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In this study, we have shown that nutrient input in aquatic ecosystems has different impacts on the various facets of phytoplankton and zooplankton diversity. We designed an experiment with eleven levels of nutrient addition replicated four times. Alpha, beta, and gamma taxonomic and functional diversity indices were calculated based on organisms' occurrences and abundances in each microcosm, among microcosms of the same treatment and for the set microcosms of a same treatment. There was an increase in species richness and a decrease in equitability along the gradient for both groups. Taxonomic beta diversity based on occurrences was positively related to nutrient gradient, but a hump-shaped relationship between nutrient enrichment and beta diversity was observed when abundance data were considered, showing greater variation in species composition at intermediate levels of nutrient. Alpha functional richness increased for both groups, whereas alpha and gamma RaoQ, and gamma functional divergence decreased, indicating that nutrient enrichment promotes functional trait richness, but also the dominance of species. At small spatial scale and at a short period of time, we showed that taxonomic and functional diversities respond in similar ways to nutrient enrichment. We conclude that nutrient input may modify community composition and affect ecological processes overtime. [ABSTRACT FROM AUTHOR]

We evaluated temporal trends in zooplankton functional diversity (functional richness—FRic, evenness—FEve divergence—FDiv, and Community-Weighted Means—CWM) in 12 habitats of the Upper Paraná River floodplain (Brazil) over 16 years (2000–2016) and their relationships with environmental predictors (chlorophyll-a, water depth, and turbidity). We hypothesized that different environmental drivers affect zooplankton's functional component in a distinct way. We predicted that: (i) FRic is positively related to increases in chlorophyll-a concentration and turbidity associated with impacts of damming on the floodplain and depth. (ii) FEve is negatively related to increases in chlorophyll-a concentration and turbidity, and positively related to depth. (iii) FDiv is negatively related to the increase in chlorophyll-a, depth, and turbidity. (iv) Finally, we asked how do each of the traits change the functional indexes and their relation to environmental predictors. FRic and FEve fluctuated oppositely and cyclically every five years. FDiv showed a trend similar to that of FRic. However, between 2005 and 2010 FDiv only decreased. All functional diversity indexes were explained by temporal variability, depth, and chlorophyll-a concentration. However, the influence of each variable was different for each component of functional diversity. For CWM, turbidity was negatively associated with life span and positively associated with predator escape, and type of reproduction, while predator escape and feeding type were negatively associated with depth. We highlight that, in order to maintain the drivers of zooplankton functional diversity (food availability, turbidity, and depth), it is extremely important to guarantee the floodplain ecosystem's original state of functionality. [ABSTRACT FROM AUTHOR]

The oligotrophication of freshwater is the reduction of the nutrient concentration in the water column, which causes the depletion of organic matter and diminishes the biological production of the ecosystem. To elucidate the zooplankton response to nutrient depletion (oligotrophication), an experiment was performed in mesocosms simulating real scenarios. Phytoplankton and zooplankton inocula were collected in the Upper Paraná River Floodplain and subjected to combinated nutrient and transparency treatment. We evaluated whether resource limitation and increased transparency (both associated with oligotrophication) affect the size structure of planktonic crustaceans. The effects of predation were corroborated in the treatments with low nutrient concentrations. Thus, the oligotrophic scenario (high transparency and low nutrient concentration) indicated a decreased size structure of zooplankton, probably because of the predation pressure, supporting the predictions of the size-efficiency hypothesis (SEH). When resources were abundant (in treatments with high nutrient concentrations), the decrease in the size structure indicated that the enrichment of nutrients favoured small individuals. Our results showed that nutrient and transparency manipulation affected species richness, the abundance of individuals, and the zooplankton community size structure. Therefore, we suggest that oligotrophication affects predation and competition dynamics in zooplankton. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the effects of nutrient enrichment on primary and secondary productivity, the relationship between these ecosystem processes, and the relationship between the resources of zooplankton community in response to ecosystem processes, experimentally. The experimental design was randomized, with three levels of nutrient replicated three times, giving a total of nine experimental units, for a period of 30 days (November-December, 2013). We measured primary productivity, secondary productivity, and zooplankton community structure, at the beginning and after every seven days of the experiment. Primary and secondary productivity increased with nutrient enrichment. Secondary productivity was supported by a few dominant species with ecologically selected traits, especially large-bodied zooplankton (copepods and large cladocerans). Nutrient enrichment turned the relationship between primary and secondary productivity from positive to negative and intensified the biotic process of competition because of exploitation by zooplankton populations, favoring an increase in the dominance of large microcrustaceans. This reflects the initial effects of a moderate eutrophication. At a larger temporal scale and at higher nutrient concentrations, effects of higher magnitude are expected, which may disrupt the whole community, resulting in the loss of ecosystem processes. [ABSTRACT FROM AUTHOR]

Dams have altered the physiography and ecology of large rivers, causing severe environmental changes at a global scale. Assuming that series of reservoirs induce physical, chemical, and biological longitudinal changes in rivers, we tested the hypotheses that (i) the structure of biological communities in reservoir cascades is not only affected by changes in water quality, but also by cumulative hydrological alteration and impacts on river connectivity; and (ii) fish are more affected by cumulative effects of reservoirs when compared to other aquatic assemblages. Samplings of three assemblages (phytoplankton, benthic macroinvertebrates, and fish) were conducted in the reservoir cascade of São Francisco River, Brazil. We estimated the relative role of environmental and spatial predictors through variation partitioning analyses. Environmental variables, cumulative reservoir volume, longitudinal position, and distances from nearest reservoirs were used as explanatory variables. Environmental variables were the most important for the phytoplankton community. No significant effects of the predictors used were found for benthic macroinvertebrates, whereas spatial variables and cumulative reservoir volume were the most important predictors for fish. Therefore, our results provide evidence of impacts along reservoir cascades, and suggest that their effects mainly influence fish assemblages. [ABSTRACT FROM AUTHOR]

We determined the variation in the composition of plankton communities (zooplankton, phytoplankton, and ciliates) in subtropical lakes at different temporal scales, in relation to the seasons (dry and rainy seasons), as well as at finer (among months) and broader (ENSO—among El Niño, La Niña, and normal climate events) scales. Using a 16-year time-series dataset, we tested the hypothesis that seasonal variation would explain most of the gamma diversity of these plankton communities. We also investigated the environmental and temporal factors responsible for the variations in composition and species turnover. The scale related to dry and rainy seasons explained a considerable percentage of the gamma diversity and variation partitioning, showed that compositional changes occurred mainly over broader temporal scales. Environmental factors varying among seasons and ENSO events explained changes in composition, although some communities did not respond to the environment. Our results suggest that niche and stochastic processes operating at temporal scales correlated with ENSO climate events contributed to changes in species composition. Hence, climate anomalies might be important to maintain diversity in areas with reduced or loss of the natural variations in environmental conditions. Our results also suggest that, although communities show similar patterns of variation in composition, they might respond in a different degree to environmental and temporal factors. Thus, while niche-associated (environment) and stochastic (time) processes drove the phytoplankton, stochastic processes were more important for zooplankton, whereas neither were important for ciliates. [ABSTRACT FROM AUTHOR]