of larvae to form pellets from digested particles. Release of Poly-red was evident by a pink coloration in the lumen of the hindgut. LSB show promising potential for delivery of dietary amino acids to marine fish larvae. (C) 2004 Elsevier B.V. All rights reserved.

Brachionus havanaensis is a common rotifer in the North American continent. Its frequent occurrence in relatively high densities and availability throughout the year in several Mexican freshwater bodies prompted us to understand the population dynamics of this species in relation to food level (Chlorella vulgaris at 0.5X10 super(6), 1.0X10 super(6) and 2.0X10 super(6) cells ml super(-1)) and temperature (15 degree , 20 degree , and 25 degree C). We found that regardless of the temperature, an increase in food level resulted in an increase in the population growth of the rotifers. However, at any food level, rotifers cultured at 15 degree C did not increase beyond 8 ind. ml super(-1); on the other hand at comparable food concentrations at both 20 and 25 degree C, the population densities were higher than 600 ind. ml super(-1). The rate of population increase per day (d super(-1)) of B. havanaensis varied from 0.02 to 0.29 d super(-1) depending on the food density and temperature. Our results also showed that regardless of the food level, at 15 degree C B. havanaensis had no statistically significant relation between the number of eggs per female and the population abundance. On the other hand, significant inverse relationships were observed between the egg ratio and population density of B. havanaensis grown at 20 degree and 25 degree C, regardless of the food level. When the daily growth rates were plotted against the population densities of the previous day, we found a significantly inverse relation for rotifers grown at 20 degree and 25 degree C, but not at 15 degree C, for all tested food levels. There were statistically significant effects of food level, temperature, and the interaction of both parameters on both the peak population density and the rate of population increase, although temperature had a far greater influence than did food.

Brachionus havanaensis is a common rotifer in the North American continent. Its frequent occurrence in relatively high densities and availability throughout the year in several Mexican freshwater bodies prompted us to understand the population dynamics of this species in relation to food level (Chlorella vulgaris at 0.5X10(6), 1.0X10(6) and 2.0X10(6) cells ml(-1)) and temperature (15degrees, 20degrees, and 25degreesC). We found that regardless of the temperature, an increase in food level resulted in an increase in the population growth of the rotifers. However, at any food level, rotifers cultured at 15degreesC did not increase beyond 8 ind. ml(-1); on the other hand at comparable food concentrations at both 20 and 25degreesC, the population densities were higher than 600 ind. ml(-1). The rate of population increase per day (d(-1)) of B. havanaensis varied from 0.02 to 0.29 d(-1) depending on the food density and temperature. Our results also showed that regardless of the food level, at 15degreesC B. havanaensis had no statistically significant relation between the number of eggs per female and the population abundance. On the other hand, significant inverse relationships were observed between the egg ratio and population density of B. havanaensis grown at 20degrees and 25degreesC, regardless of the food level. When the daily growth rates were plotted against the population densities of the previous day, we found a significantly inverse relation for rotifers grown at 20degrees and 25degreesC, but not at 15degreesC, for all tested food levels. There were statistically significant effects of food level, temperature, and the interaction of both parameters on both the peak population density and the rate of population increase, although temperature had a far greater influence than did food.

Thermally assisted hydrolysis and methylation of cellular lipids, by means of Curie-point pyrolysis of intact whole cells in the presence of a quaternary ammonium hydroxide reagent, provided analytical access (pyrolysis-gas chromatography; Py-GC) to the very small amounts of algal carbon delivered by fluorescence-activated cell sorting. Based on differences in pigment composition, population-specific in situ fatty acid profiles could be obtained of the major taxa present in the phytoplankton of Lake Loosdrecht (The Netherlands). By combining Py-GC and compound-specific isotope-ratio mass spectrometry (Py-GC-IRMS) the in situ carbon isotopic signatures could be established of the fatty acid profiles retrieved by flow cytometry. Colonial phytoplankton not amenable to cell sorting and zooplankton specimens were also isotopically characterised with this technique by subjecting handpicked samples to pyrolytic methylation. In this way proxies could be obtained in great detail for isotopic end-members delineating important carbon sources and sinks in the pelagic food web of Lake Loosdrecht. These analyses suggested a significant isotopic heterogeneity among major representatives of the phytoplankton in Lake Loosdrecht. This heterogeneity was also reflected in the isotopic composition of the zooplankton, implying the occurrence of preferential grazing. A differential labelling of the phytoplankton using super(13)C-CO sub(2) in a laboratory confinement, and subsequent monitoring of label transfer to the zooplankton, corroborated selective feeding in some rotifer species. The large-bodied rotifer Asplanchna, previously thought to be predaceous, apparently mainly fed on algae rather than small rotifers, whereas Euchlanis dilatata actively selected filamentous cyanobacteria. Flow cytometric cell sorting in concert with Py-GC-IRMS offers new possibilities in carbon isotope-based food web studies.

The effects of light intensity on feeding incidence and prey consumption at first feeding of spotted sand bass larvae (Paralabrax maculatofasciatus Steindachner), using four light intensity treatments (0, 100, 400, and 700 lx) were evaluated. Specimens were fed the rotifer Brachionus plicatilis at a density of 3 rotifers mL super(-1). One hour after the addition of prey, 30 plus or minus 3 (mean plus or minus SEM) larvae were sampled from each treatment aquarium. Feeding incidence was evaluated as the percentage of larvae with prey in the digestive tract. Feeding intensity was measured as the number of prey in the digestive tract of the larvae. Histological analysis was carried out to describe the eye structure at the time of first feeding. Larvae fed in darkness (0 lx) had a significantly lower (P<0.05) feeding incidence (1.2 plus or minus 2.2%) and intensity (0.4 plus or minus 0.7 rotifers larvae super(-1)) than those larvae fed at 100 (28 plus or minus 11%, 1.8 plus or minus 0.2 rotifers larvae super(-1)), 400 (48 plus or minus 10%, 2.4 plus or minus 0.3 rotifers larvae super(-1)), and 700 lx (52 plus or minus 4%, 2.4 plus or minus 0.1 rotifers larvae super(-1)). Feeding incidence of the spotted sand bass larvae increased with light intensity while the feeding intensity showed no significant difference (P>0.05) between light treatments. Histological analysis of the eye structure showed that first feeding larvae had well-formed lens along with a retina composed of pure single cones as photoreceptors.

Seven aerially applied cotton herbicides and defoliants were tested for possible adverse impacts on pond phytoplankton and zooplankton and critical water quality variables. Treatments simulated direct spraying of ponds and high and low amounts of drift judged able to reach the pond, 1/10 and 1/100 direct rates, respectively. The study was conducted in twelve 500-l outdoor pool mesocosms filled with pond water from an adjacent goldfish Carassius auratus culture pond. Plankton and water quality samples were taken just prior to application and at 24 and 48 h after application. Sampling for chemicals showing effects were continued approximately weekly until oxygen levels in drift treatments returned to no significant difference from control. Chemicals tested and direct rates (kg active ingredient ha super(-1)) were diuron as herbicide (1.4), paraquat (0.83), quizalofop (0.05), dimethipin (0.15), diuron as defoliant (0.1675), ethephon (0.176), tribufos (0.99) and sodium chlorate (5.28). Except for the diuron compounds, the cotton herbicides and defoliants produced no measurable impacts on pond plankton or associated water quality. Following application on March 5 of diuron, used as an herbicide, chlorophyll a levels and photosynthesis were significantly depressed in relation to diuron concentration. Recovery occurred slowly, and at the high drift dosage by week 3 morning oxygen levels returned to near control levels, although chlorophyll a levels were 1/3 the control. However, the off-flavor cyanobacterium, Anabaena laevendri, was essentially eliminated by week 3; and pH and thus un-ionized ammonia were much lower in high drift treatments. Copepod adult and nauplii zooplankton levels were depressed at week 2. However, rotifer numbers increased in the low drift treatment in weeks 3 and 4 and those of copepod nauplii in week 3. Fall application of diuron, as a defoliant at 1/10 the spring rate, produced similar effects when compared by concentration. The main adverse impact of diuron drift is on dissolved oxygen levels and can be anticipated by provision of adequate aeration capacity.

