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This review provides a comprehensive summary of the current knowledge on marine zooplankton diversity and distribution, highlighting key advancements and future directions in the field. While the approach used in this review is necessarily broad, focusing on overarching trends and drivers of zooplankton diversity, it emphasizes recent methodological innovations. The review begins with an introduction to zooplankton, tracing the historical development of their research. It then explores the critical roles zooplankton play in ocean ecosystems, climate change, and the global economy. Next, the review examines the environmental and anthropogenic factors influencing marine zooplankton. Finally, it presents a comparison between marine and freshwater zooplankton and concludes with a discussion of the challenges facing current zooplankton diversity research and the presentation of possible directions and implementation strategies for advancing the understanding of zooplankton biodiversity and ecology. [ABSTRACT FROM AUTHOR]

Urbanisation affects not only large ecosystems but also small ones, such as ponds, through changes in environmental parameters. It consequently impacts the biodiversity of all organisms, including zooplankton. However, disturbances due to urbanisation may have different levels of impact on ecosystems. We therefore aimed to determine how different degrees of disturbance and environmental parameters affect zooplankton species diversity and which zooplankton species could indicate the disturbance degree and water quality of tropical urban ponds. We recorded 63 species, namely, 46 species of rotifers and 17 species of cladocerans. The overall species diversity tended to decrease from the low to the high disturbance areas. The level of disturbance, temperature, salinity, phycocyanin and vegetation affected the zooplankton species composition. More common species were found in the low disturbance areas, and among the few species in the highly disturbed areas, the distribution was more specific. We therefore propose that rotifer and cladoceran species be used as bioindicators to indicate water quality and the degree of disturbance. Our study provides significant insights into the relationship between zooplankton and environmental factors in oriental tropical regions and presents a framework for identifying crucial species associated with levels of disturbance, particularly in the habitats of Oriental Asia. [ABSTRACT FROM AUTHOR]

Zooplankton plays a pivotal role in lentic water bodies, linking planktonic primary producers to higher trophic levels and being a cornerstone of the planktonic food web of ponds and lakes. Because of its ease of culture, large size, rich ecology, abundance in northern temperate lakes where limnology is rooted, and the ability to work with clones, Daphnia has, in the last centuries grown to become a key model system in ecology, evolution, and ecotoxicology. Consequently, a vast majority of freshwater zooplankton ecology focuses on the role of Daphnia. While generating essential insights, this has also deviated attention from the broad ecological impact of other zooplankton. Here, we emphasize how other zooplankton taxa have an important impact in nature - often in qualitatively different ways than Daphnia. We illustrate this point by focusing on two key zooplankton functions (herbivory and stoichiometry) and suggest research to capitalize on the success story of mechanistic ecological, eco-evolutionary, and genomic Daphnia work to develop a richer set of model organisms. We currently have the tools to do so and integrating mechanistic insights in multispecies settings would foster a better understanding of the rich diversity and ecology of freshwater zooplankton. [ABSTRACT FROM AUTHOR]

Multicellular organisms and their microbiomes can have a restricted and enduring relationship, sometimes reflected in their phylogenies, called phylosymbiosis. However, in some organisms, such as freshwater zooplankton, these relationships appear to be more flexible and more easily influenced by the environment. Here, we analysed the microbiome of a freshwater flatworm, Stenostomum leucops and sequenced the 16S RNA gene of the microbiota of a strain that was maintained in the laboratory for 12 years. This strain underwent four different cultivation conditions over the past 6 years, and the microbiome was characterised for each of these conditions. In addition, the microbiome of a wild S. leucops population was analysed. The microbiomes were highly variable between populations (Shannon index ranging from 0.26 to 2.06). It was not possible to determine a core microbiome, although Bacillus, Pseudomonas and Ralstonia were the predominant bacteria in populations under stable conditions. Under culture conditions where the water was contaminated with iron, Rhodoferax ferrireducens, a bacterium involved in iron reduction, was the predominant species. Our results are consistent with other studies on freshwater zooplankton. The microbiomes were very flexible and were influenced by the environment. [ABSTRACT FROM AUTHOR]

Increasing chloride concentrations threaten freshwater zooplankton. We questioned the protectiveness of the Canadian Water Quality Guideline for chloride because it is based on individual species studied under laboratory conditions and does not account for potential interactive factors, such as nutrient concentration. We exposed plankton communities to 30 chloride concentration increments for 6 weeks, crossed with either ambient or high nutrient treatments. Total zooplankton abundance, biomass, and richness declined with increasing chloride, with losses observed below the Canadian Water Quality Guideline. Nutrients did not affect the impact of chloride on zooplankton. Phytoplankton and protist responses varied by nutrient level. Under low nutrients, phytoplankton and protist abundance, biomass, and richness increased with chloride. Under high nutrients, phytoplankton and protist abundance and biomass were unaffected while richness decreased with chloride. These results indicate that current water quality guidelines do not sufficiently protect plankton and that nutrient context may alter phytoplankton and protist response. [ABSTRACT FROM AUTHOR]

Non-indigenous species may pose a threat to native ecosystems worldwide. In aquatic environments, invasives may have a negative impact on human food security and livelihoods. Several water fleas (Crustacea: Branchiopoda: Cladocera) are notorious invasive alien species influencing large freshwater lake systems and even inland seas. In the current review, we discuss the state of knowledge regarding non-indigenous species in the Cladocera and their invasiveness potential in different continents. We argue that the potential impacts and occurrence of cladoceran exotics may be higher than generally assumed. We critically review 79 cases from literature sources, involving 61 cladoceran taxa where records outside of their natural distribution ranges were previously interpreted as invasions. We assessed the probability of natural range expansions versus human-mediated introductions and we discuss several major corridors of invasion. We estimate human-mediated transportations for at least 43 taxa (out of 61; ca 70%), while other cases can be seen as natural expansions of their distribution ranges (not necessarily/not likely human-mediated) and/or taxonomical confusion. We confirm non-indigenous presence in recipient regions for at least 41 cladoceran taxa, of which several are true invasives (i.e., with negative impacts on native ecosystems). The majority are zooplankters with effects on pelagic freshwater ecosystems, yet we also report on introductions by littoral taxa. We argue that cryptic introductions of cladocerans are taking place on a global scale, yet they remain under the radar. We highlight several striking case studies, such as the Ponto–Caspian onychopods that have invaded the Baltic Sea and the Laurentian Great Lakes, and several clones of the anomopod genera Daphnia and Bosmina that have successfully colonised new environments, causing equilibria shifts in native aquatic worlds. At the same time, we dispel some myths about taxa that were misconstrued as invasive in certain localities. Based on our review, the first of its kind for freshwater zooplankton, future environmental monitoring tools including molecular techniques and detailed surveys with rigorous and critical taxonomical assessments may help to provide a clearer picture on the extent of invasiveness of cladocerans. [ABSTRACT FROM AUTHOR]

