Recent Publications

on or concerning rotifers

In terms of biodiversity, Brazilian inland waters are of enormous global significance for Algae (25% of the world's species), Porifera (Demospongiae, 33%), Rotifera (25%), Cladocera (Branchiopoda, 20%), and fishes (21%). Threatened freshwater species include 44 species of invertebrates (mostly Porifera) and 134 fishes (mostly Cyprinodontiformes, Rivulidae), primarily distributed in south and southeastern Brazil. Reasons for the declines in biodiversity in Brazilian inland waters include pollution and eutrophication, siltation, impoundments and flood control, fisheries, and species introductions. These problems are more conspicuous in the more-developed regions. The majority of protected areas in Brazil have been created for terrestrial fauna and flora, but they also protect significant water bodies and wetlands. As a result, although very poorly documented, these areas are of great importance for aquatic species. A major and pressing challenge is the assessment of the freshwater biodiversity in protected areas and surveys to better understand the diversity and geography of freshwater species in Brazil. The concept of umbrella species (e.g., certain migratory fishes) would be beneficial for the protection of aquatic biodiversity and habitats. The conservation and improved management of river corridors and associated floodplains and the maintenance of their hydrological integrity is fundamental to preserving Brazil's freshwater biodiversily and the health of its aquatic resources.

In this study totally 25 rotifer species, 3 cladocerus species, and 2 copepoda species were identified in Ova Stream. Among zooplankton rotifer species were dominant. Population densities of planktonic organisms were calculated as individual per cubic meter and the relationship of the planktonic organisms with physicochemical parameters was determined applying canonical correspondence analysis (CCA). Also diversity index has been calculated according to the sampling stations. According to the results, the diversity index changes between stations and sampling time. The CCA results show that the rotifer species Keratella, Notholca showed negative correlation with the increasing chemical parameters and temperature but Brachionus, Mytilina, Colurella, and Testudinella have positive correlation with increasing temperature.

To describe past changes in trophic structure, analyses were conducted of zooplankton (Cladocera, Rotifera) assemblages recovered in a Pb-210 dated sediment core from a shallow brackish lake exposed to several fish kill episodes during the 20(th) century. A weighted-averaging zooplankton-based transfer function was applied to infer planktivorous fish densities (PL-CPUE) and to elucidate the potential of identifying fish kill incidents using sedimentary subfossils. The stratigraphical record showed a shift during the 20(th) century. The cladoceran community structure changed from high abundance of macrophyte-associated taxa and chydorids, characteristic of clear water conditions, towards a community composed mainly by sediment-associated taxa, small-sized pelagic taxa as well as rotifers and chydorids, characteristic of eutrophic turbid conditions. Coinciding with these changes, the mean size of Daphnia ephippia decreased while inferred PL-CPUE increased. The results point towards progressive eutrophication with additional impact of salinity. Reduced temporal resolution of the sediment record made identification of fish kill incidents difficult. The indications of high fish planktivory and a decline in macrophyte abundance are consistent with anecdotal observations of past fish investigations and contemporary data. The study demonstrates the usefulness of applying zooplankton subfossils to detect long-term change, in the trophic structure of brackish lakes in the pas,, In addition, it draws attention to the difficulties of using sediment records to highlight short-term events, such as fish kills, in shallow wind-impacted takes.

Subfossil zooplankton assemblages (Cladocera 22 taxa, Rotifera I taxon) were identified from the surface sediments of 36 shallow (median depth = 0.7 m) Danish coastal brackish lakes differing in epilimnic salinity (SAL, range 0.2-17.4parts per thousand), summer-mean total phosphorus (TP, 27-327 mug l(-1)) and total nitrogen (TN, 0.850-2.629 mg l(-1)), as well as in submerged macrophyte coverage and planktivorous fish density (PL-CPUE). Cladoceran species richness declined significantly with increasing SAL, TP and TN, while no significant correlation was found to either PL-CPUE, macrophyte coverage or lake surface area. Bonferroni-adjusted forward selection within canonical correspondence analysis (CCA) showed that 22.1% of the variation in zooplankton data was explained by PL-CPUE, SAL and TP uniquely; each variable explaining an almost equally significant amount of variation in the zooplankton data. Predictive models to infer PL-CPUE, SAL and TP were developed using variance weighted-averaging (WA) procedures. Almost similar values of boot-strapped coefficient of determination (r(boot-strapped)(2) 0.22-038) were produced by the WA inference models of PL-CPUE, SAL and TP, while the inference models of TP produced the lowest boot-strapped root-mean-squared-error of prediction (RMSEPboot-strapped 0.29-0.36 log(TP + 1), mug l(-1)). Yet, zooplankton TP and SAL optima (WA) were strongly correlated (r(2) = 0.46), while PL-CPUE optima (WA) were independent of both TP and SAL optima, indicating that only the PL-CPUE inference models are suitable for making reconstructions.

The genomes of virtually all sexually reproducing species contain transposable elements. Although active elements generally transpose more rapidly than they are inactivated by mutation or excision, their number can be kept in check by purifying selection if its effectiveness becomes disproportionately greater as their copy number increases. In sexually reproducing species, such synergistic selection can result from ectopic crossingover or from homologous recombination under negative epistasis. In addition, there may be controls on transposon activity that are associated with meiosis. Because a sexual lineage that abandons sex must lack such mechanisms, it may be driven to extinction by the unchecked proliferation of deleterious transposons inherited from its sexual progenitor. An important component of the evolutionary advantage of sex over asex may therefore lie in the ability of sex, despite facilitating the spread of deleterious elements within interbreeding populations, also to restrain their intragenomic proliferation. (C) 2004 Wiley Periodicals, Inc.

The aim of this study was to determine the relative importance of the different processes/mechanisms by which the toxic haptophyte Prymnesium parvum, cultured under different nutrient conditions, affects non-toxic phytoplankton competitors and microzooplankton grazers. P. parvum was cultured under steady-state growth in different nutrient conditions: nitrogen depleted (-N), phosphorus depleted (-P) and balanced nitrogen and phosphorus (+NP). Cells from each nutrient condition and culture cell-free filtrates, alone and combined with non-toxic prey (Rhodomonas salina), were used as food for the rotifer Brachionus plicatilis. An additional experiment was carried out to test the effect of P. parvum cells and culture cell-free filtrate on R. salina. The highest haemolytic activity values were achieved by -P F parvum cultures, followed by -N. However, the negative effect of R parvum on R. salina and rotifers did not correlate with haemolytic activity but with the number of P. parvum cells. -N-cultured P. parvum were the most toxic for both R. salina and rotifers, followed by +NP. Therefore, haemolytic activity is not a good indicator of the total potential toxicity of R parvum. The growth rate of R. salina was negatively affected by cell-free filtrates but the effect of P, parvum predation was greater. Rotifers fed on both toxic and non-toxic algae, indicating that they did not select against the toxic alga. The P. parvum cell-free filtrate had an effect on B. plicatilis, although this was weak, B, plicatilis was also indirectly affected by P. parvum due to the negative effects of the toxic alga on their prey (R. salina). However, the greatest negative effect of P. parvum on the rotifers was due to ingestion of the toxic cells. Therefore, the phytoplankton competitor R. salina is more affected by P. parvum predation and the grazer B. plicatilis is more affected by ingestion of the toxic cells, the effects of excreted compounds being secondary.