This study documents for the first time both vertical and horizontal distribution patterns of the zooplankton community in Lake Kinneret during the period of thermal stratification. The zooplankton distribution patterns were explored in relation to abiotic (temperature, oxygen) and biotic (picocyanobacteria, ciliates, flagellates, phytoplankton, fish) environmental gradients. Sampling was carried out on 6-7 July 1992 at five stations and six depths from nearshore to offshore. Zooplankton abundance and biomass varied from 5 to 267 ind. l super(-1) (mean: 95 ind. l super(-1)), and from 0.1 to 65 d.w. mg m super(-3) (mean: 24 d.w. mg m super(-3)). Zooplankton taxonomic groups (Rotifera, Cladocera, Cyclopoida, Calanoida) and size classes (micro-, meso- and macrozooplankton) showed peaks of maximal density and biomass in the epilimnetic and metalimnetic strata (5 and 14 m). Depth, accounting for 31-39% of total spatial variation, reflected the vertical distribution of zooplankton in relation to temperature and oxygen declines, and the higher concentration of food resources (protists and phytoplankton) in the epilimnion and metalimnion. Onshore-offshore distance, accounting for 17-22% of the total spatial variance, reflected different distribution patterns shown among zooplankton groups and size classes. The macrozooplankton (Copepoda, Cladocera) was more abundant offshore, whereas microzooplankton (Rotifera and nauplii) predominated nearshore. These horizontal distribution patterns were related to small increases in temperature and phytoplankton biomass, and higher concentrations of fish in the littoral zone. Although limited to a short temporal scale, our study indicated that zooplankton spatial distribution in Lake Kinneret during the period of thermal stratification was related to physicochemical, food and predation factors, manifested differently along the vertical and nearshore-offshore gradients.

This paper presents a mathematical model of interactions between two herbivorous invertebrates (ciliate Paramecium caudatum and rotifer Brachionus plicatilis) and two planktonic algae (Chlorella vulgaris and Scenedesmus quadricauda) spatially segregated in two compartments of a chemostat - type experimental microcosm system. The model mimics a "producer-consumer" aquatic biotic cycle, describing the dynamics of the mixed culture of ciliates and rotifers, as "consumer" compartment, feeding on the mixed algal culture, as "producer" compartment, under N-limiting conditions. We experimentally found that metabolites of the alga Scenedesmus produce an adverse effect on the reproduction of ciliate Paramecium. Taking this effect into account improved the behavior of the model, the results of which came into qualitative agreement with the experimental results. Both our experimental and modeling approaches demonstrated that, even in conditions of a spatially - segregated "producer-consumer" biotic cycle, species coexistence is impossible either in the mixed algal culture or in the mixed invertebrate culture. Scenedesmus excluded Chlorella, whereas Brachionus excluded Paramecium.

An experimental investigation was carried out, and a mathematical model of interaction between invertebrates (infusoria Paramecium caudatum and rotifera Brachionus plicatilis) and algae (Chlorella vulgaris and S enedesmus quadricauda) in the <> aquatic biotic cycle with spatially divided links was constructed. The model describes the dynamics of a mixed culture of infusoria and rotifera in the <> link, when they consume a mixed culture of algae coming from the <> link. A negative influence of products of algae Scenedesmus metabolism upon the reproduction of infusoria P. caudatum was revealed. Taking this into account, a qualitative coincidence of the results of mathematical modeling with experimental data was obtained. It was shown that the co-existence of mixed algae culture in the <> link with invertebrates in the <> link in the <> aquatic biotic cycle is impossible because of the displacement of infusoria P. caudatum by rotifera Brachionus plicatilis.

An experimental investigation was carried out, and a mathematical model of interaction between invertebrates (infusoria Paramecium caudatum and rotifera Brachionus plicatilis) and algae (Chlorella vulgaris and Scenedesmus quadricauda) in the producer-consumer aquatic biotic cycle with spatially divided links was constructed. The model describes the dynamics of a mixed culture of infusoria and rotifera in the consumer link, when they consume a mixed culture of algae coming from the producer link. A negative influence of products of algae Scenedesmus metabolism upon the reproduction of infusoria P. caudatum was revealed. Taking this into account, a qualitative coincidence of the results of mathematical modeling with experimental data was obtained. It was shown that the co-existence of mixed algae culture in the producer link with invertebrates in the consumer link in the producer-consumer aquatic biotic cycle is impossible because of the displacement of infusoria P. caudatum by rotifera Brachionus plicatilis.

One of the pathways for the entry of bacteria, both pathogenic and probiotic, into the larvae of fish hatcheries is via live prey. As a preventive measure against infections, live prey may be cultured, supplementing the food with probiotics. Some lactic acid bacteria (LAB) have been successfully used in the larviculture. In this study, the nutritional effect of seven terrestrial LAB has been studied regarding the growth of the rotifer Brachionus plicatilis. The cultures were carried out without partial renewal of the culture medium, feeding the rotifers on baker's yeast and adding some of the species of bacteria. In all cases, the addition of the bacteria increased both the specific maximum growth rate and the maximum density obtainable in the cultures. However, the best results were obtained with the addition of Lactococcus casei ssp. casei, Pediococcus acidilactici, or Lactobacillus lactis spp lactis. The rates of growth obtained with the individual or joint addition of these three bacteria were 8-13 times greater than those obtained with the control cultures after 4-5 days' culture. In this study, a series of kinetic models has been applied (logistic modified-Gompertz, logistic-logistic, and generalised logistic) which describes the experimental data, obtaining a set of parameters of biological significance which facilitate the optimisation of the use of these bacterial strains in the mass production of rotifers.

We counted rotifers within lobules of an epiphytic liverwort (Frullania eboracensis subs. eboracensis). Of 81 plants marked in the summer of 2001, 44 were female, 17 male, and 20 nonexpressing. Nonexpressing plants were significantly smaller than expressing plants. An ANCOVA revealed a non-significant or marginally significant tendency for the proportion of rotifer-occupied lobules to differ among male, female, and nonexpressing plants (p less than or equal to 0.09). Nonexpressing plants tended to have the greatest proportion of occupied lobules. We hypothesized that nonexpressing plants were younger than expressing plants. We investigated this pattern further by sampling from the interior and the edges of plants, knowing that the exterior of the plant is younger than the interior. In two separate experiments on different plants, a significantly greater proportion of exterior than interior lobules contained rotifers.

Mercury is highly toxic to a variety of aquatic organisms including zooplankton. The functioning of freshwater ecosystems can be altered if rotifers, being a natural food link between phytoplankton and fish larvae, are contaminated by mercuric compounds. In order to detect age-specific responses of the rotifer Brachionus calyciflorus to mercury toxicity ( 5 nominal concentrations as chloride viz. 0, 0.000625, 0.00125, 0.0025 and 0.005 mg l(-1)), we used the standard life table method at two different food ( Chlorella vulgaris) levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1)). Data indicated that increase in mercury concentration had an increasingly intense negative effect on many of the life history variables, while at higher food levels, its impact was less. A nearly rectangular survivorship pattern was obtained in controls, especially at higher food levels. This trend gradually changed to a steep fall as the concentration of the heavy metal in the medium increased from 0 to 0.005 mg l(-1). At any given food density, increase in the mercury concentration resulted in decreased age-specific reproduction. A maximum of 3.5 offspring female) 1 was observed in controls at higher food density. The average lifespan varied from 6 to 8 days at low food level, depending on the heavy metal concentration in the medium. The corresponding values at high food level varied from 8 to 12 days. Regardless of mercury concentration in the medium, gross and net reproductive values varied from 10 to 33 and 4 to 19 offspring female(-1). The longest generation time ( about 9 days) of B. calyciflorus was obtained at 1.5 x 10(6) cells ml(-1) food density in control, while the shortest was 5 days at low food level and high (0.005 mg l(-1)) mercury concentration in the medium. Depending on the food level and heavy metal concentration in the medium, the rate of population growth (r) varied from 0.32 to 0.62 d(-1). In general, higher food level resulted in higher r. Except generation time, all other derived variables were significantly influenced by food level and the heavy metal concentration in the medium.

Copepod predation on rotifers affects the dynamics and structure of zooplankton communities. Many experimental studies have analysed the feeding behaviour of some calanoid and cyclopoid copepod species on different rotifer prey types. However, considerations of the impact of predation by these invertebrates on rotifer populations have generally neglected possible additional effects of this predation through differential predation mortality between eggs, egg-bearing females and females without eggs. The present study used direct observations to describe the predatory effect of two freshwater copepod species, Lovenula alluaudi (Calanoida) and Acanthocyclops vernalis (Cyclopoida), on egg-bearing females of the rotifer Keratella cochlearis. Both copepod species ingested Keratella eggs and egg-bearing females, i.e. the female plus its egg. However, in the case of the calanoid copepod, there was a significantly greater probability of suppression of Keratella eggs after capture, including direct predation and separation of the eggs from their mothers, than of Keratella females plus attached eggs. In contrast, the probability of suppress:ion of Keratella eggs by the cyclopoid copepod did not significantly differ from that of whole Keratella females. These results are discussed in terms of the impact of this predation pattern on the fecundity of K. cochlearis populations in natural ecosystems. Rotifer reproduction may be regulated not only by food availability but also by copepod predation.