Elevated lake chloride concentration has been observed in many regions, due to human activities such as mining, agriculture, and urbanisation. Meanwhile, lakes are also experiencing increasing frequency and intensity of heatwaves. The combination of elevated salinity and heatwaves has not been thoroughly studied in freshwater communities, limiting our ability to predict outcomes of future disturbances.We conducted a mesocosm experiment to investigate the individual and interactive effects of increased salinity and heatwaves on a freshwater zooplankton community. The combined effects of the two stressors were examined in two scenarios: when they occurred simultaneously and when a heatwave was preceded by an 8‐week increase in salinity. We expected to see a synergistic effect when the two stressors were applied simultaneously, as organisms might experience energy deficiency due to physiological changes caused by salinity stress and be overwhelmed by the heat treatment. When the two stressors were applied sequentially, we expected them to act independently as the two stressors trigger different physiological responses and physiological homeostasis may have already recovered from previous salt exposure and not influence an organism's response to a subsequent stressor.Individually, increased salinity and heatwave conditions both impaired zooplankton communities with largest effects on copepod nauplii and cladocerans. Together, these stressors caused antagonistic effects on total zooplankton abundance and biomass in both the simultaneous and sequential scenarios, with the combined effects being similar to the salt‐only effects.Our experiment illustrates the potential for heatwaves to have hidden effects when they occur in lakes experiencing salinisation. The findings suggested that the two stressors negatively impacted some zooplankton taxonomic groups, and at the community level, they acted antagonistically such that the occurrence of a 3‐day heatwave did not cause any additional loss of abundance or biomass regardless of whether the community was exposed to the sequential or simultaneous scenario. Our findings also illustrated that even when the two stressors were decoupled in time, the community could still be influenced by a previous stressor. [ABSTRACT FROM AUTHOR]

In an aquatic habitat, zooplankton organisms are an extremely valuable resource for aquaculture purposes. Potential zooplankton species (Ceriodaphnia cornuta) have been further explored to evaluate their applicability to fed fish larvae in freshwater aquaculture. There is a need to find more options other than Artemia as live food options in freshwater hatcheries. Thus, this study was conducted by enriching Ceriodaphnia cornuta with rice bran (F1), soybean meal (F2), Chlorella vulgaris (F3), Spirulina sp. (F4), and unenriched C. cornuta (control). The result showed that the best growth performance of C. cornuta occurred when enriched with an F1 and F2 compared to F3 and F4. Meanwhile, the best initial age of reproduction occurred when enriched with F1+F3 and F3+F4 (3.67 ± 0.57 days and 3.66 ± 1.15 days). Besides, the gross and net reproduction rate of C. cornuta differed with other enrichments where F1+F3 has the highest rates (67.66 ± 1.52 offspring/female and 56.32 ± 0.90 offspring/female) compared to other treatments. The generation time for C. cornuta was shorter when enriched with F2 (7.11 ± 0.88 days) and longer when enriched with F1+F3 (11.23 ± 0.66 days). Other than that, the best growth performance of P. nasutus larvae occurs when fed with F1+F3. This study indicates that F1+F3 constitutes better sources of enrichment to improve the growth performance and life history of zooplankton. [ABSTRACT FROM AUTHOR]

In freshwater ecosystems, the efficiency of transfer of essential substances from phytoplankton to zooplankton, measured as the ratio of the production of these substances in zooplankton to their production in phytoplankton, determines the functioning of higher trophic levels. In addition to carbon, primary producers transfer essential substances, including polyunsaturated fatty acids (PUFAs), nitrogen (N), and phosphorus (P), up the trophic chain. The transfer efficiency of these substances significantly varies in nature depending on environmental factors, which is reflected in the quality of biological resources. The purpose of this review is to analyze the mechanisms regulating the efficiency of the transfer of essential substances from phytoplankton to zooplankton and establish the main factors that may influence the efficiency of their transfer. [ABSTRACT FROM AUTHOR]

Chemical crop protection agents are widely applied in modern agricultural practice. As a result of surface runoff, these insecticides penetrate into rivers, ponds, and lakes, where they become a serious threat to aquatic organisms. The aim of the study was to determine the toxicity of increasing concentrations of the insecticide Decis® 2.5 EC to Daphnia magna and Heterocypris incongruens, which are components of freshwater zooplankton. The observed effect was immobilization of organisms, which were not able to swim after gentle agitation of the liquid for 15 sec. It was found that up to 135 min, increasing Decis® 2.5 EC concentrations inhibited the swimming of tested organisms. Initially, up to 135 min, Heterocypris incongruens was more sensitive to the tested insecticide. After 135 min of the experiment, ostracods acclimatized to the tested xenobiotic. However, after 360 min, the immobilization of organisms increased proportionally to the concentrations of Decis® 2.5 EC. The most toxic concentrations were 15 × 10−3% and 30 × 10−3%. The lowest observed effect concentration of Decis® 2.5 EC that reduced the swimming of daphnia and ostracod by more than 20% was >0.91 × 10−3% (0.23 mg L−1 of deltamethrin). This experiment demonstrated that Daphnia magna and Heterocypris incongruens are good bioindicators of freshwaters polluted with Decis® 2.5 EC. [ABSTRACT FROM AUTHOR]

Thermal plasticity is expected to affect the responses of freshwater zooplankton to climate perturbations. We tested the hypothesis of thermal plasticity in the rigid setae of the second limb of Daphnia galeata. We also aimed to test the role of allometry and the ability to induce a rapid plastic response within an individual lifetime (i.e. postnatal). In all, 300 specimens of Daphnia were dissected from four sets of clonal thermal transfers and seasonal variants from nature. Specimens of D. galeata were cultured under identical conditions save temperature (10 and 20°C). Clonal neonates were reciprocally transferred across temperature regimes to determine the degree of postnatal plasticity. Setae length ratios supported thermal plasticity of rigid seta 2, but a thermal effect was not significant for the length ratios of the soft setae. Simple linear regressions of body length (mm) and setae lengths (mm) under warm and cold conditions revealed significant slope differences (i.e. allometry) among temperatures for the three setae examined. The rigid seta had the largest thermal effect size (slope difference), growing larger at colder conditions for a given body size compared to the soft seta. Rapid thermal plasticity in non-filtering limbs is more important than previously appreciated for Daphnia. [ABSTRACT FROM AUTHOR]