Attempts were made to overcome too-low reproductive output in the 48-h short-chronic microbiotest with the rotifer Brachionus calyciflorus fed with microalgae (Pseudokirchneriella subcapitata) from algal beads older than 4 months (Chemosphere 50 (2002a) 365). Prefeeding of freshly hatched rotifers prior to the start of the actual growth experiments resulted in a satisfactory reproduction (i.e., an intrinsic growth rate r > 0.65), even with subsequent feeding of the rotifers with microalgae from beads stored up to 1 year. Rotirich is an attractive alternative inert food compared with the mixture of microalgae and Spirulina, originally used to prefeed the rotifers. When the rotifers were prefed for 2 h with 30 mug/mL Rotirich, it was then not necessary to add Spirulina to the microalgal food from beads. The above findings are a substantial simplification of the testing procedure of the new short-chronic "culture/ maintenance-free" Rotoxkit microbiotest. (C) 2003 Elsevier Inc. All rights reserved.

The effect of dietary a-tocopherol (alpha-T; vitamin E) on the performance of striped trumpeter larvae was assessed using a dose-response design. Five tuna oil/lecithin/water emulsions containing between 0% and 4% (40 mg g(-1)) dry weight (DW) of alpha-T were fed to rotifers, resulting in rotifer alpha-T concentrations between 114 and 1040 mu g g(-1) DW. These rotifers or a reference diet of rotifers enriched with AlgaMac 2000 (AM) were fed to larvae from first feeding at 5 days post-hatch (dph) until 23 dph. In larvae fed the emulsion-enriched rotifers, tissue concentrations of alpha-T were correlated to dietary concentrations. Larvae at 5 dph contained 276 mu g alpha-T g(-1); concentrations in most larvae had reduced at 23 dph (to between 121 and 225 mu g alpha-T g(-1)) except for those fed highest alpha-T, which contained 356 mu g g(-1). Larval weight at 20 dph, and length at 14 and 23 dph were positively correlated with dietary alpha-T concentration. Interpolation of data from the regression curves showed that higher dietary alpha-T (i.e. >= 437 mu g alpha-T g(-1)) gave a maximum 7% increase in larval length and a maximum of 10% increase in weight. Larval survival was extremely variable (average 37.0 +/- 30.1%). Though not statistically significant, average survival was apparently higher (48.4 +/- 28.2%) in larvae fed diets containing >= 437 mu g alpha-T g(-1) than those fed diet with lower alpha-T, i.e. <= 144 mu g alpha-T g(-1) (25.6 +/- 30.3%), with larvae fed 221 mu g alpha-T g(-1) having intermediate survival (37.2 +/- 32.3). (c) 2005 Elsevier B.V. All rights reserved.

Differences between zooplankton structure (species abundance and size distribution) and dynamics of permanent and temporary basins of a Mediterranean salt marsh (Emporda Wetlands, NE Spain) were analysed by means of taxon-based and size-based approaches. These basins are shallow bodies of water which are occasionally connected. They were isolated after water retreat from a broadly flooded, low-lying area close to the open sea. Although temporary and permanent basins show no differences in the most abundant zooplankton species, they differ in their zooplankton diversity, temporal pattern and size structure. The zooplankton assemblages of temporary basins exhibit a temporal pattern with six phases, which are conditioned to the hydrological cycle, each one dominated by one species, whereas in the permanent basin this temporal pattern shows only two phases. Zooplankton size distribution of the temporary basins is dominated by large sizes (copepodites and copepods) while the permanent basin is dominated mainly by small sizes (rotifera and nauplii of copepods). In the temporary basins, the shape of the biomass size spectrum changes according to the hydrological cycle and reflects the dynamics of the ecological interactions among zooplankton species. Differences in the zooplankton composition and dynamics of the permanent basin are not a consequence of water permanence but of the ecological interactions among species involved. The presence of a stable fish population in the permanent waters may explain the high values of zooplankton diversity and the low densities of large zooplankton.

We compared the life history traits of unfertilized mictic females (UMF) and fertilized mictic females (FMF) in two strains of the freshwater rotifer Brachionus calyciflorus obtained from Qingdao and Wuhu cities of China and cultured them at three different algal concentrations (2.0, 5.0 and 8.0 x 10(6) cells/ml). Food concentration significantly affected the duration of the post-reproductive period and the egg volume of UMF as well as the duration of the pre-reproductive period, the egg volume, and the reproductive investment of FMF of the Qingdao strain. Food also influenced the pre-reproductive period, the mean life span, the egg volume, and the reproductive investment of UMF and IMF of the Wuhu strain. At the various food concentrations, there were also significant differences in many of the life history characteristics between the two strains of rotifers.

We describe a terrestrial faunal community including only Tardigrada and Rotifera, present on inland nunataks of Ellsworth Land, Antarctica (similar to 75 degrees-77 degrees S, 70 degrees-73 degrees W). The fauna is exceptional in its simplicity, including five tardigrade species (three new to science) and at least two rotifer species, which comprise two consumer trophic levels. Nematode worms, the most important element of the simplest faunal communities previously reported worldwide (from the Ross Sea Dry Valley region of continental Antarctica), and micro arthropods, otherwise represented in all known Antarctic terrestrial communities, are absent. The tardigrade community composition shows affinity with the continental Antarctic fauna, with which it shares three species. The remaining two species are unique to Ellsworth Land and may suggest a prolonged existence as a distinct biogeographical

The sediment record of the fauna of Ace Lake, a saline meromictic lake in the Vestfold Hills, Antarctica, consists of copepod eggs, spermatophores and exoskeletal fragments, rotifer and tintinnid loricae, and foraminiferal and folliculinid tests. The relative abundance of these remains, along with other characteristics of the core, allows the development of a coherent picture of the progress of Ace Lake from a species-poor, freshwater lake early in the Holocene to a biodiverse marine basin following a marine transgression. Subsequent sea level fall reformed Ace Lake as a saline lake and productivity initially increased after isolation. After a major event, possibly associated with overturn of the meromictic lake, biodiversity and productivity decreased, and have continued to do so until the present. (c) 2005 Elsevier B.V. All rights reserved.