Peritrich epibiont protozoans and metazooplankton (rotifers, cladocerans and copepods) were investigated seasonally in a shallow eutrophic artificial reservoir in a subtropical region (Monjolinho Reservoir, Brazil). The ciliated peritrichs Rhabdostyla sp. and Scyphidia sp. were found to colonize individuals of different metazooplanktonic groups, especially copepods (47.20% of the total number of metazooplanktonic organisms found with epibionts and 57.14% of infection in the copepod population). Copepods also had the greatest epibiont load, followed by cladocerans and rotifers. Rotifers were the most important metazooplanktonic group (90.14% of the total) and the taxa observed with epibionts were Filinia longiseta, Polyarthra, Brachionus and Keratella, with highest preference for the first organism. F. longiseta was present at low density compared with the others and the preference as a substrate for epibionts may be related to its type of adhesion surface (soft) and/or feeding habits (particle feeding).

Sediments from the Atlantic coast of Spain have been studied to evaluate environmental quality by using an integrated approach including chemical and toxicological data. Sediment samples were collected in four littoral ecosystems located in Spain, Bay of Cadiz, Guadalquivir River estuary, Ria of Huelva, and Ria of Coruna. To characterize the sediments, organic carbon, granulomere content, total sulfide, eight trace metals (Hg, Cd, Pb, Cu, Zn, As, Ni, and Cr), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) were measured. The toxicity of sediments was assessed with the amphipod Ampelisca brevicornis, the clam Ruditapes philippinarum, juveniles of the fish Solea senegalensis, populations of the estuarine rotifer Brachionus plicatilis, and populations of the bacterium Vibrio fischeri (Microtox). The results obtained show that in general, stations located in the Ria of Huelva were associated with heavy metal contamination and with the highest toxicity. Only chronic toxicity tests were capable of identifying the effects associated with PCB concentrations. The sediment quality guidelines calculated by means of a multivariate analysis approach for contaminants not associated with biological effects (mg/kg) are Hg, 0.54; Cd, 0.51; Pb, 260; Cu, 209; Zn, 513; As, 27.4; and total PCBs, 0.05.

Here we report the effect of food concentration on the recovery from anhydrobiosis of a bdelloid rotifer, Macrotrachela quadricornifera. Cohorts were either starved. or fed high or low concentrations of food, before being dried and their subsequent recovery rates determined. The rotifers starved for 3 d before anhydrobiosis recovered in significantly higher proportion, and those fed lower food concentration recovered better than those fed higher food concentration. In addition, starvation did not decrease the recovery of other bdelloid specie's (Philodina roseola and Adineta sp.1) which were either fed or starved before anhydrobiosis. These results suggest that a successful recovery from anhydrobiosis is not dependent on prior resource level supplied to the bdelloids. However. the lack of resources might not be the only factor in a successful recovery from anhydrobiosis. Observations using scanning electron microscopy of fed individuals of M. quadricornifera entering anhydrobiosis showed that some food remained in the digestive tract. Thus, we propose that the negative effect of rich food may be due to a purely mechanical effect and may be interfering with a proper folding of the rotifer body at the onset of anhydrobiosis. This contribution results from studies carried out in preparation for biological experiments scheduled on the International Space Station (ISS).

Mitochondria play an essential role in metabolism. Comprising its own circular DNA, the mitochondrial genome of metazoans typically encodes 2 rRNAs, 22 tRNAs, and 12 to 13 polypeptides. These polypeptides are responsible for the production of protein complexes in the inner mitochondrial membrane that facilitate the production of ATP. Based upon genomic similarities, eukaryotic mitochondria may have evolved from an alphaproteobacterium-like ancestor. A mitochondrial genomics study was initiated using organisms from invertebrate phyla including Priapulida (Halicryptus spinulosus), Rotifera (Encentrum tectipes), Acanthocephala (Echinorynchus gadi), Gnathostomulida (Gnathostomula peregrini), Cycliophora (Symbion pandora), and Nematoda (Oscheius tipulae and Rhabditoides regina). Gene regions from cytochrome c oxidase I (coxI), cytochrome b, 12S rRNA and 16S rRNA were amplified and sequenced using universal primer pairs. Nested primers were then designed to amplify larger fragments of each mitochondrial genome. Nested PCR products (5-10 kb) were obtained from three organisms, which covered 50%-75% of the genomic mtDNA in highly purified form. These products will be subjected to shotgun sequencing. Further PCR studies of the remaining fragments, as well as those of other mitochondrial genomes, are ongoing. Successful amplification of coxI sequences using LCO/HCO primers was achieved from all invertebrates studied. Cytochrome c oxidase, the terminal oxidase in the respiratory chain, reduces oxygen to water through electron and proton transfer. The PCR of the coxI from the rotifer (E. tectipes) sample yielded two divergent protein-coding sequences. BLAST analyses revealed one to be most closely related to other rotifer coxI sequences. The second sequence appears equally related to coxI genes from alphaproteobacteria (e.g., Rickettsia) and from various eukaryotes, suggesting that this gene and its associated genome could be in an interesting phylogenetic position.

Nutrient and fish manipulations in mesocosms were carried out on food-web interactions in a Mediterranean shallow lake in south-east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear-water states. Planktivorous fish increased concentrations of soluble reactive phosphorus. Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L super(1) PO sub(4)-P and 0.6 mg L super(1) NO sub(3)-N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. Declining water levels during summer favoured plant-associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. The thresholds of nutrient loading and in-lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality

This study aimed to evaluate the influence of different volumes of supplemented carbon dioxide, which is a potential donator of carbon atom, on the fatty acid profile of four microalgae strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd, Nannochloris atomus Butcher and Isochrysis sp.) currently used to enrich rotifers fed to marine fish larvae during two different phases of growth (logarithmic and stationary). Half of the microalgae were cultured at a low CO sub(2) concentration (0.5 L/min), corresponding to 1% the air volume (0.038 L/min per L of culture) and the other half of microalgae were cultured at a high concentration of CO sub(2) (1.1 L/min), corresponding to 2% the air volume (0.086 L/min per L of culture). The resulting fatty acid profile was species-specific and Nannochloris atomus appeared less suitable for marine organism feeding because of its high percentage of alpha-linolenic acid which represents the only n-3 PUFA of this alga (28.7%). On the contrary, Isochrysis sp. showed the largest proportions of n-3 PUFA also when maintained in the stationary phase (36.46%). Algae cultures contained higher percentages of n-3 PUFA during the logarithmic phase than in the stationary phase when the proportions of short-chain fatty acids increased. High levels of concentrated CO sub(2) generally increased the content of long chain fatty acids from 17 carbon atoms onwards. The percentages of total n-3 and n-6 were higher than those recorded at low CO sub(2) concentration. Similarly, the n- 3/n-6 ratio was higher at the maximum CO sub(2) concentration (logarithmic phase). During stationary phase the difference between the two groups was less apparent than that observed in the logarithmic one. The high CO sub(2) addition exerted a significant and more favorable influence than the low supplementation on the C18:1, C20:0, C20:4n-6, and C22:6n-3 concentrations in both phases, in all four microalgae strains studied.

Commercial mud crab (Scylla spp.) aquaculture in many countries has been stifled to some degree by a lack of seed stock. A commercially viable larval rearing protocol for Scylla serrata has yet to be established. Two experiments were conducted to assess the requirement for rotifers in the larval feeding regime for S. serrata. These examined the timing of introduction and cessation of rotifers, and co-feeding protocols with Artemia. In the first experiment, it was shown that rotifers were necessary in the feeding regime for acceptable growth and survival, and when used as the only food source during the first zoeal stage (Z1), gave better survival than when co-fed with Artemia. It was also found that when rotifers were removed from the co-feeding regime at Z3, no detrimental effect on growth or survival occurred. Final survival to megalop of 58.67 plus or minus 7.35% was achieved when rotifers were fed singly up to zoea 2 and then co-fed with Artemia through to megalop. Crab larvae fed only Artemia throughout the rearing period took significantly longer to reach the megalop stage and suffered higher levels of mortality. The second experiment investigated the effects on survival, when rotifer feeding was discontinued at Z2, Z3, Z4, Z5 and when rotifers were fed up to the megalop stage (M). Artemia were offered to these treatments from Z2 onwards. A no-rotifer (NR) control that was fed Artemia-only from stocking, was also tested. It was again shown that rotifers, especially in the early stages, promoted acceptable levels of survival and growth. Without rotifers, moulting of crab larvae was delayed and survival was significantly lower during the first two zoeal stages. There was also a significant difference in survival to megalop, and a significant negative relationship between duration of rotifer feeding and survival to megalop. The best survival of 78.00 plus or minus 5.54% was achieved when rotifers were removed from the feeding regime at Z2. The NR treatment had the lowest survival of 32.00 plus or minus 7.51%. These trials established that while rotifers are a valuable inclusion in the feeding regime for larval S. serrata, their use should be limited to the first zoeal stage only to maximise growth and survival.

