Abstract Temperature rise has effects on the metabolic process of organisms, population structure, and ecosystem functioning. Here, we tested the effects of warming on the metabolic rates and life-history parameters of the widespread cladoceran Ceriodaphnia silvestrii. Two scenarios of global warming were established, an increase of 2 °C and an increase of 4 °C; the control temperature was 22°C. Our results showed that warming altered C. silvestrii metabolic rates, by increasing the rates of assimilation and secondary production, and decreasing the rates of filtration and ingestion. Warming also increased C. silvestrii fecundity and the body size of neonates and juveniles, and decreased the embryonic and post-embryonic time of development. C. silvestrii might be an important food resource at intermediary temperature as it had higher assimilation rates, even filtering fewer algae. At the highest temperature, we observed a substantial decrease in assimilation and secondary production, which could be a sign of stress starting. The increase in temperature by global warming will affect the cladocerans’ metabolic processes and the population survival, even a small increase (2°C) might induce drastic fluctuations in such processes and affect the carbon and energy availability inside aquatic food-webs.

Abstract Environmental heterogeneity influences the physiology and behavior of organisms, leading to alterations in populations, communities, and ecosystems. This study was designed to evaluate the effect of the spatial and temporal limnological heterogeneity on the distribution of copepods in the Amazon River floodplain, Araguaia River floodplain, Pantanal floodplain, and Upper Paraná River floodplain. We performed dispersion homogeneity tests (PERMIDISP) to analyze the limnological heterogeneity, a Generalized Linear Mixed Model (GLMM) to test the relationship between limnological heterogeneity and species distribution, and a Canonical Correspondence Analysis (CCA) to analyze which limnological variables explain the variation in the community composition. In our study, we observed higher environmental heterogeneity during dry periods, especially in the Amazon floodplain. The Amazon showed the highest species richness (the total number of species that occurred in each floodplain), with endemic species, also the highest abundance of individuals, especially during dry periods, which was possibly due to the biogeography, the size of the basin, and the heterogeneity of the environments. The Pantanal presented the second highest species richness and showed the highest species richness and abundance of individuals during rainy periods. The distribution of copepods was highly correlated with environmental heterogeneity. The species were mainly related to temperature, nutrients, and depth.

Abstract Pesticides have reached aquatic ecosystems and have caused numerous impacts on organisms. The present study aimed to assess the sensitivity of Daphnia similis Straus 1820 and Pseudokirchneriella subcapitata (Korshikov) F.Hindák to three commercial pesticides with different active ingredients: Siptran 500SC® (atrazine), Dimilin® (diflubenzuron), and Aproach Prima® (picoxystrobin + cyproconazole). For this purpose, we performed acute toxicity tests on these organisms. The compound most toxic to D. similis was the insecticide Dimilin® (toxic up to 5 μg/L of the active ingredient), followed by the fungicide Aproach Prima® (48h-EC50: 47.33 μg of the active ingredients/L) and the herbicide Siptran 500SC® (48h-EC50: 534.69 mg of the active ingredient/L). In contrast, Siptran 500SC® was the most toxic compound (96h-IC50: 52.61 μg/L) to P. subcapitata, followed by Aproach Prima® (96h-IC50: 164.73 μg/L) and Dimilin® (non-toxic up to 1 g/L). The toxicity of the fungicide to algae and microcrustaceans demonstrates that compounds developed for certain organisms are able to affect others, indicating the relevance of conducting ecotoxicological tests on different organisms.

Abstract Studies considering the functional traits of organisms, populations, and communities functional indices increase the understanding of many factors on ecosystem functioning. Here, we analyze the predation effect (by fish) on zooplankton functional diversity and the effects of biomass and density of periphytic algae on zooplankton feeding type trait and body size. We expect that intense predation by fish on zooplankton leads to higher values of zooplankton functional diversity and that food resource will be positively related to the abundance of zooplankton trait and body size. For that, microcosms were established (T1- fish-absence, and T2- fish-presence, both with periphytic algae as food). We observed that fish presence decreased zooplankton functional diversity through modifications in the availability of nutrients and algae, through the middle-out effect. We also observed that body size had a negative relationship with the food resource, reaffirming that high food availability in subtropical lakes is linked to small-bodied zooplankton. The raptorial copepods covariate positively with the periphytic algae, which was an alternative food resource and, in this case, the main form of carbon input into the system. In this study, omnivorous fish reduced zooplankton functional traits, which can alter the energy stock and energy flow in aquatic ecosystems.