Two of the principal explanations for regional population synchrony, largescale environmental variability and dispersal, have received considerable theoretical attention. Although time series analysis has helped to validate the relative importance of these two explanations, very little of this theory has been confirmed by experiment. Here, we demonstrate the dual synchronizing effect of dispersal and temporal environmental variation. We used an experimental model system based on the rotifer Brachionus calyciflorus and its algal prey Chlorella vulgaris. We constructed temporal prey fluctuations with two periodic components that matched the generation time and life span of the rotifer. By varying the amplitude of these two periods we created prey variability with "white" (both periods had equal power) and "red" (the longest period had greatest power) spectra. In the absence of dispersal only the red fluctuations induced synchrony in the population dynamics of the rotifer. Dispersal had a strong and rapid synchronizing effect. The combination of red (but not white) fluctuations and dispersal resulted in the highest levels of synchrony. These results confirm the predictions of recent theory, but they also suggest that the temporal structure of environmental variability determines its capacity to synchronize population dynamics over large spatial scales.

We analyzed meta-community structure of bdelloid rotifers colonizing mosses along an 80 meter section of Rio Valnava in NW Italy. Bdelloid rotifers are small animals living associated with a substratum; colonization
in bdelloids can be produced by active animals moving along the riverbed, or by passive dormant propagules, moved by wind. To detect which kind of colonization might be stronger at different spatial scales, we designed a spatially nested sampling experiment at three hierarchical levels: (1) single sample, (2) 10 communities inside each pool, (3) complete section of 10 pools. Assessing species richness and species similarity of communities, and coherence and nestedness of bdelloid meta-communities, we found that different forces may drive species composition at different spatial scales: at the largest scale, colonization of propagules may over-ride direct dispersal between pools, while at the scale of the single pool, differential movements of species give a nested structure to the meta-communities. The number of species increased as the level of analysis increased, even though this study was carried out along only a small stream section.

Garcia-Roger, E. M., M. J. Carmona, and M. Serra. 2005. Deterioration patterns in diapausing egg banks of Brachionus (Muller, 1786) rotifer species. Journal of Experimental Marine Biology and Ecology 314: 149-161.

Rotifers are cyclical parthenogens that produce sexual diapausing eggs at some stage in their life cycle. These eggs are encysted embryos that remain viable for extended periods in lake and pond sediments, thus acting as an egg bank with many ecological and evolutionary consequences. Despite its importance to rotifer evolution, there are no studies on resting egg deterioration and associated processes in natural environments. In this study, more than 4000 diapausing eggs of species from the Brachionus plicatilis complex, which includes several closely related cryptic species, were collected from different sediment depths in 15 ponds in eastern Spain and were classified according to three features thought to be related to their viability: shell integrity, embryo size, and embryo colour. A positive association was found between embryo size and hatching success in those eggs having an intact shell. Diapausing eggs that showed good shell integrity and no more than a 25% reduction of multinuclear embryo maximum size were classified as healthy and 98.9% hatched. Darkening of diapausing egg embryo was an indicator of viability loss. A decreasing frequency of healthy-looking diapausing eggs was observed with increasing sediment depth, although some exceptions were found. (C) 2004 Elsevier B.V. All rights reserved.


Geng, H., P. Xie, D. G. Deng, and Q. Zhou. 2005. The rotifer assemblage in a shallow, eutrophic Chinese lake and its relationships with cyanobacterial blooms and crustacean zooplankton. Journal of Freshwater Ecology 20: 93-100.

Rotifer assemblage in the subtropical eutrophic Lake Chaohu was investigated monthly from September 2002 to August 2003. Forty-nine species belonging to 18 genera and 14 families were recorded. The highest densities of rotifer were observed during summer when there were heavy cyanobacterial blooms. There was a significant positive correlation between total rotifer density and the biomass of cyanobacteria. However, no correlations were found between the densities of rotifer and crustacean zooplankton, possibly owing to the paucity of large-bodied planktonic crustaceans. It is likely that the occurrence of cyanobacterial blooms not only caused the shift of dominant crustacean zooplankton from large species to smaller ones but also weakened the negative interaction between crustaceans and rotifers.


Gray, D. K., S. A. Bailey, I. C. Duggan, and H. J. MacIsaac. 2005. Viability of invertebrate diapausing eggs exposed to saltwater: implications for Great Lakes' ship ballast management. Biological Invasions 7: 531-539.

International shipping has been the dominant vector of nonindigenous species introductions to the Laurentian Great Lakes over the past century. Apparent ballast-mediated invasions have been recorded in recent years, despite the implementation of voluntary ballast water exchange regulations in 1989. Since unregulated 'no-ballast-on-board' vessels currently dominate inbound traffic to the Great Lakes, it has been proposed that live or dormant organisms contained in residual ballast of these vessels may be partially responsible for recent invasions. Alternatively, euryhaline species may pose a significant invasion threat because they can potentially survive ballast exchange. In this study, we explored whether exposure to open-ocean water (32&PTSTHOUSND;) reduced the viability of invertebrate diapausing eggs in ballast sediments. Sediments collected from three transoceanic ships and from three freshwater habitats were exposed to open-ocean seawater. Egg viability, assessed as the abundance of taxa hatched between exposed and unexposed sediments, was not affected by saltwater exposure in any experiment. Species richness of hatched diapausing eggs was reduced by saltwater exposure in only one of seven trials. Our results indicate that oligostenohaline zooplankton may pose an invasion risk because their diapausing eggs are largely resistant to exposure to open-ocean saltwater.


Halkett, F., J. C. Simon, and F. Balloux. 2005. Tackling the population genetics of clonal and partially clonal organisms. Trends in Ecology & Evolution 20: 194-201.

Many clonal organisms experience occasional events of sexual recombination, with profound consequences for their population dynamics and evolutionary trajectories. With the recent development of polymorphic genetic markers and new statistical methods, we now have an unprecedented ability to detect recombination in organisms that are thought to reproduce strictly, or essentially asexually. However, it is not always obvious which methodology to apply. Consequently, biologists might decide how to analyse their data without clear guidelines. Here, we discuss the available methods, focusing on those best suited when working with limited genetic information, such as a few genetic markers or DNA sequences. We conclude by commenting on the prospects offered by some recent conceptual advances and the access to high throughput technologies in an increasing number of model organisms.


Hampton, S. E. 2005. Increased niche differentiation between two Conochilus species over 33 years of climate change and food web alteration. Limnology and Oceanography 50: 421-426.