This comparative survey summarizes six individual studies on the ecological effects of two common perfluorinated surfactants, PFOS and PFOA, on zooplankton. We compare the test designs and quantify the relative sensitivity and statistical power (1-beta > or = 0.8). The survey compares 30-L indoor microcosm to 12,000-L outdoor microcosm experiments, with 225-mL single species laboratory tests as reference. By this we elucidate the extrapolation of ecological effects in space and complexity. Generally, zooplankton had lower tolerance toward PFOS than toward PFOA. With increasing concentrations the zooplankton community became simplified toward more robust rotifer species, which, as an indirect effect, increased their abundance due to a shift in competition and predation. The statistical power of the designs exhibits inverse proportionality between complexity and realism, indoor microcosm>outdoor microcosm. Surprisingly, the 30-L study had a lower LOEC value for Daphnia magna than the laboratory chronic test, indicating that D. magna and D. pulicaria were not the most sensitive species and that laboratory tests are not always conservative relative to microcosm experiments. Food scarcity due to phytotoxicity was not the reason for the difference.

We tested the reciprocal effects of water conditioned by exudates of Aeolosoma sp. (Aphanoneura, Oligochaeta) and fish (Skiffa lermae: Goodeidae) and by the presence of Aeolosoma sp. on the population dynamics of four species of anomopod cladocerans (C. cornuta, C. dubia, S. serrulatus and S. vetulus) at 25 degreesC for 26 days using Chlorella vulgaris (1 x 10(6) cells ml(-1)) as a basic food for all. We found that, regardless of treatment, C. cornuta and C. dubia had a long initial phase of slow growth, followed by a rapid increase after the second week and that, regardless of treatment, C. dubia had a higher rate of population increase per day than C. cornuta. S. vetulus had a longer lag phase than S. serrulatus. Fish-conditioned water resulted in growth inhibition in S. serrulatus, but had no effect on S. vetulus, while Aeolosoma-conditioned water inhibited growth of S. vetulus but not that of S. serrulatus. Our results suggest a scale of responses of cladocerans to exposure to fish- and worm-conditioned water and to the presence of worms, ranging from a mild stimulation to no effects to inhibited growth. Kairomone-effects on body size of C. cornuta were not significant, but beak length was strongly influenced, and more by fish than by worm kairomones. In S. vetulus, differences in size were not significant. However, individuals grown in the presence of worms had higher biomass while those grown in the presence of fish and worm kairomones showed a decreased weight. Effects of worm exudates and of their live biomass on cladocerans were thus opposite in Simocephalus. In Ceriodaphnia dubia, in contrast, they were additive. Aeolosoma was depressed by all four cladocerans, although worms tried to penetrate the valves of the cladocerans to feed on the tissue inside. In doing so, they suffered significant casualties, especially from blows of the powerful post-abdomen of Simocephalus. The nature of the cladoceran-worm interaction is therefore far from simple: in addition to the 'chemical communication' that is present, it has a predatory component (worms trying to feed on cladocerans) but the reverse might also be true (cladocerans filtering out tissues of disrupted Aeolosoma). Since both worms and cladocerans feed on algae, exploitative competition also seems to be involved. In this, the worms appear to be the inferior partner, although none of the experiments lasted long enough to drive any of the competing partners to extinction.

The limnology of Lago Biao and Lago Loreto, two tropical crater lakes on the island of Bioko, was investigated for the first time in January of 2002. Lago Biao fills a caldera at 1750 m altitude and is 18.5 m deep. This lake was characterized by low conductivity (11.6-13.3 mu S cm super(-1)), low pH (5.9-6.2), an oxycline between 6 and 10 m depth (90-27% saturation), and a Secchi depth of 5.5 m. Dinoflagellates, desmids, and green algae dominated the phytoplankton community. The rotifers Anuraeopsis fissa, Polyarthra indica, Trichocerca simoneae, and T. similis were most abundant above or in the thermocline. During the day Tropocyclops prasinus tjeefi and Chaoborus cf. ceratopogones concentrated in the oxycline, whereas Daphnia laevis was most abundant between 0 and 4 m depth. In contrast, L. Loreto is 82 m deep and probably fills an explosion crater ('maar') at 1050 m altitude. The lake had a turbid, yellowish appearance and a Secchi depth of only 0.6 m. Oxygen content dropped from 121% at the surface to 6% in 10 m depth. The pH declined from 9.15 at the surface to 7.4 in only 2.5 m depth and became acidic at approximately 15 m depth. One species of cyanobacterium, one dinoflagellate and one green alga dominated the phytoplankton and together reached densities of 12 100 cells ml super(-1). Only one rotifer (Brachionus angularis) and one copepod (Tropocyclops prasinus tjeefi) species colonized the open water. Intact algal cells and zooplankton specimens were encountered near the bottom.

In monogonont rotifers parthenogenetic reproduction allows population growth, and mictic (sexual) reproduction leads to the production of diapausing eggs. When amictic females are exposed to a mixis stimulus, they produce mictic daughters, whose eggs develop into males or, if fertilized, into diapausing eggs. Experiments showed that mictic offspring production is initiated by crowding in females of Brachionus angularis Gosse 1851, Epiphanes senta (O.F. Mueller 1773) and Rhinoglena frontalis Ehrenberg 1853, just as it is in Brachionus calyciflorus Pallas 1766 and B. plicatilis Mueller 1786. In B. calyciflorus, B. angularis, E. senta and R. frontalis, the propensity of amictic females to respond to crowding by producing mictic female offspring is low in the stem female hatching from a diapausing egg, but then increases after some generations. In many cases, only few mictic offspring are produced by crowded females of the second to the fifth generation, but the maximal response occurs only in later generations. Delayed sexual reproduction in early generations from the resting egg may be advantageous, because it first favours rapid population growth and later on maximizes resting egg production. However, it may be disadvantageous, if unpredictable environmental variation causes a population decline when sexual reproduction is still suppressed. The extent to which sexual reproduction is delayed varies among and within species. When strains from populations in temporary and permanent habitats were compared, sexual reproduction was significantly delayed in strains from temporary habitats in all species, whereas in B. calyciflorus and R. frontalis mixis was not significantly delayed in strains from permanent habitats. In E. senta mixis was significantly delayed in clones from both habitat types. Within all strains there was significant variation among clones in the propensity to produce mictic offspring, the extent to which sexual reproduction was delayed in the first generations after the stem female hatched, or both.

We report on the gamma -diversity of Rotifera in freshwater habitats of the River Mun floodplain, Northeast Thailand. Qualitative samples were collected during the pre-monsoon (April) and post-monsoon (October) periods of 2000, from 70 habitats spanning a diverse array of freshwater habitat types. Of the 184 species identified, most belong to Lecane (31.0%), followed by Trichocerca (12.0%), Lepadella (11.4%) and Brachionus (8.2%). Oriental, Australasian, and Eastern hemisphere taxa account for 4.3%, 3.3% and 7.1%, respectively, of the total rotifer fauna, and 8.8%, 1.7% and 10.5%, respectively, of Lecane. Although comparison between studies is difficult, these numbers conform to previous reports on the diversity and composition of the rotifer fauna of Thai freshwater habitats, and of tropical floodplain ecosystems. Diversity is lowest during the post-monsoon period, which may result from disturbance by monsoon conditions. Two morphospecies, Brachionus srisumonae n. sp., and Lecane niwati n. sp., are described as new to science. Additional noteworthy occurrences are, Lecane robertsonae Segers, previously considered a Neotropical endemic, and L. subtilis Harring & Myers, a tropicopolitan species new to Thailand and the Oriental region.