Abstract—Information on the functional traits of the most widespread species of freshwater zooplankton (Rotifera, Cladocera, and Copepoda) in European Russia was collected and analyzed. Our database includes 355 species described by four traits, namely, the maximum body length, trophic group, feeding type, and movement type. Cluster analysis based on Gower's functional distances shows that freshwater zooplankton can be classified into 19 groups with different ecological roles. The characteristics of each functional group identified are presented. We believe it to be fundamentally important to build a unified classification using all available data and traits applicable to all three main taxonomic groups of zooplankton. Comparison with the existing ecological zooplankton classification proposed by Yu.S. Chuikov has demonstrated a number of advantages of our approach. Several ecological groups in Chuikov's classification are represented by more fractional categories in our classification. Our system of functional groups can be used in studies of the structure of zooplankton communities based on direct cluster analysis and ordination or based on functional distances between samples. To calculate the functional similarity between species, one can use our database of traits, which is contained in the Appendix. Analysis based on functional groups gives a better understanding of the community structure than conventional ordination, which takes into account only the taxonomic affiliation of species. The approach used for functional group identification can be useful in assessing the functional diversity and identifying patterns in the dynamics of freshwater zooplankton communities. The database of functional traits of zooplankton can be used to check the relationship of functional traits with environmental variables. [ABSTRACT FROM AUTHOR]

This review provides a Canadian perspective on freshwater zooplankton diversity and ecology across scales and systems. It aims at describing how zooplankton are diverse in forms and functions, and constitute a key component of plankton food webs, a model for ecological theories and a sentinel for monitoring ecological integrity and function in lakes facing environmental changes and anthropogenic stressors. These objectives are addressed across a continuum of scales (continental, regional and local) and systems (reservoirs, lakes and ponds). This perspective shows that the environmental control of zooplankton biodiversity, community structure and function in Canada is complex and variable. Zooplankton communities demonstrated a wide range of responses to anthropogenic disturbances across scales and systems due to interactions with watershed biogeochemistry and climate. This review supports the Multiple Forces hypothesis where forcing by abiotic factors (climate, nutrients, morphometry and chemistry) has a fundamental role at continental scale over Canadian ecoregions, and at regional scale in the Boreal ecozones. In contrast, forcing by biotic factors (algal resources and predators) is relatively more influential at local scale, in resort and urban regions. The challenge for future research will be to combine all new concepts and approaches in a global perspective to better understand the responses of freshwater zooplankton to multiple environmental changes and anthropogenic stressors in Canada. [ABSTRACT FROM AUTHOR]

The association with microbes in plants and animals is known to be beneficial for host's survival and fitness, but the generality of the effect of the microbiome is still debated. For some animals, similarities in microbiome composition reflect taxonomic relatedness of the hosts, a pattern termed phylosymbiosis. The mechanisms behind the pattern could be due to co‐evolution and/or to correlated ecological constraints. General conclusions are hampered by the fact that available knowledge is highly dominated by microbiomes from model species. Here, we addressed the issue of the generality of phylosymbiosis by analysing the species‐specificity of microbiomes across different species of freshwater zooplankton, including rotifers, cladocerans, and copepods, coupling field surveys and experimental manipulations. We found that no signal of phylosymbiosis was present, and that the proportion of "core" microbial taxa, stable and consistent within each species, was very low. Changes in food and temperature under laboratory experimental settings revealed that the microbiome of freshwater zooplankton is highly flexible and can be influenced by the external environment. Thus, the role of co‐evolution, strict association, and interaction with microbes within the holobiont concept highlighted for vertebrates, corals, sponges, and other animals does not seem to be supported for all animals, at least not for freshwater zooplankton. Zooplankton floats in the environment where both food and bacteria that can provide help in digesting such food are available. In addition, there is probably redundancy for beneficial bacterial functions in the environment, not allowing a strict host‐microbiome association to originate and persist. [ABSTRACT FROM AUTHOR]

Theory predicts that population genetic structure and metacommunity structure are linked by the common processes of drift and migration, but how population genetic structure and metacommunity structure are related in nature is still unknown. Deeper understanding of the processes influencing both genetic and community diversity is vital for better predicting how environmental change will impact biodiversity patterns. We examined how crustacean zooplankton and rotifer species' metapopulation genetic structure and metacommunities respond to environmental and spatial variation both within and across four regions of boreal Canada. Metapopulation and metacommunity variation partitioning results were compared within and across the four regions. Metapopulations and metacommunities responded differently to environmental variation and spatial structure both within and across regions, as metapopulations were influenced by different environmental variables compared to metacommunities. At larger spatial scales both metapopulations and metacommunities exhibited greater spatial and environmental structuring, again responding to a different subset of environmental variables. Our findings suggest that even though both genetic and species diversity are linked by the same processes, regional variation in environmental characteristics and spatial structure influence resulting biodiversity patterns differently. To date, no other empirical research has explored relationships between entire metapopulation and metacommunity assemblages at large regional spatial scales. [ABSTRACT FROM AUTHOR]

Concerns about possible environmental implications of nano- and micro-plastics are continuously raising. Hence, comprehensive understanding of their behaviour, bioaccumulation and toxicity potential is required. Nevertheless, systematic studies on their fate and possible effects in freshwaters, as well as the influence of particle-specific and environmental factors on their behaviour and impacts are still missing. The aims of the present study are thus two-fold: (i) to examine the role of the surface charge on nanoplastic stability and acute effects to freshwater zooplankton; (ii) to decipher the influence of the refractory natural organic matter (NOM) on the nanoplastic fate and effects. Amidine and carboxyl-stabilized polystyrene (PS) spheres of 200 nm diameter characterized by opposite primary surface charges and neutral buoyancy were selected as model nanoplastics. The results demonstrated that the surface functionalization of the polystyrene nanoplastics controls their aggregation behaviour. Alginate or Suwannee River humic acid (SRHA) modified significantly the surface charge of positively-charged amidine PS nanoplastic and the aggregation state, while had no significant influence on the negatively-charged carboxyl PS nanoplastic. Both amidine and carboxyl PS nanoplastics were ingested by the zooplankton and concentrated mainly in the gut of water flea Daphnia magna and larvae Thamnocephalus platyurus , and the stomach of rotifer Brachionus calyciflorus. Amidine PS nanoplastic was more toxic than carboxyl one. The toxicity decreased in the order D. magna (48 h -immobilization) > B. calyciflorus (24 h - lethality) > T. platyurus (24 h - lethality). Alginate or SRHA reduced significantly the toxicity of both amidine and carboxyl PS nanoplastics to the studied zooplankton representatives. The implications of this laboratory study findings to natural environment were discussed. Image 1 • Surface functionalization and charge control nanosphere stability. • Amidine PS nanospheres are more toxic than carboxyl one. • Alginate and humic acid formed eco-corona on amidine PS nanospheres. • Eco-corona modulated the surface charge and reduced toxicity to zooplankton. Natural organic matter affects the surface charge of model nanoplastics and decreases their toxicity to zooplankton in a way dependent on the nanoplastic primary functionalization. [ABSTRACT FROM AUTHOR]