Long-term data from Lake Washington are used to ask whether zooplankton population dynamics can be predicted on the basis of abiotic gradients and potential food resources. I used Dynamic Linear Models to examine effects of fluctuations in temperature and five algal groups on population dynamics of two rotifer species over a 33-yr period in which climate has warmed, anthropogenic nutrient loading has changed dramatically, and Daphnia has become established. Dynamics of the colonial rotifers Conochilus hippocrepis and Conochilus unicornis were both best predicted by temperature and the density of single-celled bacterio- and phytoplankton smaller than 10 mu m, but their seasonal peaks have become dramatically offset toward fall and spring, respectively, in recent years. Both species have been extirpated from the summer months in which they once flourished, seemingly because of midsummer declines in their food resources, which have been depressed by Daphnia since its establishment. However, climate warming has increased the length of the plankton growing season in Lake Washington, such that spring and fall offer greater abundance of food resources for Conochilus, offsetting modern exclusion of Conochilus from midsummer months. Additionally, greater distinction in temporal niches presumably has reduced possibilities for intrageneric competition, and both Conochilus species have achieved higher mean annual abundances in recent years.


Hunt, R. J., and V. F. Matveev. 2005. The effects of nutrients and zooplankton community structure on phytoplankton growth in a subtropical Australian reservoir: An enclosure study. Limnologica 35: 90-101.

Patterns of zooplankton-phytoplankton interactions in Subtropical lakes of the Southern Hemisphere may deviate from those established for north-temperate lakes. We tested the responses of phytoplankton growth to different community structures of zooplankton and nutrient enrichment in a Subtropical Australian reservoir for the prediction of potential outcomes of lake biomanipulation. Two zooplankton communities were created in lake enclosures over 4 weeks: a rotifer-dominated community developed in the presence of planktivorous fish (Hypseleotris spp,) and a Ceriodaphnia-dominated community developed in the absence of fish. Biomass gradients of both communities were established in 20 L containers and several separate containers received no additions (controls) or were enriched with nitrogen and/or phosphorus. The growth rate of total phytoplankton significantly increased in response to nutrient enrichment, indicating nutrient limitation. Most phytoplankton taxa were not markedly affected by grazing or either zooplankton community. However, both communities had significant stimulatory effects on the growth of inedible chlorophytes. The ability of zooplankton grazing to negatively affect phytoplankton growth during the summer was counteracted regardless of zooplankton community structure, possibly by nutrients regenerated by zooplankton. We hypothesise that in the subtropical system studied, changes in food web nutrient recycling may be more important for the outcome of biomanipulation than grazing impacts. (C) 2005 Elsevier GmbH. All rights reserved.


Ignoffo, T. R., S. M. Bollens, and A. B. Bochdansky. 2005. The effects of thin layers on the vertical distribution of the rotifer, Brachionus plicatilis. Journal of Experimental Marine Biology and Ecology 316: 167-181.

Microscale patches of resources occur in both the horizontal and vertical dimensions, and in the latter case are referred to as thin layers. These layers may affect ecological processes like behavior, predation, growth and reproduction in phytoplankton and zooplankton. The objective of this study was to determine possible effects of physical and biological thin layers on the vertical distribution and diel vertical migration of the rotifer Brachionus plicatilis. We used four, 2 m tall, experimental tanks fitted with video cameras which panned the vertical extent of each tank and enabled us to sample on the centimeter scale. The experimental tanks consisted of a thin layer (25 cm thick) of Nannochloropsis oculata, whereas control tanks consisted of homogeneously distributed algae. Rotifers aggregated in the thin layers of N. oculata, and dispersed (becoming evenly distributed) after depleting the algae within the thin layer (ca. 6 h). In contrast, rotifer aggregation in the physical thin layer of control tanks was shorter in duration (ca. 2.5 h) and rotifers were homogenously distributed for the remainder of the experiment despite persistent salinity stratification. No signs of diel vertical migration were noted in either experimental or control tanks. A second set of experiments was run to examine the response of rotifers to a choice of food, i.e., thin layers of the diatom, Skeletonema costatum versus the eustigmatophyte, N. oculata. For the choice experiments, two thin layers were created, one with each food option. Our results suggest that B. plicatilis aggregates and feeds preferentially on N. oculata over S. costatum. In both types of experiments rotifers responded, in terms of distribution, to thin layers of algae within the first half-hour of introduction and remained in the thin layers until the food source was depleted. Our results suggest that rotifers may be important grazers on thin layers because of their ability to quickly locate and take advantage of ephemeral food patches. (c) 2004 Elsevier B.V. All rights reserved.


Kurbatova, S. A. 2005. Response of microcosm zooplankton to acidification. Biology Bulletin 32: 85-92.

Zooplankton community transformation in response to soft water acidification was studied in two experimental series using the microcosm method. The dynamics of total abundance, changes in the proportions of the main zooplankton groups, stability of the dominant complex, and species diversity were evaluated. Zooplankton population proved to decrease at all studied low pH (5-6, 4-5, and 3-4) within the first two weeks relative to the control. At water pH 5-6, either Rotifera-Copepoda or Cladocera-Copepoda zooplankton complex was established depending on the initial community composition; while at pH 4-5, Copepoda predominated in the established zooplankton community. The community edificator species was replaced at pH 4-5. The lowest diversity index was also observed at this pH (1.0-1.5 bit/ind.). In addition, the proportion and absolute population of copepod nauplii and cladoceran Scapholeberis mucronata increased at low pH. A decrease in water pH to 3-4 proved to be disruptive for the zooplankton community.


Linhartova, S., J. Linhart, and V. Uvira. 2005. Benthic rotifers and flow velocity in two low-order streams. Biologia 60: 151-158.

The primary objective of this study was to determine the relationship between moss-dwelling and the surrounding mineral substrata-dwelling rotifers with local flow velocity in two low-order streams. Differences in rotifer distribution between riffle and pool areas of the studied streams (the Bystrice, Czech Republic and the Oberer Seebach, Austria) were also assessed. Bdelloid rotifers showed a positive or no significant relationship with local flow velocity within Fontinalis antipyretica and no clear relationship was observed within the mineral bed. However, monogonont rotifers were related to local flow velocity negatively or no significance was found within moss. Our data on the distribution of moss-dwelling monogononts in riffles and pools indicate that monogonont rotifers avoid the erosive impact of higher flow velocity in low-flow areas (pools). No clear relationship was observed within the mineral bed, as in bdelloids. The introduced B/M ratio (i.e., Bdelloidea : Monogononta abundance ratio) seemed to explain the relationship between rotifers and flow velocity better and it was positively dependent on velocity for moss-dwelling rotifers. We found no clear relationship of the B/M ratio with local flow velocity within the mineral substrata. Probably, mineral substrata-dwelling rotifers and/or the mineral bed itself responded differently to flow conditions compared to the exposed clumps of F. antipyretica.