Zooplankton communities of Umiam reservoir, Meghalaya studied (during November, 1996- October, 1998) at 4 sampling stations (I-IV) indicated 16-35 species, wider community similarity (0-86.5%) and comprised 29.2-41.7% of net plankton abundance. Rotifera depicted qualitative and quantitative dominance, Cladocera and Copepoda are subdominant groups while Rhizopoda, Ostracoda and Nematoda showed poor densities. ANOVA registered significant variations in zooplankton abundance between months and sampling stations; Rotifiera and Cladocera showed significant density differences between months. Zooplankton indicated moderate species diversity, high evenness and low dominance; diversity and dominance recorded significant variations between stations. Multiple regression exhibited higher cumulative influence of 16 abiotic factors (84.0-87.0%) on temporal variations of zooplankton. Q(B/T) quotient affirmed "mesotrophic" nature of Umiam reservoir.

The burbot (Lota lota) is the only fresh water member of the cod family, Gadidae, and is adapted to cold waters. The effects of temperature and light on the growth and survival of burbot larvae were investigated under hatchery conditions. Three temperature regimes (12, 16 and 20 degree C) were applied under continuous light and darkness during the experiment. Rotifer, Brachionus calyciflorus (L.) were fed to the larvae in the first 10 days and the diet was then replaced with Artemia nauplii. At the end of the feeding stage with rotifer, growth in terms of the total length and wet weight were larger at higher temperatures under continuous light. At day 10, survival rates of the fish held at 12 degree C under continuous light and darkness regime were higher than those held at 16 degree C and 20 degree C kept under the same conditions. From day 10 onwards, larval growth improved remarkably after changing the live food from rotifer to Artemia in all treatments. At the end of the study, the highest survival rate was recorded among the larvae held at 12 degree C exposed to continuous light. Under light condition, the temperature of 20 degree C did not result in an improved larval growth compared with 16 degree C. This may indicate that high temperature and continuous light are not beneficial for larval growth and survival when they reach older stage of development. The results indicate a significant interaction for the combination of temperature, light and time with respect to survival and wet weight, making unambiguous interpretation of the main effects difficult.

Nematodes, rotifers and tardigrades were collected on three nunataks (mountain peaks penetrating the ice sheet) in Vestfjella, on six nunataks in Heimefrontfjella and on the Schirmacher Oasis in East Antarctica in the austral summers of 1996/97 and 2001/02. Most samples were taken on the nunatak Basen in Vestfjella where the Swedish station Wasa is located. The microfauna was patchily distributed and the highest densities of animals were found on sites with visible vegetation of mosses, lichens or algae. Thirty-four taxa of nematodes and tardigrades were found. Only seven of these occurred regularly in apparently actively reproducing populations. Other occasional records of nematodes had very few specimens. The highest number of species was found on the nunatak Basen. Rotifers, found in 66% of the samples, were the most frequent animal group. Nematodes occurred in 37% of the samples and tardigrades in 42%. The most frequent nematodes were Plectus and Panagrolaimus, occurring in 26% and 5% of the samples, respectively. Macrobiotus, Hebesuncus and Acutuncus were the most frequent and abundant tardigrades. The pattern of animal distribution can be related to both habitat characteristics and to the geographic position of the nunatak. The communities are little organised and the distribution of the fauna has similarities with an early phase of colonisation.

Influence of inorganic N sub(2) forms on pond food organisms was investigated. Seven identified plankton taxa comprising four phytoplankton; Desmidiaceae (desmids), Bacillariophyceae (diatoms), Cyanophyceae (blue-green algae) and Chlorophyceae (green algae) and three zooplankton; Protozoa, Cladocera and Rotifera fluctuated in response to nutrient inputs. All recorded significant F-value across treatments. With exception of blue-green algae, other phytoplankton groups had comparable relatives abundances in treatment with higher concentration of readily utilized. Nitrate-Nitrogen (NO sub(3) super(-)N) compared with control that recorded higher concentration of Ammonia-Nitrogen (NH sub(3) super(-)N) and increased relative abundance of blue-green algae. Zooplankton exhibited same dominance pattern of Protozoa, Rotifera and Cladocera respectively, with treatment recording higher abundance in response to edible phytoplankton. N sub(2) from zooplankton excretion influenced phytoplankton responses in the control. Ammonia-Nitrogen (NH sub(3) super(-)N), Nitrate-Nitrogen (NO sub(3) super(-)N) and Nitrite-Nitrogen (NO sub(2) super(-)N) were observed to fluctuate along nutrient enrichment profile depending mostly on the concentrations of intermediate Nitrite-Nitrogen (NO sub(2) super(-)N). All nutrient parameters except NH sub(3) super(-)N recorded significant t and F statistic and across treatments. Water quality parameter of pH and dissolved oxygen were favourable for most period of the experiment.

The impacts of global warming on aquatic ecosystems are expected to be most pronounced at higher trophic levels in cold-water environments. Therefore, we hypothesized that warming of fishless alpine ponds would suppress large-bodied consumers (e.g., cladocerans, copepods) and stimulate fast-growing microorganisms (e.g., phytoflagellates, rotifers), thereby altering the community composition and total abundance of zooplankton and phytoplankton. This hypothesis was tested using three blocks of four experimental mesocosms (1000-liter capacity) that were located next to alpine ponds in Banff National Park, Canada. Each block received unfiltered pond water and sediment from a pond following ice out in June 2000. A warming treatment (control vs. 3.6 degree C warmed) was achieved by controlling the ventilation of greenhouse canopies that were suspended over each of the mesocosms. By the end of our 50-d experiment, warming significantly suppressed total zooplankton biomass because large cladocerans (Daphnia pulex) declined while rotifer (Keratella cochlearis, Conochilus unicornis) abundance increased during the second half of the experiment. In contrast, warming did not affect total phytoplankton biomass but significantly altered community composition by favoring phytoflagellates (Mallomonas, Synura, Trachelomonas) over larger filamentous green algae (Mougeotia, Phymatodocis). Warming did not significantly increase dissolved nitrogen and phosphorus concentrations. Therefore, warmer growing conditions and reduced grazer biomass best explained the increased abundance of more edible, fast-growing phytoflagellates in the warmed mesocosms. Our findings support the hypothesis that moderate warming can destabilize plankton dynamics, thereby potentially reducing the reliability of water quality and food resources for higher trophic levels (e.g., planktivorous fish) in shallow cold-water ecosystems.

Four laboratories were compared to ascertain the reproducibility of test methods for five bioassays: the ten day whole sediment bioassay with the amphipod Corophium volutator, the fourteen day whole sediment bioassay with adult sea urchins Echinocardium cordatum, the Microtox solid phase bioassay with the bacterium Vibrio fischeri, the oyster larvae sediment elutriate bioassay using Crassostrea gigas and the sediment pore water bioassay with the rotifer Brachionus plicatilis. The bioassays were all conducted according to the standard operating procedures of the National Institute for Coastal and Marine Management/RIKZ and carried out with one control sediment and three moderately contaminated dredged materials from the Netherlands. Reference toxicant tests were also performed for every bioassay, to assess the condition of the test species. Reproducibility and inter-laboratory variability were evaluated by calculating coefficients of variation for the sediment bioassays and considering the ability of each laboratory to achieve the test acceptability criteria and to identify a number of confounding factors. The bioassays involving the amphipods and sea urchins had an acceptable inter-laboratory variability, with average coefficients of variation of 20% or less. The Microtox solid phase bioassay showed high reproducibility and the least variability among laboratories, with average coefficients of variation of 12%. In contrast, the results for percent net response in the oyster larvae bioassay were very variable and poorly reproducible: in three of the four sediments the coefficients of variation exceeded 100%. Two laboratories did not meet the test acceptability criterion for oyster embryo development in the control sediment. Survival in the rotifer bioassay also varied greatly among laboratories with average coefficients of variation of 48%. We conclude that the main sources of inter-laboratory variability were 1) individual differences in the skill and experience of laboratory technicians (for the amphipod, oyster larvae and rotifer bioassays); 2) the use of different batches of test organisms (sea urchin bioassay) and 3) the use of different dilution water (oyster larvae bioassay).