Understanding interannual variation of zooplankton communities is a mean for assessment and monitoring of aquatic ecosystems. For this reason, we monitored the zooplankton community of the Sfax saltern (Tunisia) during four years (2000–2003). A multivariate method, the “STATICO analysis” was used to investigate the effect of environmental parameters on the abundance, distribution and composition of the zooplankton community according to time, in three ponds with different salinity values. The results revealed some seasonal and interannual variations of the zooplankton community. Copepods, which were the most abundant zooplankton species, were clearly influenced by the nutrient content variation (higher in spring and autumn) and the anthropogenic pollution level in each pond but their distribution was mainly related to salinity changes. In autumn, Oithona nana (Cyclopoida) proliferated in the least salty pond, Microsetella sp. (Harpacticoida) was abundant at intermediate salinity; and Harpacticus littoralis and Bryocamptus sp. (Harpacticoida) proliferated in the saltiest pond. [ABSTRACT FROM AUTHOR]

A review was carried out on the freshwater zooplankton in Brazil, between 1900 and 2021, based on 1014 studies, and the main trends were pointed. There was an increase of studies from the 1990 s onwards, especially between 2016 and 2020. Most of them addressed ecological research, followed by taxonomical research in the past (mid-1970 s). Field studies were also more numerous than experimental and review ones, but the latter type also increased between 2016 and 2020. Most studies were developed in limnetic regions and in artificial and natural lakes, in contrast to littoral regions, streams and wetlands. Studies on cladocerans were the most numerous in all environments, followed by Copepoda and Rotifera. Protozooplankton was the least studied group, with a predominance of testate amoebae, followed by ciliates, flagellates and naked amoeba studies. We also discuss some aspects of the ecological traits, such as life cycles and life history, population and community dynamics, interactions with the environment, influence of environmental and anthropogenic factors and interspecific interactions. Studies on populations biomass, secondary production, functional ecology, long term duration and molecular analyzes were the main gaps and the next challenges. Finally, it is also necessary to understand the diversity and related variables in different environments that have few or never been studied. [ABSTRACT FROM AUTHOR]

Venezuela has a high diversity of freshwater habitats distributed in seven hydrographic basins. The great variety of conditions that influence them has allowed the development of extensive zooplankton assemblages and a high diversity of taxa. More than 400 zooplankton taxa have been taxonomically recognized within the groups of protozoa, rotifers (the most diverse), cladocerans, copepods, and ostracods. The ecological aspects of zooplankton have received relative great attention. The zooplankton dynamics have been mainly addressed through direct observation in the field and only a few of experimental studies. The presence of invasive species has also been documented. In general, it is considered that more research in specific areas should be encouraged to help improve the knowledge obtained. Efforts should be directed, mainly, to provide incentives that may increase the number of researchers dedicated to the study of freshwater zooplankton, to the establishment of standardized protocols for the application of modern methods of recognition of the species and analysis of ecological processes, effects of global climatic changes and local stressors to zooplankton and the realization of studies on biodiversity in high altitude regions and in particular, different types of aquatic locations with difficult access. [ABSTRACT FROM AUTHOR]

Argentina, an extensive country located in southern South America, encompasses a considerable range of latitude and altitude, with a high diversity of lowland and highland waterbodies. Our study is aimed at providing information regarding the current taxonomic diversity of the main groups of the country's inland-water zooplankton. A total of 242 Protozoa, 375 Rotifera Monogononta, 170 Cladocera, and 120 Copepoda species and subspecies are reported. We submit considerations of the current level of taxonomic knowledge, the regional distribution of the species, and the biogeographical (or zoogeographical) aspects. Since most research was focused on a few regions or a small number of water bodies within large regions, many habitats have been scarcely studied, particularly in areas with wide seasonal or interannual variability. We assume that the potential species number in all groups is much higher than currently recognized. Further studies at wider spatial and temporal scales and at a higher taxonomical resolution as well, are needed in order to provide a full picture of the zooplankton diversity of Argentina. [ABSTRACT FROM AUTHOR]

Diversity of zooplankton in the Bhusara maun was studied during March 2010- Feb 2011. The population of zooplankton consisted of rotifers copepods and cladocerans. Total number of zooplankton recorded were 2335 per litre of which rotifers were 1461 (62.56%), cladocerans 226 (9.67%) and copepods 608 (27.75%). All the dominant groups of zooplankton present throughout the year. Diversity analysis showed that rotifers had 11 species cladoccrans four and copepode four species. High number of zooplankton were recorded in winter season. While low number was recorded in monsoon season. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are becoming saltier due to human activities. The effects of increased salinity can lead to cascading trophic interactions, affecting ecosystem functioning and energy transfer, through changes in community and size structure. These effects can be modulated by other environmental factors, such as nutrients. For example, communities developed under eutrophic conditions could be less sensitive to salinization due to cross-tolerance mechanisms. In this study, we used a mesocosm approach to assess the effects of a salinization gradient on the zooplankton community composition and size structure under eutrophic conditions and the cascading effects on algal communities. Our results showed that zooplankton biomass, size diversity and mean body size decreased with increased chloride concentration induced by salt addition. This change in the zooplankton community did not have cascading effects on phytoplankton. The phytoplankton biomass decreased after the chloride concentration threshold of 500 mg L−1 was reached, most likely due to direct toxic effects on the osmotic regulation and nutrient uptake processes of certain algae rather than as a response to community turnover or top-down control. Our study can help to put in place mitigation strategies for salinization and eutrophication, which often co-occur in freshwater ecosystems. [Display omitted] • Freshwater salinization is a global phenomenon, often co-occurring with eutrophication. • We tested salinization effects on zooplankton community at eutrophic conditions. • High salinity reduced zooplankton biomass and size metrics. • Salinity effects on zooplankton did not have cascading effects on phytoplankton. [ABSTRACT FROM AUTHOR]