Lowe, C. D., S. J. Kemp, A. D. Bates, and D. J. S. Montagnes. 2005. Evidence that the rotifer Brachionus plicatilis is not an osmoconformer. Marine Biology 146: 923-929.

The rotifer Brachionus plicatilis is euryhaline ( growing between 2 and 97 ppt) and has previously been considered an osmoconformer. We suggest that B. plicatilis is an osmoregulator, exhibiting a pattern of Na+/ K+ ATPase activity in response to salinity consistent with that of other osmoregulating euryhaline invertebrates. To examine salinity tolerance, growth rates between 5 and 60 ppt were determined. The activity of Na+/ K+ ATPase was examined, over the same range of salinities, by measuring ATPase activity in rotifer homogenates in the presence and absence of a Na+/ K+ ATPase inhibitor. Maximum specific growth rate (0.95 day(-1)) occurred at 16 ppt, highest mean amictic eggs per female (1.41) occurred at 20 ppt, and both parameters decreased rapidly as salinity increased. Egg development time was constant with salinity at 0.92 days. The activity of Na+/ K+ ATPase per milligram protein increased from 3.9 mu mol h(-1) at 5 ppt to 6.8 mu mol h(-1) at 50 ppt and accounted for 15 and 30% of total ATPase activity, respectively. We suggest that these observations are consistent with increasing stress at high salinities and the occurrence of a hypo-osmoregulatory response. Given the high ATP consumption of Na+/ K+ ATPase at high salinities, it is possible that a proportion of the corresponding decreases in growth rate and egg production are a direct cost of regulation.


Makridis, P., S. Martins, T. Vercauteren, K. Van Driessche, O. Decamp, and M. T. Dinis. 2005. Evaluation of candidate probiotic strains for gilthead sea bream larvae (Sparus aurata) using an in vivo approach. Letters in Applied Microbiology 40: 274-277.

Aims: The aim of this study was to evaluate the effect of six bacterial strains on gilthead sea bream larvae (Sparus aurata). Methods and Results: Six bacterial strains isolated from well-performing live food cultures were identified by sequencing fragments of their 16s rDNA genome to the genus level as Cytophaga sp., Roseobacter sp., Ruergeria sp., Paracoccus sp., Aeromonas sp. and Shewanella sp. Survival rates of gilthead sea bream larvae transferred to seawater added these bacterial strains at concentrations of 6 +/- 0.3 x 10(5) bacteria ml(-1) were similar to those of larvae transferred to sterilized seawater and showed an average of 86% at 9 days after hatching, whereas, survival rates of larvae transferred to filtered seawater were lower (P < 0.05), and showed an average of 39%, 9 days after hatching. Conclusion: Several bacterial strains isolated from well-performing live food cultures showed a positive effect for sea bream larvae when compared with filtered seawater. Significance and Impact of the Study: The approach used in this study could be applied as an in vivo evaluation method of candidate probiotic strains used in the rearing of marine fish larvae.


Mielbrecht, E. E., M. F. Wolfe, R. S. Tjeerdema, and M. L. Sowby. 2005. Influence of a dispersant on the bioaccumulation of phenanthrene by topsmelt (Atherinops affinis). Ecotoxicology and Environmental Safety 61: 44-52.

Chemical dispersants enhance oil spill dispersion by forming water-accommodated micelles with oil droplets. However, how dispersants alter bioavailability and subsequent bioaccumulation of hydrocarbons is not well understood. Thus, the goal was to investigate the influence of a chemical dispersant on the disposition (uptake, biotransformation, and depuration) of a model hydrocarbon, [C-14]-phenanthrene ([C-14]PHN), by larval topsmelt (Atherinops affinis). Exposure was via aqueous-only or combined dietary and aqueous routes from a water-accommodated fraction (WAF) of Prudhoe Bay Crude Oil (PBCO) or a WAF of Corexit 9527-dispersed PBCO (DO). Trophic transfer was measured by incorporating into exposure media both a rotifer (Brachionus plicatilis) as food for the fish and a phytoplankton (Isochrysis galbana) as food for the rotifers. Short-term (<= 4 h) bioconcentration of PHN was significantly decreased in topsmelt when oil was treated with dispersant (P < 0.05), but differences diminished after 12 h. When trophic transfer was incorporated, PHN accumulation was initially delayed but after 12 h attained similar levels. Dispersant use also significantly decreased the proportion of biotransformed PHN (as 9-phenanthrylsulfate) produced by topsmelt (P < 0.05). However, overall PHN depuration was not affected by dispersant use. Thus, chemical dispersant use in oil spill response may reduce short-term uptake but not long-term accumulation of hydrocarbons such as PHN in pelagic fish. (c) 2004 Elsevier Inc. All rights reserved.


Nandini, S., P. Ramirez-Garcia, and S. S. S. Sarma. 2005. Seasonal variations in the species diversity of planktonic rotifers in Lake Xochimilco, Mexico. Journal of Freshwater Ecology 20: 287-294.

We collected rotifers during one year (2002-2003) from four different sites in Lake Xochimilco and analyzed the species diversity. We found on an average 25-30 species co-existing at any one site, and rotifer species density was highest in the summer months. The common genera found throughout the year were Brachionus, Keratella, Polyarthra, Trichocerca, Filinia and Asplanchna, and we often found six to eight species of Brachionus in the same sample. Keratella cochlearis and K. tropica were often found together, as were Trichocerca similis, T. pusilla and T. cylindrica. The genus Asplanchna was represented almost exclusively by A. brightwelli.


Pouchkina-Stantcheva, N. N., and A. Tunnacliffe. 2005. Spliced leader RNA-mediated trans-splicing in phylum Rotifera. Molecular Biology and Evolution 22: 1482-1489.

In kinetoplastids, Euglena, and four metazoan phyla, trans-splicing has been described as a mechanism for the generation of mature messenger RNAs (mRNAs): 5'-ends of precursor mRNAs are replaced by a short spliced leader (SL) exon from a small SL RNA. Although the full phylogenetic range is unknown, trans-splicing has not been found in vertebrates, insects, plants, or yeast. In animal groups where it does occur, i.e., nematodes, cnidarians, platyhelminths, and primitive chordates, SL RNAs do not show sequence relatedness across phyla. The apparently sporadic phylogenetic distribution and the lack of SL RNA homology have led to opposing hypotheses on its evolution, involving either an ancient origin followed by loss in multiple lineages or independent acquisition in several taxa. Here we present evidence for the occurrence of trans-splicing in bdelloid rotifers (Bdelloidea, Rotifera). A common 23-nt sequence, representing the SL exon-diagnostic of SL RNA-mediated trans-splicing-was found at the 5'-end of at least 50%-65% of mRNAs from Adineta ricciae and Philodina sp. The trans-splicing pattern in bdelloid rotifers can be unusually complex, as observed in transcripts from a heat shock protein gene, hsp82-1, where the SL exon was spliced to three alternative positions. Bdelloid rotifer SL RNAs were found to be 105 or 106 nt long and comprised the SL sequence, a conserved splice donor site and an intron containing a putative spliceosome-binding motif. Intriguingly, some similarity of rotifer SL RNA sequence and predicted secondary structure was seen to that of the predominant SL1 RNA of nematodes, although it is unlikely that this demonstrates homology. In addition, sequence corresponding to the rotifer SL exon was found at the 5'-end of a number of full-length complementary DNA (cDNA) clones in a rice (Oryza sativa) database. None of these cDNAs gave a close match with homologous plant genes, suggesting that a small but significant portion of the rice expressed sequence tag database represents sequences derived from rotifers. In summary, the description of SL-mediated trans-splicing in Rotifera extends its representation to at least five metazoan phyla, making it increasingly probable that this is a phylogenetically widespread and therefore ancient phenomenon.