A comunidade zooplanctônica apresenta flutuação temporal estocástica e variação espacial heterogênea que são determinadas pelas relações entre os organismos e condições ambientais. Acredita-se que a distribuição temporal e espacial do zooplâncton seja heterogênea e discreta, respectivamente; e que a variação diária das espécies mais abundantes está relacionada às condições ambientais, principalmente, disponibilidade de recursos. As amostras de zooplâncton foram coletadas diariamente em três estações de amostragem em um braço lateral do reservatório de Rosana (SP/PR). O zooplâncton não apresentou diferenças significativas na abundância e equitabilidade entre as estações de amostragem, no entanto, a variação temporal desses atributos foi significativa. As variáveis abióticas e a disponibilidade de recurso algal explicou significativamente a variação diária das espécies mais abundantes (p<0,001), entretanto, a distribuição das espécies faz inferências sobre relações bióticas entre elas. Assim, não só a disponibilidade de recurso alimentar é influente na abundância das principais espécies zooplanctônicas, mas sim um conjunto de fatores (variáveis abióticas e relações bióticas).

The zooplankton community presents stochastic temporal fluctuation and heterogeneous spatial variation determined by the relationships among the organisms and environmental conditions. We predicted that the temporal and spatial zooplankton distribution is heterogeneous and discrete, respectively, and that the daily variation of most abundant species is related to environmental conditions, specifically the availability of resources. Zooplankton samples were collected daily at three sampling stations in a lateral arm of the Rosana Reservoir (SP/PR). The zooplankton did not present significant differences in abundance and evenness among sampling stations, but the temporal variation of these attributes was significant. Abiotic variables and algal resource availability have significantly explained the daily variation of the most abundant species (p<0.001), however, the species distribution makes inferences on biotic relationships between them. Thus, not only the food resource availability is influential on the abundance of principal zooplankton species, but rather a set of factors (abiotic variables and biotic relationships).

El manejo del régimen de inundación ha cambiado de manera significativa la dinámica natural de las inundaciones, que son responsables de la estructura y dinámica de las comunidades acuáticas en sistemas río-planicie de inundación. En este sentido, investigamos cómo la estructura de las comunidades zooplanctónicas responde a variaciones estacionales e interanuales en los sistemas de llanura de inundación, y los factores biológicos asociados con la abundancia de especies de las comunidades zooplanctonicas. Elaboramos también, un marco conceptual que describe los principales factores ecológicos asociados con la estructura de las comunidades para los sistemas del Alto río Paraná. Para ello se realizaron muestreos cada seis meses (potamophase en marzo y en septiembre limnophase) para caracterizar las variaciones intra e interanuales en la estructura de la comunidad entre 2000 y 2008. Las diferencias estacionales de la riqueza de especies, abundancia, índice de diversidad de Shannon y equitatividad, se llevaron a cabo utilizando procedimientos Bayesianos para mostrar predicciones probabilísticas de los datos ajustados para las principales fuentes variación. Análisis de ordenamiento no-métrico multi-dimensional (NDMS); procedimientos de permutación de respuestas múltiples (MRPP) y análisis de especies indicadoras (IndVal) fueron utilizados para evaluar y clasificar la estacionalidad de la estructura de la comunidad. Durante aguas altas (potamofase), la conectividad hidrológica favoreció el intercambio y dispersión de las especies en algunas lagunas, incrementando la diversidad local; durante aguas bajas (limnofase), la alta productividad local favoreció los táxones oportunistas, incrementando las especies dominante y disminuyendo la diversidad local. La disponibilidad de recursos alimenticios y la densidad de pequeños peces fueron los factores biológicos asociados con la dinámica estacional de la comunidad zooplanctonica; los cuales dependen de la fase hidrosedimentológica (potamofase o limnofase). Modificaciones del régimen hidrológico y limnológico relacionados con el manejo de inundación han promovido el reemplazo y empobrecimiento de la biota acuática, en las lagunas sin conexión afectadas, enfatizando así la importancia ecológica de la dinámica natural de inundaciones, que presenta pulsos regulares de inundación. El modelo conceptual que se presenta abarca desde interacciones entre diversas variables ambientales hasta mecanismos más comprensibles de las principales fuentes de variación de la comunidad.