Diet quality is crucial for the development of offspring. Here, we examined how the nutritional quality of prey affects somatic growth and the lipid, carbohydrate, protein, amino acid, and polyunsaturated fatty acid content of rainbow trout (Oncorhynchus mykiss) fry using a three-trophic-level experimental setup. Diets differed especially in their content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are physiologically essential polyunsaturated fatty acids for a fish fry. Trout were fed with an artificial diet (fish feed, DHA-rich), marine zooplankton diet (krill/Mysis, DHA-rich), or freshwater zooplankton diet (Daphnia, Cladocera, DHA-deficient). The Daphnia were grown either on a poor, intermediate, or high-quality algal/microbial diet simulating potential changes in the nutritional prey quality (EPA-content). Trout fed with the fish feed or marine zooplankton entirely replaced their muscle tissue composition with compounds of dietary origin. In contrast, fish tissue renewal was only partial in fish fed any Daphnia diet. Furthermore, fish grew five times faster on marine zooplankton than on any of the Daphnia diets. This was mainly explained by the higher dietary contents of arachidonic acid (ARA), EPA, and DHA, but also by the higher content of some amino acids in the marine zooplankton than in the Daphnia diets. Moreover, fatty acid-specific carbon isotopes revealed that trout fry could not biosynthesize ARA, EPA, or DHA efficiently from their precursors. Our results suggest that changes in the zooplankton and macroinvertebrate communities' structure in freshwater habitats from DHA-rich to DHA-poor species may reduce the somatic growth of fish fry. [Display omitted] • We simulated lowered nutritional quality of prey to the development of rainbow trout fry. • Trout were fed with DHA-rich (fish feed or marine zooplankton) and DHA-deficient (freshwater Daphnia) diets. • Lowered nutritional quality of prey suppressed growth of fish fry. • Fish fry was unable to overcome lowered availability of long chain polyunsaturated fatty acids. [ABSTRACT FROM AUTHOR]

1. The model of the International Society of Limnology (SIL) Plankton Ecology working group (hereafter the PEG model) is a verbal model describing the patterns and driving factors of seasonal phytoplankton and zooplankton succession in oligotrophic and eutrophic lakes (Sommer et al., 1986). Despite being a citation classic, tests of the PEG model with respect to differences in zooplankton biomass dynamics between oligotrophic and eutrophic lakes are lacking. 2. Here, I use the long-term data from Lake Constance, which during the last 100 year changed from an (ultra-) oligotrophic lake to a eutrophic lake and back to an oligotrophic lake to analyse trophic status differences in zooplankton biomass seasonality. Using data from one lake allows one to study trophic influences on biomass dynamics without the confounding effects of lake geographical setting and lake morphology, which complicate comparative dynamics in eutrophic versus oligotrophic lakes. However, environmental changes due to other driving factors, for example climate change, may possibly alter biomass dynamics as well. 3. Data from Lake Constance do not support the differences in zooplankton seasonality in respect to peak timing between eutrophic and oligotrophic lakes suggested by the PEG model. Rather total zooplankton biomass, as well as cladoceran and copepod biomass showed a peak in May/June during all trophic conditions. Biomass dynamics of cladocerans during spring were more strongly influenced by water temperature than by trophic state. Furthermore, analyses of the geographical setting of the lakes considered in Sommer et al. (1986) suggest that the proposed differences in zooplankton seasonality between eutrophic and oligotrophic lakes are at least partially due to the confounding effect of lake altitudinal setting; the oligotrophic lakes were located at higher altitude than the eutrophic lakes. 4. As a consequence of the results from Lake Constance, and the bias detected in the Sommer et al. (1986) study, a modified PEG model is proposed which considers low water temperature and not food limitation as the most important factor reducing zooplankton growth rate during early spring in both oligotrophic and eutrophic lakes. [ABSTRACT FROM AUTHOR]

1. Interactions between multiple anthropogenic stressors can have unexpected synergistic or antagonistic effects, making it difficult to predict their combined effects using single-stressor studies. The interaction between invasive consumers and nutrient enrichment is particularly important as both stressors frequently co-occur, and their respective bottom-up and top-down effects have the potential to interact across multiple trophic levels. 2. We conducted a mesocosm experiment that crossed an increasing nutrient addition gradient against an increasing zebra mussel invasion gradient. Native zooplankton communities were added to the mesocosms, and after 3 months, we examined how the single-stressor effects on available resources and the zooplankton community were altered by their multiple-stressor interaction. 3. Added nutrients had no effect on small phytoplankton, but increased the abundance and dominance of copepods and reduced the density of large phytoplankton, probably due to increased topdown predation pressure. Zebra mussels reduced large phytoplankton concentration by about 80%, rotifer abundance by about 75%, and shifted communities towards dominance by cladocerans and adult/juvenile copepods. 4. When combined, the top-down control exerted by the mussels interacted antagonistically to prevent any bottom-up influence of nutrient enrichment on the zooplankton community. These results provide insight into the potential outcomes of nutrient and invasive consumer stressor interactions, and illustrate the need for researchers to consider environmental change in a multiple-stressor context. [ABSTRACT FROM AUTHOR]

Changes in the functional groups of zooplankton were studied in autumn in a temperate floodplain lake (Lake Sakadaš, Kopački Rit Nature Park, Croatia) and in the Drava River (in the Croatian part of the river). Various abiotic parameters as well as available food sources (phytoplankton and microphytes (algae and cyanobacteria) developing on epixylon, epilithon and artificially introduced microplastics called "plastisphere") were also studied. The lake was hydrologically isolated from the main river during the study, while the water level of the Drava River fluctuated, resulting in larger variations in limnological parameters. Due to stable conditions in the lake, zooplankton abundance, biomass, and species richness were higher than in the Drava River. In both environments, zooplankton species feeding on bacteria, detrital suspensions, and small algae were most abundant, with predators and microfilter-feeders being more abundant in the lake. Microphytes were diverse and mostly small and medium-sized in phytoplankton and all substrate types. Stable lake conditions promoted higher abundance of the zooplankton group, which effectively uses larger algae as a food source. The lower abundance of zooplankton feeding on larger algae and predatory species in the river suggests that the epilithon and plastisphere community was a less mature community compared to the lake, and the heterotrophic component with ciliates and/or other small heterotrophs was not well developed. The importance of plastispheres was particularly evident under the turbid hydrologic conditions that prevailed in the river at the end of the study, when phytoplankton biomass decreased and zooplankton abundance steadily increased, suggesting that microphytes colonised on microplastics were an additional food source for higher trophic levels. [ABSTRACT FROM AUTHOR]

Species distribution models (SDM's) are powerful tools used to describe species suitable habitats and spatial occurrences and many statistical methods and algorithms are available to model the spatial distribution of a target species. Here we explore a species distribution model framework combined with machine learning algorithms to describe the distribution of two freshwater zooplankton species Daphnia longispina (Cladocera) and Eucyclops serrulatus (Copepods) in a system of 283 shallow and ephemeral freshwater habitats in the Northern Italian Appennines. For each species, we model the habitat suitability by comparing one regression-based model, one generalized linear model (GLM) and two machine learning algorithms: random forest (RF) and artificial neural network (ANN) with one hidden layer. We used a total of 27 predictor variables. The modeling framework was used considering a scenario of future climate change in order to evaluate potential shifts in spatial distribution of the zooplankton species. For both species, the supervised machine learning algorthn (ANN) produced the highest mean values for all the performance metrics. For D. longispina and E. serrulatus , the two most important variables ranked by the shap analysis and global sensitivity and uncertainty analysis (GSUA) were temperature seasonality and precipitation of the warmest quarter. Both species, in a future climatic change scenario, are expected to shift their distribution mainly toward lower northern altitudes with an overall expansion of 7% with respect to the past/present climatic conditions. However, the spatial expansion of D. longispina and E. serrulatus was qualitatively different. In agricultural and natural areas, the expansion of E. serrulatus was greater than that of D. longispina but, in natural areas, the expansion of E. serrulatus was counterbalanced by a greater spatial contraction than that of D. longispina. As hypothesized, direct and indirect anthropogenic pressures may affect the predicted potential shift and expansion of the zooplankton species. [Display omitted] • We used ML to model the past and future distribution of two zooplankton species. • Artificial neural networks outcompete random forest and generalized linear model. • The spatial expansion of D. longispina and Eucyclops serrulatus was different. • Anthropogenic pressures may affect the potential shift of the zooplankton species. [ABSTRACT FROM AUTHOR]