Ramesh, M. A., S. B. Malik, and J. M. Logsdon. 2005. A phylogenomic inventory of meiotic genes: Evidence for sex in Giardia and an early eukaryotic origin of meiosis. Current Biology 15: 185-191.

Sexual reproduction in eukaryotes is accomplished by meiosis, a complex and specialized process of cell division that results in haploid cells (e.g., gametes). The stereotypical reductive division in meiosis is a major evolutionary innovation in eukaryotic cells [1], and delineating its history is key to understanding the evolution of sex [2]. Meiosis arose early in eukaryotic evolution, but when and how meiosis arose and whether all eukaryotes have meiosis remain open questions [3]. The known phylogenetic distribution of meiosis comprises plants, animals, fungi, and numerous protists [4]. Diplomonads including Giardia intestinalis (syn. G. lamblia) are not known to have a sexual cycle [5]; these protists may be an early-diverging lineage [6] and could represent a premeiotic stage in eukaryotic evolution. We surveyed the ongoing G. intestinalis genome project data [7] and have identified, verified, and analyzed a core set of putative meiotic genes-including five meiosis-specific genes-that are widely present among sexual eukaryotes. The presence of these genes indicates that: (1) Giardia is capable of meiosis and, thus, sexual reproduction, (2) the evolution of meiosis occurred early, in eukaryotic evolution, and (3) the conserved meiotic machinery comprises a large set of genes that encode a variety of component proteins, including those involved in meiotic recombination.


Ricci, C., M. Caprioli, C. Boschetti, and N. Santo. 2005. Macrotrachela quadricornifera featured in a space experiment. Hydrobiologia 534: 239-244.   pdf

Macrotrachela quadricornifera, a bdelloid rotifer, is the animal model of an experiment scheduled on the International Space Station (ISS). The focus of the experiment is the role of the cytoskeleton during oogenesis and early development. Bdelloids will fly desiccated, be rehydrated on the ISS and cultivated for five generations. We present the outline of the ISS experiment, the expectations and the state-of-the-art of ground-based research run to date on the major topics of the planned experiment: anhydrobiosis and embryogenesis. Anhydrobiosis focuses on two major aspects, storage conditions that enhance recovery rate and comparison of the resistance between dormant and active rotifers to UV radiation and other environmental injuries. Embryogenesis has been approached at the morphological level under ground conditions: developing embryos have been studied by light and confocal microscopes.


Rougier, C., R. Pourriot, T. Lam-Hoai, and D. Guiral. 2005. Ecological patterns of the rotifer communities in the Kaw River estuary (French Guiana). Estuarine Coastal and Shelf Science 63: 83-91.

A study of the rotifer fauna in the Kaw River estuary revealed significant quantitative and qualitative variations as a function of precipitation pattern and resulting hydrology and hydrochemistry. The rainy season (flood period) was characterized by the presence of about one hundred rotifer species of the periphytic continental type, each present at a very low average density (8 to 10 ind l(-1)). Rotifers generally constituted the majority of the zooplankton (above 70%). The dry season (low water period) was characterized by a small number (four) of species of the 'marine coastal' plankton type, showed the highest density peaks (> 500 ind l(-1)). While the fluvial hydrodynamics during the rainy season contributed to a complete mixing of populations across the estuarine zone, the oceanic hydrodynamics during the dry season led to great population instability at the station level. At an annual scale, this estuarine zone is thus an essentially open environment that lacks a clearly-structured rotifer population, and which therefore most likely does not constitute a distinct, internally-functioning ecosystem. (c) 2004 Elsevier Ltd. All rights reserved.


Saygi, Y., and S. Yigit. 2005. Rotifera community structure of Yenicaga Lake, Turkey. Journal of Freshwater Ecology 20: 197-199.

We characterized the Rotifera community in Yenicaga Lake, Turkey between October 1997 and August 1999. Totally, twenty-two rotifer species were found, and their relative dominance showed significant seasonal variations. The most frequently occurring species were Keratella quadrata, Filinia longiseta, Brachionus urceolaris, and Asplanchna priodonta.


Serrano, L., and K. Fahd. 2005. Zooplankton communities across a hydroperiod gradient of temporary ponds in the Donana National Park (SW Spain). Wetlands 25: 101-111.

We studied the influence of hydroperiod on the composition and richness of the zooplankton community in 19 freshwater temporary ponds of the Donana National Park (SW Spain) at different spatial and temporal scales. The study ponds were assigned to three hydroperiod categories (long, intermediate, and short) according to previous hydrologic records. During the study period (October 1996-September 1998), wet phases ranged from 56% to 100% of the study period in the five long-hydroperiod ponds, from 25% to 47% in the 10 intermediate-hydroperiod ponds, and from 5% to 21% in the four short-hydroperiod ponds. A total of 56 crustacean species (27 cladocerans, 11 cyclopoids, 5 diaptomids, 1 harpacticoid, 1 notostracan, 1 anostracan, 1 diplostracan) and 47 rotifer taxa were identified from the 19 ponds. Most zooplankton taxa were widely distributed in the ponds. However, Dapnia longispina was restricted to the long-hydroperiod ponds and Metacyclops minutus to the short-hydroperiod ponds. There was a significant (P < 0.01) positive correlation between the number of zooplankton taxa collected in each pond over the entire study period (or cumulative richness) and the pond wet-phase length (r=0.790 for crustaceans and r=0.862 for rotifers, log-transformed data). However, single collection richness (or number of taxa registered in each pond at each sampling date) was not significantly different among hydroperiod categories (Kruskal-Wallis test, P > 0.05) for either crustaceans or rotifers. On average, single collection richness represented between 30% and 48% of the cumulative richness, and this percentage was significantly lower in the long- than in the short-hydroperiod ponds (Mann-Whitney tests) for crustaceans (P < 0.05) and rotifers (P < 0.01). Our data showed that the effect of hydrologic variability on zooplankton taxon richness depended on the temporal scale of observation; it was weakly affected at a momentary scale and strongly affected in the long-term. A longer hydroperiod implied more chance for change in these fluctuating environments.