This study was conducted to examine the effect of essential fatty acids (EFA) on the survival, development and bioconversion of fatty acids in mud crab Scylla serrata larvae. Mud crab larvae held in 1-l plastic beakers (30 ind/l) were fed rotifers that had been enriched with oleic acid (18:1n-9, OA), linoleic acid (18:2n-6, LA), linolenic acid (18:3n-3, LNA), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) ethyl ester oil during the zoea (Z)1 and Z2 stage. Upon reaching the Z3 stage, rotifers were shifted to unenriched Artemia or Artemia enriched with either EPA or DHA ethyl ester. Further in order to allow comparison of the effect of the enriched rotifers on the fatty acid composition of the Z2 stage larvae, larvae fed enriched rotifers were harvested upon reaching the Z2 stage for fatty acid analysis. The survival of mud crab larvae was more strongly affected by the EFA contained in the Artemia compared to rotifers. Mud crab larvae fed unenriched Artemia showed EFA deficiency signs such as lower survival, longer intermolt period, and a narrower carapace width at the first crab stage, indicating that DHA was superior to that of EPA and followed by LNA and LA. The fatty acid composition of the whole body of Z2 larvae fed rotifers enriched with OA, LA or LNA revealed that the content (g/100 g larvae) of EPA decreased from 1.2 to 0.4-0.8 and DHA decreased from 0.5 to 0.1-0.2, respectively. Moreover, the contents of monoenes increased from 1.4 to 2.5-3.2, indicating dietary EFA deficiency. We conclude that mud crab larvae have a limited or negligible capability to convert C18 unsaturated fatty acids to highly unsaturated fatty acids.

The coupling between bacteria and heterotrophic nanoflagellates (HNF) was examined in nine lakes of low productivity for evidence of the effects of various metazooplankton (i.e. rotifers, cladocerans and copepods) on this relationship. We considered the size of cladocerans and, in contrast to most previous across-system studies, the three strata of the water column (i.e. epilimnion, metalimnion and hypolimnion). Rotifers were numerically dominant in all lakes and accounted for 45-84% of total metazooplankton abundance, while the abundance of large cladocerans was relatively low, ranging from 0.066 to 15.2 ind. L super(-1). The across-lake relationship between bacteria and HNF was significant in the deeper strata (meta- and hypolimnion) but not in the epilimnion and in the two groups of lakes separated on the basis of their average number of large cladocerans (<5 and >5 ind. L super(-1), respectively). The results confirmed the negative impacts of large cladocerans on HNF, but also showed that rotifers, probably through grazing on HNF, may be an important factor causing variation in the bacteria-HNF relationship in unproductive waters. Quadratic models best described the relationships between metazooplankton and the ratio of bacteria to HNF. This ratio seemed to be a result of complex interactions between several factors, including the zooplankton composition and abundance and the depth of the lake. Indeed, this ratio significantly decreased across lakes, with increase in depth. In addition, shallower lakes (having <5 large cladocerans L super(-1) and fewer Polyarthra vulgaris) tended to have more bacteria and HNF and a higher ratio of bacteria to HNF than deeper lakes (which had >5 large cladocerans L super(-1) and substantial proportions of P. vulgaris). We suggest that the epilimnion, metalimnion and hypolimnion of lakes be taken into account when analysing the bacteria-HNF relationship as well as the cascading effects of zooplankton on microbial communities.

Fat snook (Centropomus parallelus) is a candidate species for aquaculture, but little work has been done towards commercialization of this species. A major constraint has been the inability to obtain consistent and predictable larval survival to metamorphosis, a consequence of high mortality during the first-feeding stage. Attempts have been made to increase survival by increasing prey density to levels (30-40 prey/ml) exceeding those used for rearing most marine species (5-20 prey/ml). Our objective was to investigate the effects of lowering prey densities during larval rearing on the foraging behaviour, growth and survival of fat snook. Larvae were raised from hatch to 7the commencement of metamorphosis (16 days) at four prey densities: 5, 10, 20 and 30 rotifers/ml. Survival was high in all treatments, but highest (38.8%) at 5 prey/ml. Fat snook larvae were found to be visually guided predators that forage with a saltatory search pattern. In the presence of prey, fat snook larvae spent the majority of their time in the pause or non-swimming state punctuated by occasional swimming bursts usually directed towards a prey item. The range of prey densities tested did not significantly affect growth rates or survival, and there were no differences in foraging behaviours between treatments. Therefore, we recommend production scale trials at these lower rotifer densities for larval fat snook as the results of this work imply that reducing prey densities to 5 rotifers/ml during the larval period would not affect juvenile production and would be more cost effective.

The feeding is one of the most important factors to larval development and the sucess of the commercial cultivation of decapod crustacean larvae depends on the efficient and economic utilization of the available food. The performance of Macrobrachium rosenbergii larva submitted to four different feeding systems was tested by using the daily observation of the larval substages and the first metamorphoses. The larvae were stocked in a density of approximately 100 larvas.l(-1), in 16 tanks, with 33 liters capacity. The experiment was divided in four experimental units (blocks). Four feeding systems were tested in the hatchering in an open circuit, with four replicates for treatment. The feeding systems in which progressive substitutions of the nauplii of Artemia sp. (nas) were accomplished, for the rotifer Brachionus plicatilis (rots), the following treatments were tested: 100% Brachionus plicatilis(30 rots/mL) (T1); 100% Artemia(5 nas/mL) (T2), 60% Artemia(3 nas/mL)+ 40% Brachionus plicatilis (12 rots/mL) (T3) and 40% Artemia (2 nas/mL) + 60% Brachionus plicatilis (18 rots/mL) (T4), Humid ration was added to all treatments. The results of the change of the larval stage demonstrated that there was not significant difference among the treatments T2, T3 and T4. The treatment T1 (100% Brachionus plicatilis) had total mortality in the 14(th) day of the experiment. The effect of the occurrence of the first metamorphoses for post-larvae, ocurred at 27(th) day in the treatments T2, T3 and T4. Consequently, the hatchering cycle to the metamorphosis of 90% for post-larvae (PL1), was the same in the respective treatments (35 days). Therefore, the use of the enriched rotifer and frozen in the feeding systems of the larvae allowed a satisfactory performance in terms of larval development of M. rosenbergii until the passage for the post-larvae stage.

This work was carried out to identify the replacement of the nauplii Artemia sp. for the enriched and frozen rotifer (Brachionus plicatilis O.F. Muller, 1786) on the larval development and survival of the freshwater prawn M. rosenbergii. The experiment was developed according to the following treatments: 100% B. plicatilis (3 0 rots/ mL) (T1); 100% Artemia sp. (5 nas/ mL) (T2), 60% Artemia sp. (3 nas/ mL) + 40% B. plicatilis (12 rots/ mL) (T3) e 40% Artemia sp. (2 nas/ mL) + 60% B. plicatilis (18 rots/ mL) (T4). Humid ration was added to all treatments. The results of the final survival in post-larvae were analyzed by the X-2 test and demonstrated no significant differences from treatment T2 (68.36%) to T3 and T4: 68.76% and 64.60%, respectively. T1 treatment (100% B. plicatilis) presented total mortality at 14(th) day of the experiment. Average dry weight of the pos-larvae was analyzed statistically by ANOVA and showed no significant differences in values: 3.29 mg (T2), 3.08 mg (T3) and 3.38 mg (T4). No significant differences among treatments T2, T3 and T4 were observed. The best mortality rate was observed from 1 to 15 day of hatchery based on the number of dead larval stored in the daily material siphoned. Therefore, these results suggest that the total substitution of the enriched and frozen rotifer is not recommended due to a total mortality of larvae, whereas the partial replacement of 40% and 60% of the Artemia sp nauplii by the enriched and frozen rotifer is possible, with no significant damages to survival and post-larval growth.

This study assessed the dietary value of rotifers at different culture stages for larvae of red seabream (Pagrus major). Cultures were prepared daily and cultured for up to eight days. Rotifers were taken out of the batch culture and equally enriched with freshwater Chlorella containing docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The fish larvae were reared in 500-L tanks for 20 days and supplied with enriched rotifers at the 2nd, 4th, 6th, or 8th day of batch culture. Mortality of enriched rotifers was the highest on the 8th day, and their egg production rate, which is a prime index of their physiological status, became low. The larvae fed on those rotifers showed the lowest growth at the 20th day after hatching. Despite the almost equal DHA and EPA levels in rotifers of all groups, the EPA level in fish was the lowest on the 8th day of batch culture. These results show that the dietary value of rotifers was poor during or just before the stationary growth phase of batch culture, in spite of enrichment with DHA and EPA.