We examined if the results of statistical analyses of the relationship between copepod communities and water masses would be affected by the mesh size of the plankton net, by comparing abundance and species composition of copepods in plankton samples collected by plankton nets of different mesh sizes. Our samples were collected during the summer of 2006 in the East China Sea (ECS) by plankton nets with mesh sizes of 100 and 330 μm. The abundance of copepods collected by the 100 μm-mesh plankton net was about two orders of magnitude higher than that collected by the 330 μm-mesh plankton net. The difference in abundance was mainly due to the loss of small-sized copepods in the samples collected by the plankton net with the larger mesh. Species richness was higher in samples collected by the 100 μm-mesh net and Piélou's evenness was generally higher in samples collected by the 330 μm-mesh net. Although species composition of copepods varied in samples collected by plankton nets with different mesh sizes, the statistical analysis of the relationship between the copepod community and the water masses in these samples appeared not to be affected. [ABSTRACT FROM AUTHOR]

Oncorhynchus nerka occur both as anadromous sockeye salmon that spend most of their life in the ocean, and as non-anadromous kokanee salmon that remain in fresh water their entire lives. We assessed whether stable isotopes of sulfur (δS) in otoliths could be used to distinguish sockeye salmon and kokanee ecotypes that are otherwise difficult to identify when they share a common freshwater rearing environment. We also investigated the chemical link between salmon and their diet by measuring δS in various fish tissues (eggs, muscle, scales) and zooplankton. δS (mean±SE) in sockeye salmon eggs (18.7 ± 0.4‰) and marine zooplankton (20.5 ± 0.1‰) were enriched by 10-14‰ compared with kokanee eggs and freshwater zooplankton. δS in the otolith cores of sockeye salmon (19.2 ± 0.7‰) and kokanee salmon (5.3 ± 1.1‰) were similar to δS in marine and freshwater zooplankton, respectively, indicating that the core is derived from maternal yolk tissue and reflects the maternal diet. δS in the freshwater growth zone of otoliths did not differ significantly between sockeye (5.9 ± 1.1‰) and kokanee salmon (4.4 ± 1.2‰), and was similar to freshwater zooplankton. The mean difference between δS in the otolith core and first year of growth was 13.3 ± 1.4‰ for sockeye and 0.65 ± 1.3‰ for kokanee salmon. A quadratic discriminant function developed from measurements of δS in otoliths of known maternal origin provided perfect classification rates in cross-validation tests. Thus, sulfur isotope ratios in otoliths are effective in discriminating between anadromous and non-anadromous ecotypes of O. nerka. [ABSTRACT FROM AUTHOR]

I conducted a three-season study on three lakes in three different habitats (Chara tomentosa bed, Typha angustifolia stand, and the open water) in order to determine the best predictors of microcrustacean distribution. The seasonal composition and abundance of crustacean zooplankters were typical of the pelagic zone in temperate lakes, and there was no appreciable difference in the zooplankton communities among the lakes. The lowest species richness and total abundance were in the open water zone, while the highest richness and abundance were within the C. tomentosa stand. Moreover, two cladoceran species (Acroperus harpae and Chydorus sphaericus) were uniquely associated with C. tomentosa. Canonical correspondence analysis identified density of plant stems and oxygen and total organic carbon concentrations in the water as the most important factors structuring the distribution of the microcrustacean community. Stepwise multiple forward regression confirmed that plant stem length and biomass were biometric parameters that influenced crustacean density. Total nitrogen concentration and pH were implicated in the density of Ceriodaphnia puichella, while temperature and conductivity influenced A. harpae abundance. [ABSTRACT FROM AUTHOR]

Zooplankton produce resting eggs and diapause stages as strategies to promote their survival during periods of adverse environmental conditions, thereby ensuring the community diversity. The goal of this study is to investigate the contribution of these eggs, which were present in the sediment of an isolated lagoon in the Upper Paraná River floodplain, to cladoceran diversity. The species hatching from the resting eggs in the sediment do not occur in the plankton. Sediment samples were collected at six sampling sites in the Osmar Lagoon banks, in September 2004 and June, July, August and September 2005. Zooplankton were sampled in the pelagic region, using a motorized pump (1000 L) and plankton net (68 µm). The pH, water temperature (°C), electrical conductivity (µS cm−1) and dissolved oxygen concentration (mg L−1) also were measured. The resting eggs were counted in the laboratory, being maintained under constant temperature and photoperiod until their analyses. The resting eggs were examined daily until hatching. A higher abundance of these eggs was observed in July, during a period of lower temperature and electrical conductivity, and higher pH and dissolved oxygen concentrations. ANOVA results indicated significant differences in resting egg abundance among the sampling months. Ceriodaphnia reticulata, Macrothrix spinosa, Ilyocryptus spinifer, Ephemeroporus tridentatus and Diaphanosoma sp. hatched from the resting eggs, although they were not observed in the plankton samples. C. reticulata was observed for the first time in this floodplain, with these study results corroborating the hypothesis that resting cladoceran eggs do contribute to zooplankton diversity in the lagoon. [ABSTRACT FROM AUTHOR]

We studied diel vertical migration (DVM) of a variety of zooplanktonic taxa. Our results fit the predictions of the predator avoidance hypothesis, with larger taxa performing normal migrations to avoid fish predation and smaller taxa performing reversed migrations, probably to avoid predation by Chaoborus. Cladocerans and adults of copepods displayed normal DVM, whereas cyclopoid copepodites did not migrate. Five rotifer taxa migrated in a normal pattern whereas four taxa migrated in a reverse pattern. Our results suggest that during the day microcrustaceans moved close to the bottom, while rotifers showed narrower migration amplitudes. Larvae of the invertebrate predator Chaoborus displayed strong normal DVM, and appeared to synchronize its life cycle with the lunar cycle, with mass emergence of adults around New Moon. [ABSTRACT FROM AUTHOR]