Sharma, B. K. 2005. Rotifer communities of floodplain lakes of the Brahmaputra basin of lower Assam (NE India): biodiversity, distribution and ecology. Hydrobiologia 533: 209-221.

The rotifer communities of 15 acidic - alkaline and soft - marginally hard water floodplain lakes of the lower Assam valley of the Brahmaputra river basin, characterized by low ionic concentrations, reveal 164 species (178 taxa) belonging to 39 genera and 20 families and represent the richest biodiversity known to date in these ecotones of the Indian subcontinent. Nine species are new to the Indian Rotifera. Cosmopolitan (59.7%) > pantropical (15.2%) > cosmotropical (12.2%) species dominate the taxocoenosis. Biogeographically interesting elements constitute a notable component (13.4%); important members of this category include six Oriental, two Australasian and seven Palaeotropical species. The examined fauna depicts a tropical character with predominance of Lecane spp. (28.0%). Littoral or periphytic rotifers (76.2%) dominate the planktonic species. Rotifers comprise a dominant qualitative (67-103, 79.1 +/- 11.0 species) and an important quantitative (mean: 41.1-65.9%) component of zooplankton in all floodplain lakes, register a moderate diversity (mean: 2.036-2.642), low dominance (mean: 0.019-0.216) and high evenness (mean: 0.840-0.893). The examined material indicates several interesting acidophilous elements. Richness depicts significant inverse correlation with pH. Water temperature, conductivity, dissolved oxygen and alkalinity record significant direct relationships with the rotifer abundance. Diversity is influenced by abundance and is also directly correlated with water temperature and conductivity. Canonical analysis shows a notable cumulative impact of six abiotic factors on richness, density and diversity.


Sorensen, M. V. 2005. Musculature in three species of Proales (Monogononta, Rotifera) stained with phalloidin-labeled fluorescent dye. Zoomorphology 124: 47-55.

The musculature in the rotifer species Proales daphnicola, P. reinhardti and P. fallaciosa was stained with phalloidin-labeled fluorescent dye and compared using confocal laser scanning microscopy. All three species share several homologous muscle systems, but each systems detailed morphology varies among the species both concerning appearance, number and location. The obtained results were compared with data from other rotifers and it was concluded that the muscles pars coronalis and the corona sphincter probably represent conditions in Ploima or Monogononta, while incomplete circular muscles and dorsal and ventral trunk retractors might be part of the eurotatorian ground pattern.


Sorensen, M. V., H. Segers, and P. Funch. 2005. On a new Seison Grube, 1861 from coastal waters of Kenya, with a reappraisal of the classification of the Seisonida (Rotifera). Zoological Studies 44: 34-43.

On a new Seison Grube, 1861 from coastal waters of Kenya, with a reappraisal of the classification of the Seisonida (Rotifera). Zoological Studies 44(l): 34-43. On occasion of the discovery of a new species of a marine epizoic rotifer of the enigmatic Seisonidae, from Gazi Bay in Kenya, we reassessed the classification of the group. The taxon was until now known to contain only 2 species, viz. Seison nebaliae and S. annulatus, both of which live attached to Crustacea of the genus Nebalia. The new species, Seison africanus sp. nov., was diagnosed by its species-specific trophi morphology and relatively small size. A comparison with the 2 other known seisonid species reveals a sister group relationship between S. africanus sp. nov. and S. nebaliae, based on similarities in trophi structure and, accordingly, an assumed feeding mode and relationship with their hosts. The fundamental differences between these 2 commensal sister taxa and the ectoparasitic S. annulatus prompted a reevaluation of the generic classification of these animals. Accordingly, we propose to reestablish the genus Paraseison Plate, 1887 in order to accommodate P. annulatus (Claus, 1876) (comb. nov.).


Strojsova, M., and J. Vrba. 2005. Direct detection of digestive enzymes in planktonic rotifers using enzyme-labelled fluorescence (ELF). Marine and Freshwater Research 56: 189-195.

A novel enzyme-labelled-fluorescence (ELF) method was applied to natural populations of planktonic rotifers from a eutrophic reservoir. Direct visualisation of rotifers by this new method provided new information about enzymatic activities in situ, including detection and location of enzyme activities. Three fluorogenic substrates were used for the enzyme assay in concentrated (20-60x) samples of the rotifers. After a short (1-3 h) incubation in test tubes, samples were filtered and the rotifers on polycarbonate filters were examined using an epifluorescence microscope. Activity of phosphatases, beta-N-acetylhexosaminidases and lipases were detected in some species that were regularly inspected during two seasons - most frequently in the stomach area, at the corona and, less often, in the mastax area. The results suggest that most of the detected enzymes are connected with the digestive tracts of rotifers. Also, autofluorescence of chlorophyll a enabled visualisation of the digestive tracts of the rotifers and provided additional information on the food (phytoplankton). Enzyme expression did not show any clear seasonal trend. Detection of specific enzymes varied considerably between species of rotifers and between individuals. This variability could be a result of change of feeding behaviour of rotifers in the concentrated samples and also could reflect individual differences among the rotifers in a population, such as feeding activity, age or life stage.


Sugita, H., S. Yamamoto, C. Asakura, and T. Morita. 2005. Occurrence of Listonella anguillarum in seed production environments of Japanese flounder Paralichthys olivaceus (Temminck et Schlegel). Aquaculture Research 36: 920-926.

The present study was undertaken to investigate the distribution of Listonella anguillarum in the rearing water, fish and diets (rotifers) of Japanese flounder (Paralichthys olivaceus). A total of 793 isolates were obtained from the seed production environment of Japanese flounder and 175 out of them were identified as L. anguillarum by biochemical characterization, polymerase chain reaction (PCR) detection for VAH1 haemolysin gene and phylogenetic analysis of 16S ribosomal deoxyribonucleic acids (rDNA) sequences. These results strongly suggested that L. anguillarum is rapidly and accurately identified by the combination of incubation on thiosulphate-citrate-bile salt-sucrose agar at 35 degrees C overnight and PCR detection for the VAH1 haemolysin gene. All flounder specimens and all rotifer samples harboured L. anguillarum at high densities of 6.9 x 10(3)-6.3 x 10(5) colony forming units (CFU) g(-1) and 1.5 x 10(4)-2.3 x 10(6) CFU g(-1), respectively, while as low as 5.0 x 10(0)-2.0 x 10(1) CFU mL(-1) of L. aguillarum were detected in only two of 11 seawater samples, even though no vibriosis occurred in larval and juvenile flounder of tanks. This fact strongly suggests that L. anguillarum is an inhabitant in the seed production environments of Japanese flounder.