Cryopreservation, a technique of high potential for culture collections, might offer a solution for reliable supply of microalgae in aquaculture units. Marine microalgae used in aquaculture were cryopreserved under 4, -20 and -80 degree C using common cryoprotectants (methanol, dimethylsulfoxide (DMSO), propylene glycol and polyvinylpyrrolidone (PVP)) with promising results for Chlorella minutissima, Chlorella stigmatophora, Isochrysis galbana and Dunaliella tertiolecta. As cryoprotectants usually are toxic above certain concentrations and exposure time, and assuming that low amounts of cryoprotectants will remain in regenerated cultures, an experimental scheme was employed to explore the lower limits of safety for these algae and their primary consumers in hatchery food chains. Results showed that methanol was well tolerated by C. stigmatophora and D. tertiolecta up to a concentration of 1.6% (v/v) while I. galbana could not survive in culture at any concentration and C. minutissima exhibited some 30% of the control's yield at 0.2%. DMSO was highly tolerated up to 1.0% by all strains with the Chlorella strains surviving well up to 2%. Propylene glycol was not only tolerated up to 8% by Dunaliella but induced mixotrophic growth as well, while for Isochrysis it was lethal at any concentration. Among zooplanktonic consumers, brine shrimp Artemia nauplii could tolerate very high concentrations of the tested cryoprotectants, the rotifer Brachionus plicatilis was found sensitive to low amounts of PVP, while the nauplii of the shrimp Penaeus japonicus and the crab Eriocheir sinensis were in general very sensitive to all cryoprotectants and in several cases to much lower amounts than 1%. However, as long as the residues of cryoprotectants are kept below 1% in the regenerated cultures, there will be no problem with the animal consumers.

We studied the occurrence of colony formation within 40 different strains of Scenedesmaceae (Chlorococcales, Chlorophyta) in response to grazing-released infochemicals from the herbivorous zooplankters Brachionus calyciflorus Pallas (Rotifera) and Daphnia magna Strauss (Cladocera). With the exception of two strains, all strains showed similar responses to both B. calyciflorus and D. magna infochemicals, either no response or inducible colony formation. Colony size was found to increase with B. calyciflorus infochemical concentration and could be described by a sigmoid function. The increase in colony size was more pronounced in the Scenedesmus species tested than in Desmodesmus species, which was probably due to higher threshold infochemical concentrations for colony induction in Desmodesmus. Therefore, the adaptivity of colony formation to the herbivory threat only holds above the threshold concentration for colony induction and as long as maximum colony size has not been attained. Taking this into account, our results suggest that inducible colony formation is a common adaptive response of many Scenedesmaceae to the threat of herbivory.

Recent theoretical work (Vos et al. 2004) predicts that inducible defences prevent strong population fluctuations under high levels of nutrient enrichment. Here we evaluate this model prediction and show that inducible defences in algae stabilize the dynamics of experimentally assembled bi- and tritrophic planktonic food chains. At high phosphorus levels, we observed strong population fluctuations in all food chains with undefended algae. These fluctuations did not occur when algae had inducible defences. At low phosphorus levels, we observed deterministic consumer extinctions, as predicted by stoichiometric theory. Our study thus shows that both biotically and abiotically induced changes in algal food quality affect the stability and persistence of planktonic food chains.

Herbivore populations are commonly restricted by resource limitation, by predation or a combination of the two. Food supplement experiments are suitable for investigating the extent of food limitation at any given time. The main part of this study was performed in an extremely acidic lake (pH 2.7) where the food web consists of only a few components and potential food sources for herbivores are restricted to two flagellates. Life table experiments proved that Chlamydomonas was a suitable food source whereas Ochromonas was an unsuitable food source. The two flagellates and the two rotifers exhibit a pronounced vertical distribution pattern. In this study, a series of food supplement experiments were performed in order to: (1) quantify and compare potential resource limitation of two primary consumers (Cephalodella hoodiand Elosa worallii, Rotatoria) over time, (2) compare their response at different temperatures, (3) evaluate the effect of having an unsuitable food source alongside a valuable one, (4) estimate the effect of predation on rotifers by Heliozoa, and (5) compare the results with those from other acidic lakes. Additionally, the spatio-temporal population dynamics of both species were observed. The field data confirmed a vertical separation of the two species with E. worallii dominating in the upper water layers, and C. hoodi in the deeper, cooler water layers. The results from the food supplement experiments in which Chlamydomonas served as the supplemented suitable food source showed that the two rotifers were food limited in the epilimnion throughout the season to different extents, with Cephalodella being more severely food limited than Elosa. The experiments at different temperatures provided evidence that Elosa had a higher optimum temperature for growth than Cephalodella. When the unsuitable food algae Ochromonas was added alongside the suitable food source Chlamydomonas, C. hoodi was unaffected but E. worallii was negatively affected. Predation of Heliozoa on rotifers was observed but the total effect on the rotifer dynamics is probably low. The comparison with other lakes showed that resource limitation also occurred in one other lake, although to a lesser extent. Overall, the vertical separation of the two rotifers could be explained by both their differential extent of resource limitation and differential response to temperature.

A field study was conducted in Santala Bay with weekly samplings during February and March 2000. Ice thickness was 20-28 cm, snow cover 0-1 cm. The under-ice water column was stratified with a cold (-0.3-0.2 degree C) and less saline (S = 2.1-4.9) interface layer. Concentrations of particulate organic carbon (0.5-5.8 mg POC l super(-1)) and algal pigments (0.3-18.2 mu g chlorophyll a l super(-1)) were higher in the ice than in the water (0.2-0.5 mg POC l super(-1), 1.6-7.1 mu g chlorophyll a l super(-1)) and peaked mostly in the bottom part of the ice. The thin ice and almost lacking snow cover had favoured an early ice-algal and phytoplankton bloom. The diversity of metazoans was low, with six species in the ice and eight species in the under-ice water. The rotifer Synchaeta cf. littoralis dominated both in ice and water, with maximum abundances of 230 individuals l super(-1) in the bottom part of the ice. Rotifer eggs were also observed in the ice. Baltic sea ice seems to be a suitable habitat for rotifers. Nauplii and copepodids of the calanoid Acartia longiremis in the under-ice water showed some herbivorous feeding (<0.1-0.23 ng gut pigment individual super(-1)), but analysis of fatty acids, fatty alcohols and biomarker ratios indicated a more omnivorous/carnivorous diet. Despite low temperatures, this copepod showed growth and development below the ice, doubling in numbers (mainly CI, CII) from 118 to 230 individuals m super(-3) during the third week of March.

A field study was conducted in Santala Bay with weekly samplings during February and March 2000. Ice thickness was 20-28 cm, snow cover 0-1 cm. The under-ice water column was stratified with a cold (-0.3-0.2degreesC) and less saline (S=2.1-4.9) interface layer. Concentrations of particulate organic carbon (0.5-5.8 mg POC l(-1)) and algal pigments (0.3-18.2 mug chlorophyll a l(-1)) were higher in the ice than in the water (0.2-0.5 mg POC l(-1), 1.6-7.1 mug chlorophyll a l(-1)) and peaked mostly in the bottom part of the ice. The thin ice and almost lacking snow cover had favoured an early ice-algal and phytoplankton bloom. The diversity of metazoans was low, with six species in the ice and eight species in the under-ice water. The rotifer Synchaeta cf. littoralis dominated both in ice and water, with maximum abundances of 230 individuals l(-1) in the bottom part of the ice. Rotifer eggs were also observed in the ice. Baltic sea ice seems to be a suitable habitat for rotifers. Nauplii and copepodids of the calanoid Acartia bifilosa in the under-ice water showed some herbivorous feeding (<0.1-0.23 μg gut pigment individual(-1)), but analysis of fatty acids, fatty alcohols and biomarker ratios indicated a more omnivorous/carnivorous diet. Despite low temperatures, this copepod showed growth and development below the ice, doubling in numbers (mainly CI, CII) from 118 to 230 individuals m(-3) during the third week of March.

Seasonal variations in plankton community response to pentachlorophenol (PCP) were studied in four mesocosm experiments using enclosures in a small lake. The mesocosms (860 l) were dosed with single applications of technical grade PCP (0, 4, 10, 24, 36, 54, 81 and 121 microg/l PCP) and monitored for 20 days. Multivariate statistical analyses showed that plankton community taxonomic composition varied with season. In winter and spring, communities were most stable in time; species diversity and abundance were lowest in winter. Seasonally, the communities varied little with respect to the dominant species, which were the copepod Calamoecia lucasi, the alga Peridinium sp. and the rotifer Ascomorpha ovalis. The direct effects of the PCP additions varied little between seasons, but indirect effects were evident at lower treatment levels in autumn. Indirect effects were not evident in winter. Minor variations in plankton community responses to PCP with season were apparent in the following order of decreasing sensitivity; autumn > or = winter/spring > or = summer. At the species level, C. lucasi showed the largest response. The responses observed were greatest in autumn, with decreased abundance at PCP concentrations > or = 24 microg/l. In the other seasons, effects were observed at levels of 54 or 81 microg/l and higher. Ascomorpha ovalis was the most responding rotifer in winter and spring, whereas Anuraeopsis fissa responded more strongly in autumn and summer. The dinoflagellate alga Peridinium sp. had the largest negative response in all but winter, when Dinobryon cylindricum did. Cryptomonas sp. responded positively to PCP in all seasons, increasing in abundance in the highest treatments, possibly due to reduced grazing pressure, reduced competition, or increased decomposition. The plankton community no-observed effect-concentration (NOEC) was 24-36 microg/l PCP. Results reported here suggest that the Australian and New Zealand water quality guideline values for PCP are sufficient to protect plankton communities against adverse effects.