Virtually all species of Hyperiidea have a symbiotic relationship with gelatinous zooplankton. It has been theorized that hyperiid amphipods are descendants of benthic crustaceans that have developed a unique benthic-like existence on the pelagic substratum provided by gelatinous zooplankton. But does this strategy have hidden metabolic costs? Metabolism, in the form of both direct respiration and enzyme activities, and proximate composition of Phronima were compared to pelagic and benthic crustaceans. Although less energy is needed to remain in the water column since the gelatinous zooplankton makes the Phronima more buoyant than just Phronima alone, metabolicrates of Phronima are not lower than those of other pelagic crustaceans, possibly due to the energy needed to propel the barrel. However, Phronima have lower protein concentrations, indicating less energy is allocated to muscle production. The ratio of LDH (L-lactate dehydrogenase) activity to CS (citrate synthase) activity was >1, indicating that burst swimming is important in Phronima's metabolism. The symbiotic relationship provides the Phronima with food and a substrate for the brooding of young, but does not give them an energetic advantage over other pelagic crustaceans. [ABSTRACT FROM AUTHOR]

1. The spatial distribution and movement patterns of zooplankton in large rivers are little known compared with those in lake environments. We conducted a series of studies in the Ohio River (U.S.A.) during the low flow period to assess diel vertical (DVM), longitudinal and lateral movement of crustacean zooplankton. 2. The dominant large zooplankter, the copepod Eurytemora affinis, showed a consistent vertical migration pattern of daytime ascent and night-time descent during all sampling periods – the reverse of the most common migratory pattern of zooplankton in lakes. The cladoceran Bosmina migrated in a similar way in two of the three sampling periods. Surveys taken longitudinally in the river showed similar trends for both taxa. 3. During the lateral surveys, E. affinis was significantly more abundant in the shallow littoral zone during the night than in the daytime. The combination of vertical and lateral movement patterns along with the diel distribution of zooplanktivorous fish suggest that these movements are a predator-avoidance mechanism. 4. Sampling programmes in large rivers should consider that larger zooplankton such as E. affinis may not be randomly distributed in the river channel and behaviours such as diel vertical migration may be just as evident in river habitats as in lakes. [ABSTRACT FROM AUTHOR]

Shallow lakes can occur in two alternative stable states, a clear-water state and a turbid state. This is associated with separate assemblages of fish, zooplankton and plants. Little is known about whether macroinvertebrate assemblages differ across both stable states. This study investigated this in a connected set of three turbid and three clear-water shallow lakes. To overcome confounding effects of differences in spatial structure of macrophytes in turbid and clear-water lakes, we sampled three microhabitats that occurred in both alternative stable states: open water, sago pondweed (Potamogeton pectinatus) and reed (Phragmites australis). Univariate analyses indicated no differences in the number of organisms, taxon richness or diversity between turbid and clear-water lakes. Multivariate analysis, however, showed significant differences in the macroinvertebrate community structure of both stable states. Nine taxa explained a significant amount of the variation between both lake types, of which seven preferred the clear-water lakes. The number of organisms and the taxon richness were higher in reed than in the other microhabitats, but diversity and evenness did not differ among the microhabitats. Multivariate analyses could separate all three microhabitats. Eight taxa, mainly detritus feeders and collector-gatherers, explained most of the variation in the data and preferred the reed microhabitat. The effects of stable state (6.8% explained variance) and microhabitat (13.1% explained variance) on the macroinvertebrate assemblages were largely independent from each other (1.5% shared variance). Although macroinvertebrates are not implemented in the initial theory of stable states, our results show clearly different assemblages across both stable states. [ABSTRACT FROM AUTHOR]

Aggregate stages of the salps Thalia democratica, Cyclosalpa affinis and Salpa cylindrica collected by SCUBA diving in the Mid-Atlantic Bight were fed with naturally occurring food assemblages. This is one of the few studies where salps have been fed with natural food assemblages. The estimated clearance rate for all species based on disappearance of chlorophyll varied from 82 to 444 mL individual−1 day−1. Cell counts showed that T. democratica mostly ingested carbon from autotrophic nanoflagellates and autotrophic dinoflagellates. Ingestion by S. cylindrica was primarily on larger prey, such as dinoflagellates, while C. affinis ingested auto- and heterotrophic nanoflagellates. All main prey types ingested by salps corresponded to those that contributed most to biomass at each experimental station. Thus, salps fed on naturally occurring particles primarily in proportion to prey biomass and to their mechanical capacity to be retained and ingested. Feeding by salps on dinoflagellates and ciliates implies that they may act not only as potential competitors with microzooplankton, but also as consumers of them. [ABSTRACT FROM AUTHOR]

Mycosporine-like amino acids (MAAs) were studied in zooplankton from 13 Argentinian lakes covering a broad range in altitude, maximum depth and physico-chemical properties of the water. Four to nine different MAAs (predominantly porphyra-334 and shinorine) were found in the copepods Boeckella gibbosa, B. gracilipes, B. meteoris and Parabroteas sarsi, and in the ciliate Stentor amethystinus, while MAAs were undetectable in the cladoceran Daphnia middendorffiana. Among the different copepods, maximum MAA concentrations accounted for 0.25–1.31% of the dry weight, and contents were generally about three to seven times (up to 43 times) higher in the animals living in the clearest lakes compared to those occurring in low-UV systems. This variability in the content of MAAs was related to the lake altitude (r2 = 0.71), and the fraction of the water column to which 1% of the surface UV radiation at 320 nm penetrated (r2 = 0.57). Our data therefore underscore the role of MAAs as sunscreens to decrease the potential negative effects of solar radiation, but they also indicate that other environmental factors besides UV transparency play a role in determining MAA concentrations. One lake was selected to obtain additional information on the qualitative composition of MAAs in seston of <100 μm between two sampling sites and over a 2 month study period (austral summer). Six different MAAs were detected in the samples, with porphyra-334 and palythine being predominant. In the copepods collected simultaneously, there was low variation in MAA concentrations between the two sites and over time. Thus, our results suggest that under similar UV exposure conditions MAA contents of planktonic organisms show low temporal variation. [ABSTRACT FROM AUTHOR]

Predation by fish has commonly been viewed as a primary driver of spatial and seasonal variation in Daphnia dominance and the size structure of zooplankton communities. Yet, previous research suggests that large Daphnia do not always dominate in the absence of predation. As alternatives to the planktivory model, numerous mechanisms have been put forth, including the effect of resource competition and its interaction with resource quantity and quality and abiotic factors (e.g. temperature). Here results are presented of a field survey of 18 fishless, permanent ponds in southwest Michigan in which spatiotemporal variation in Daphnia pulex abundance and several potential determinants of this variation are explored. Results revealed a large amount of variation in D. pulex incidence and relative biomass, with some ponds exhibiting seasonal losses, some having few or no Daphnia, and some being dominated by D. pulex for the entire sample period. Redundancy analysis of zooplankton composition and pond environmental variables (biotic and abiotic) showed no relationship between D. pulex biomass and measures of Chaoborus abundance, algal resource production, or algal resource quality (including seston C:N:P). Instead, pH and temperature (both of which covaried) showed the strongest relationship with D. pulex biomass. [ABSTRACT FROM AUTHOR]

Presents a study that examined anomalously low zooplankton abundance in the Ross Sea. Background on the study area; Materials and methods; Results of the study.