Trzcinski, M. K., S. J. Walde, and P. D. Taylor. 2005. Stability of pitcher-plant microfaunal populations depends on food web structure. Oikos 110: 146-154.

Enrichment (increasing K) destabilizes simple consumer-resource interactions, but increasing food web complexity in various ways can remove this paradox of enrichment. We varied resources and number of omnivorous predators (mosquitoes) and tested for effects on the stability (persistence and temporal variability) of microfaunal populations living in pitcher plants. Top-down (omnivorous) effects were destabilizing, decreasing the persistence time of a rotifer, Habrotrocha rosa, and perhaps a microflagellate, Bodo sp. Enrichment effects were more complex, in part due to effects of shredding midges on resource availability, and in part due to interactions with predation. The persistence of Bodo increased with resource availability (more bacteria due to shredding by midges; no paradox of enrichment). Increasing resources by adding ants decreased persistence of H. rosa when mosquitoes were rare (paradox of enrichment), but the effect was reversed in leaves with significant colonization by mosquitoes. Thus, in the microfaunal community of pitcher plants, omnivorous predation tends to be destabilizing, and also tends to remove the paradox of enrichment.


Vignati, D. A. L., T. Dworak, B. Ferrari, B. Koukal, J. L. Loizeau, M. Minouflet, M. I. Camusso, S. Polesello, and J. Dominik. 2005. Assessment of the geochemical role of colloids and their impact on contaminant toxicity in freshwaters: An example from the Lambro-Po system (Italy). Environmental Science & Technology 39: 489-497.

The role of colloids in regulating element transport, behavior, and bioavailability in aquatic systems is now well-established. It appears that further progress in this research field is being slowed by (i) a limited integration between the geochemical and the biological aspects of the research on colloids and (ii) a persistent gap between wellcontrolled laboratory studies and real field situations. This paper presents a simultaneous evaluation of the role of colloids in controlling element environmental fate and bioavailability at the confluence between a major river and a polluted tributary. Fractionation of trace elements among suspended particulate matter, colloids, and true solution suggests that colloids may play a role in the removal of trace elements from the water column to bed sediments during the mixing of the two rivers. Toxicity testing of water samples indicates that, in this specific system, contaminants associated with colloids can contribute to water toxicity for the rotifer Brachionus calyciflorus but not for the green alga Pseudokirchneriella subcapitata. To the best of our knowledge, the results for B. calyciflorus are the first ones pointing to the possible contribution of colloid-bound contaminants to water toxicity in environmental samples. Despite the uncertainties associated with field variability,the results of chemical analysis and toxicity testing show several points of convergence. Following these observations, a few innovative research approaches are suggested to improve the understanding of trace element biogeochemistry in real field situations.


Wang, L. P., T. Yan, R. C. Yu, and M. J. Zhou. 2005. Experimental study on the impact of dinoflagellate Alexandrium species on populations of the rotifer Brachionus plicatilis. Harmful Algae 4: 371-382.

To investigate harmful effects of the dinoflagellate Alexandrium species on microzooplankton, the rotifer Brachionus plicatilis was chosen as an assay species, and tested with 10 strains of Alexandrium including one known non-PSP-producer (Alexandrium tamarense, AT-6). HPLC analysis confirmed the PSP-content of the various strains: Alexandrium lusitanicum, Alexandrium minutum and Alexandrium tamarense (ATHK, AT5-1, AT5-3, ATC102, ATC103) used in the experiment were PSP-producers. No PSP toxins were detected in the strains Alexandrium sp1, Alexandrium sp2. Exposing rotifer populations to the densities of 2000 cells ml(-1) of each of these 10 Alexandrium strains revealed that the (non-PSP) A. tarnarense (AT-6) and two other PSP-producing algae: A. lusitanicum, A. minutum, did not appear to adversely impact rotifer populations. Rotifers exposed to these three strains were able to maintain their population numbers, and in some cases, increase them. Although some increases in rotifer population growth following exposures to these three algal species were noted, the rate was less than for the non-exposed control rotifer groups. In contrast, the remaining seven algal strains (A. tamarense ATHK, AT5-1, AT5-3, ATC102, ATC103; also Alexandrium sp1 and Alexandrium sp2) all have adverse effects on the rotifers. Dosing rotifers with respective algal cell densities of 2000 cells ml-1 each, for Alexandrium spl, Alexandrium sp2, and A. tamarense strains ATHK and ATC103 showed mean lethal time (LT50) on rotifer populations of 21, 28, 29, and 36h, respectively. The remaining three species (A. tamarense strains AT5-1, AT5-3, ATC102) caused respective mean rotifer LT50S of 56, 56, and 71 h, compared to 160 h for the unexposed "starved control" rotifers. Experiments to determine ingestion rates for the rotifers, based on changes in their Chlorophyll a content, showed that the rotifers could feed on A. lusitanicum, A. minutum and A. tamarense strain AT-6, but could graze to little or no extent upon algal cells of the other seven strains. The effects on rotifers exposed to different cell densities, fractions, and growth phases of A. tamarense algal culture were respectively compared. It was found that only the whole algal cells had lethal effects, with strongest impact being shown by the early exponential growth phase of A. tamarense. The results indicate that some toxic mechanism(s), other than PSP and present in whole algal cells, might be responsible for the adverse effects on the exposed rotifers. (C) 2004 Elsevier B.V. All rights reserved.


Yang, C. Y., and J. J. Chou. 2005. A comparative evaluation approach for the classification of rotifers with modified non-parametric kNN. Image and Vision Computing 23: 427-439.

In this study-aimed to achieve optimal accuracy in the classification of rotifers according to the number of eggs carried-several modifications to the basic kNN method have been proposed and assessed. Six distinct kNN rules as well as several additional hybrid models were, in fact, devised or employed and their precision compared. Meanwhile, the data sets used in the evaluation of each of these methods were acquired from rotifer images generated via the shape moments approach. Both the original data sets and the edited ones, formed by removing outliers from the originals, were used in the evaluation of these adjusted models. Through a process of comparative evaluation, several of the modified algorithms proposed-comprising both individual and hybrid models-were found to perform better overall than the classical kNN method. Refinements related to class-size weighting, in particular, were shown to heighten the accuracy of the classical kNN model considerably. Close evaluation of the various models created revealed kNN-CCS and F-kNN-CCS, in their application to the edited data sets, to be the most reliable individual modified and hybrid models respectively, with levels of accuracy greater than 95%. (C) 2004 Elsevier B.V. All rights reserved.