Water flow management has significantly changed the natural dynamic of floods, which are responsible for the structure and dynamic of aquatic communities in river-floodplain systems. With the aim to elaborate a conceptual framework that describes the main ecological factors associated with zooplankton community structure in the Upper Paraná River, we investigated the mechanisms that regulate the communities structure and their response to inter-annual and hydro-sedimentological variations in the floodplain and the biological factors associated with species abundance in those communities. For this we conducted samplings every six months (potamophase in March and limnophase in September) to characterize intra and inter-annual variations in community structure between 2000 and 2008. The intra-annual differences on the species richness, abundance, Shannon diversity index, and evenness, were conducted using Bayesian procedures to show probabilistic predictions of the data fit to main variation sources. Non-metric multi-dimensional scaling (NMDS), multi-response permutation procedure (MRPP), and indicator species analysis (IndVal) were run to assess and characterize the seasonality of the community structure. During high water (potamophase), hydrologic connectivity favoured exchange and dispersal of species in some lakes, increasing local diversity; during low water (limnophase), higher local productivity favoured opportunistic taxa, increasing species dominance and decreasing local diversity. Food resources and density of small-size fish were biological factors associated with the seasonal dynamic of the zooplankton community; these factors were dependent on hydrosedimentological phase (potamophase or limnophase). Water levels and limnological modifications related to water flow management have promoted replacement and impoverishment of aquatic biota in affected lakes and have indicated the ecological importance of a natural dynamic flood, which displays regular flood pulses. The conceptual model presented encompassed interactions between diverse environmental variables to more understandable mechanisms of the main sources of community variation.

A composição e ocorrência dos rotíferos foi investigada during dois períodos hidrológicos distintos em dois ambientes (rio e lagoa). As coletas foram realizadas diariamente (14 dias) à superfície na região pelágica de cada ambiente. A similaridade faunística entre os ambientes foi avaliada através do índice de Jaccard. Foram identificados 143 táxons. O maior número de táxons foi registrado no rio. A similaridade faunística entre os ambientes foi maior no período de águas altas. Os táxons planctônicos predominaram, sendo que a diferença para os não planctônicos não foi expressiva. No rio, destacaram-se esses últimos táxons, enquanto que na lagoa prevaleceram tanto os táxons planctônicos como os não planctônicos. Verificou-se que ocorreu um maior número de táxons de menor tamanho (> 200µm a 600µm) nos dois ambientes. Esse fato está relacionado com a pequena profundidade dos ambientes e a velocidade de corrente no rio, o que permite o deslocamento dos táxons bentônicos e perifíticos do fundo e da região litorânea para a coluna de água.

Investigations were carried out for the composition and occurrence of rotifer taxa of different forms and sizes during two distinct hydrological periods, in two environments (river and lake). Two sampling stations were established in open water of each environments. Surface samples were taken daily for 14 days. The faunistic similarity between the environments was established using Jaccard's index. One hundred and fourty three taxa were identified. The largest number of taxa was recorded in the river. Faunistic similarity between these environments was greater during high water. The planktonic taxa predominated and the difference for the non-planktonic ones was not marked. Non-planktonic taxa predominated in the river, while both types were numerous in the lake. We observed a larger number of smaller-sized taxa in both environments (> 200µm to 600µm in length). This was related to the shallowest depths and to current velocity, which moved benthic and periphytic taxa from the bottom and littoral zone into the water column.