Verifies the assimilation of micro- and mesozooplankton by zebra mussels. Demonstration of the food web link between zooplankton and benthic suspension feeders; Assimilation efficiencies of zebra mussels on rotifer species Brachionus calyciflorus and Lepadella ovalis; Energy budget of zebra mussels when feeding on rotifers.

Presents a study that examined the trophic relationships among Southern Ocean copepods and krill. Some uses and limitations of a stable isotope approach; Experiments with Euphausia superba; Regional and seasonal differences in the stable isotope ratios of particulate organic matter and zooplankton.

Presents a study that examined the control of zooplankton dependence on allochthonous organic carbon in humic and clear-water lakes in northern Sweden. Physical, chemical and biological characteristics of several subarctic lakes in northern Sweden; Model used to compute phytoplankton fractionation as a function of the ratio between the phytoplankton specific growth rate and the lake water carbon dioxide concentration in the lakes; Stable carbon isotopic composition of different components of the lakes.

Presents a study that tested the importance of zooplankton for the persistence of a deep chlorophyll layer. Summer limnological conditions in Yellow Belly Lake, Idaho; Limnocorral characteristics and phytoplankton; Mean limnocorral chlorophyll and temperature.

Presents a study that assessed microzooplankton grazing on Prorocentrum minimum and Karlodinium micrum in Chesapeake Bay. Culture and staining of dinoflagellates; Chesapeake Bay and Potomac River stations during summer 2000 cruises; Surface microzooplankton abundance and distribution.

This review focuses on monospecific swarms of four taxonomic groups of small crustaceans. Three groups are marine copepods: oithonids (Oithona and Dioithona), Acartia species and Calanus species. The fourth group includes freshwater cladoceran species in the Order Anomopoda. Swarming characteristics of each taxonomic group are reviewed, proximal cues for swarming are described, comparisons are made for proposed advantages of swarming, and future research directions are suggested.

The relationships of generation time to both adult body mass and temperature are critical to our understanding of numerous aspects of zooplankton behavior, ecology and evolution, yet these relationships remain poorly understood. Here, I use a meta-analysis to define the relationship of generation time to body mass and temperature for both marine and freshwater zooplankton species (rotifers, copepods and cladocera), for temperatures from 5–20°C. I also define a relationship for the constituent parts of generation time (embryonic and postembryonic development time) as a function of egg and body mass for zooplankton across this temperature range. These relationships provide powerful tools for evaluating differences in generation time between individual zooplankton species. [ABSTRACT FROM PUBLISHER]

1. Boundaries between growth limitation by carbon (C) and phosphorus (P) in homeostatic heterotrophic consumers such as zooplankton will vary as demands on these two elements vary, as they should at different food quantities. At very low food quantity when production is close to zero, metabolic requirements (for carbon) become more important than growth requirements (for carbon and phosphorus in fixed proportion). Thus, the boundary separating C-and P-limited growth should be at a higher C : P ratio at low food quantity than at high food quantity. 2. A model including both metabolism and growth indicates that consumer growth should differ between foods of high vs. low phosphorus concentration only when food quantity is above a certain level. Thus, two foods might give identical consumer growth rates at low food quantity but give different consumer growth at higher quantity. 3. Solution of the model using parameters based on 2 mm Daphnia compared with a survey of C and P in seston of marine and freshwater sites supports earlier conclusions of the potential importance of food quality constraints on Daphnia growth. [ABSTRACT FROM AUTHOR]

1. The effects of Daphnia infochemicals on the morphology and biochemical composition of Scenedesmus were studied and subsequently their influence on Daphnia life history. Three species of Scenedesmus (S. acutus, S. obliquus and S. subspicatus) were tested for Daphnia-induced colony formation. Life history experiments were performed with Daphnia cucullata and D. magna feeding on unicellular or colonial S. acutus. 2. Colony formation was promoted when S. acutus and S. obliquus were exposed to filtered water from a D. magna culture. S. subspicatus did not form colonies when exposed to culture water, but showed some colony formation when exposed to live D. magna. 3. No clear differences were found in total lipid, protein or carbohydrate content between the unicellular and colonial ecomorphs of the three Scenedesmus species. However, fatty acid (FA) concentration and composition were changed. Total FA as a percentage of frozen dry weight (DW) were increased in colonies. The ratio of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) and the ratio of ω3 : ω6 fatty acids decreased in colonies. 4. A short-term grazing experiment with three size classes of Scenedesmus revealed lower clearance rates for small Daphnia when feeding on large colonial Scenedesmus. 5. Life history parameters of both Daphnia species were influenced by food type. The intrinsic rate of population increase (r) was significantly lower for daphnids feeding on colonies. 6. The negative influence of colonial Scenedesmus on population growth of Daphnia seems to be determined by algal morphology rather than biochemical composition. [ABSTRACT FROM AUTHOR]

1. The composition of fatty acids (FA) from C14 to C18 was measured for edible seston and for individual Daphnia galeata, Diaphanosoma brachyurum and Eodiaptomus japonicus from Lake Biwa using a pyrolysis--gas chromatography (Py-GC) method. Based on the relative abundance of the FA, inter-and intraspecific differences in composition were examined. 2. Among the FA, C16 : 0 was the most abundant, both in the three zooplankton species and in edible seston smaller than 20 μm, suggesting that the composition of the zooplankton was roughly reflected by their diet. However, the abundance of C18 : 1 relative to C16 : 1 and C18 : 0 was much higher in each zooplankton species than in the diet. 3. Comparison of the relative abundance of FA among the three zooplankton species revealed that intraspecific differences in FA composition are greater than interspecific differences. These results indicate that variability in FA composition is not necessarily species-specific, and can be obscured by variation in composition between individuals. [ABSTRACT FROM AUTHOR]

This article examines sexual dimorphism in copepods, ciadocerans, and rotifers. All three groups can be commonly found in freshwater and sometimes in the salty water but only the copepods are generally found in marine zooplankton communities. These three groups exhibit important differences between the sexes in size and in other secondary sexual characteristics to varying degrees, that are not directly related to reproduction. The life cycle is summarized for each group. The article then describes genetic, morphological, physiological, and behavioral differences between the sexes, and finally discusses the evolution of these differences and their ecological implications.