Populations living in seasonal environments are exposed to systematic changes in physical conditions that restrict the growth and reproduction of many species to only a short time window of the annual cycle. Several studies have shown that climate changes over the latter part of the 20th century affected the phenology and population dynamics of single species. However, the key limitation to forecasting the effects of changing climate on ecosystems lies in understanding how it will affect interactions among species. We investigated the effects of climatic and biotic drivers on physical and biological lake processes, using a historical dataset of 40 years from Lake Washington, USA, and dynamic time-series models to explain changes in the phenological patterns among physical and biological components of pelagic ecosystems. Long-term climate warming and variability because of large-scale climatic patterns like Pacific decadal oscillation (PDO) and El Nino-southern oscillation (ENSO) extended the duration of the stratification period by 25 days over the last 40 years. This change was due mainly to earlier spring stratification (16 days) and less to later stratification termination in fall (9 days). The phytoplankton spring bloom advanced roughly in parallel to stratification onset and in 2002 it occurred about 19 days earlier than it did in 1962, indicating the tight connection of spring phytoplankton growth to turbulent conditions. In contrast, the timing of the clear-water phase showed high variability and was mainly driven by biotic factors. Among the zooplankton species, the timing of spring peaks in the rotifer Keratella advanced strongly, whereas Leptodiaptomus and Daphnia showed slight or no changes. These changes have generated a growing time lag between the spring phytoplankton peak and zooplankton peak, which can be especially critical for the cladoceran Daphnia. Water temperature, PDO, and food availability affected the timing of the spring peak in zooplankton. Overall, the impact of PDO on the phenological processes were stronger compared with ENSO. Our results highlight that climate affects physical and biological processes differently, which can interrupt energy flow among trophic levels, making ecosystem responses to climate change difficult to forecast.

The effect of temperature on the life history characteristics of amictic females (AF), unfertilized mictic females (UMF) and fertilized mictic females (FMF) in Brachionus calyciflorus was studied with replicated individual cultures at 20 degree C, 25 degree C and 30 degree C, and with algae Scenedesmus obliquus for their food. There were highly significant effects of both temperature and female type, independently and interactively, on the duration of juvenile and post-reproduction periods, and the number of eggs produced by the rotifer per life cycle. Among all the temperature-female type combinations, all the juvenile periods of FMF, and the post-reproduction periods of UMF and FMF at 20 degree C, were the longest, and the number of eggs produced by an UMF at 30 degree C was the highest. There were highly significant effects of both temperature and female type on the duration of the reproduction period, but no clear correlation was observed between temperature and female type. The reproduction period of AF was longer than that of UMF and FMF. Only temperature influenced significantly the mean life-span of the three types of females. The duration of juvenile, reproduction and post-reproduction periods as well as the life-span of the three types of females were all reduced very significantly with rise of temperature, but the rates of reduction varied with female type. Among the three types of females, the number of eggs produced per life cycle by an UMF was the highest, and that of a FMF was the lowest. A significant relationship between the number of eggs produced per life cycle and temperature was observed only in the UMF.

Laboratory populations of three strains of Brachionus calyciflorus Pallas (Qingdao, Wuhu, and Guangzhou strains) collected respectively from River Huanghe, River Changjiang and River Zhujiang basins of China were cultured at 20 degree C, 25 degree C, and 30 degree C with 3.0x10 super(6) cells/ml of Scenedesmus obliquus to investigate their resting egg productions. There were significant effects of both temperature and strain, independently and in interaction on resting egg production. The resting egg productions of the rotifers at 20 degree C and 25 degree C were not significantly different, but were lower than those at 30 degree C. Resting egg productions of the Qingdao and Wuhu strains were not significantly different, but were higher than that of the Guangzhou strain. The total production of fertilized mictic females depended on the production of total females and the mixis and fertilization rates. Among all the strain-temperature combinations, the resting egg productions of the Wuhu and Qingdao strains at 30 degree C were the highest (1202.33 plus or minus 102.50 and 1258.67 plus or minus 403.45 ind./10ml/12d, respectively).

White spot syndrome virus (WSSV) was detected by PCR-dot blot hybridization in rotifer resting eggs from shrimp Penaeus chinensis culture-pond sediments. It was also detected in rotifers hatched from those eggs. Surface disinfection before analysis indicated that WSSV was probably present within the resting eggs. Results suggested that rotifer resting eggs may be an overwintering reservoir for WSSV in shrimp ponds.

The change of population density, the ratio of mictic females and eggs of rotifer Brachionus calyciflorus, cultured in the synthetic medium containing different concentrations of vitamin E, were observed at 15, 25 and 30 degree C, respectively. Rotifer Brachionus calyciflorus was hatched from resting eggs collected from the sediments in bottom of East Lake (China, Wuhan, 114 degree 23'E, 30 degree 33'N). A neonate rotifer hatched from resting egg was transferred into flask containing inorganic medium described by Gilbert (1963). Stock rotifers were fed on Chlorella pyrenoidosa, which was grew in the HB sub(4) medium with light intensity about 5,000lx provided by 8 cool-white fluorescent lamps (16:8 h light: dark cycle; temperature at 25 degree C) in the incubator. Before feeding, algae in log phase of growth were harvested, centrifuged at 4,000 rpm for 5 minutes, rinsed with HB sub(4) medium with 3 times and resuspended in rotifer culture medium. Two neonate rotifers were placed into test tube, each tube containing 10ml of C. pyrenoidosa suspension (2 x 10 super(6) cells/ml diluted with rotifer culture medium. Five different concentration of vitamin E (0 (as control group), 20, 40, 80 and 100ng/ml) were added into each test tube, respectively, Light intensity and photoperiod as the same as above described. The experiment was designed at three temperatures 15, 25 and 30 degree C. The test rotifers were checked, counted and transferred into new rotifer culture medium every 24 hours. The mictic female, amictic female, mictic egg, amictic egg and male were distinguished by the method described by Paloheimo (1974).

Trade-offs between defense and other fitness components are expected in principle, and can have major qualitative impacts on ecological dynamics. Here we show that such a trade-off exists even in the simple unicellular alga Chlorella vulgaris. We grew algal populations for multiple generations in either the presence ('grazed algae') or absence ('non-grazed algae') of the grazing rotifer Brachionus calyciflorus, and then evaluated their defense and competitive abilities. Grazed algae were better defended, yielding rotifer growth rate 32% below that of animals fed non-grazed algae, but they also had diminished competitive ability, with a growth rate under nutrient-limiting conditions 28% below that of non-grazed algae. Grazed algae also had a smaller cell size and were more concentrated in carbon and nitrogen. Thus, C. vulgaris genotypes vary phenotypically in their position along a trade-off curve between defense against grazing and competitive ability. This genetic variation underlies rapid algal evolution that significantly alters the ecological predator-prey cycles between rotifers and algae.

Trade-offs between defence and other fitness components are expected in principle, and can have major qualitative impacts on ecological dynamics. Here we show that such a trade-off exists even in the simple unicellular alga Chlorella vulgaris. We grew algal populations for multiple generations in either the presence ('grazed algae') or absence ('non-grazed algae') of the grazing rotifer Brachionus calyciflorus, and then evaluated their defence and competitive abilities. Grazed algae were better defended, yielding rotifer growth rate 32% below that of animals fed non-grazed algae, but they also had diminished competitive ability, with a growth rate under nutrient-limiting conditions 28% below that of non-grazed algae. Grazed algae also had a smaller cell size and were more concentrated in carbon and nitrogen. Thus, C. vulgaris genotypes vary phenotypically in their position along a trade-off curve between defence against grazing and competitive ability. This genetic variation underlies rapid algal evolution that significantly alters the ecological predator-prey cycles between rotifers and algae.