We investigated the effect of interannual variation of hydrosedimentological regime and connectivity on the zooplankton biodiversity in the Upper Paraná River floodplain. Zooplankton samplings were undertaken between 2000 and 2007, in different environments of the floodplain, including connected and isolated floodplain lakes, backwaters, rivers and channels. The zooplankton included 541 species. Rotifers showed the highest species richness and abundance. Among the zooplankton species, 71 represent new occurrence records for the floodplain. The species accumulation curve showed a continuous increase in gamma diversity, demonstrating the importance of long-term research for accurate knowledge of biodiversity in heterogeneous and dynamic ecosystems, such as the floodplains. Interannual beta diversity among studied years indicated a lesser alteration in community composition in 2001, when a long limnophase period was observed. In most of the environments, the highest species richness values were related to the greatest flooding amplitudes. Flooding amplitude, which is associated with connectivity, favors faunal exchange amongst the environments and between the pelagic and littoral zones. This explains the occurrence of both planktonic and non-planktonic species within the community. On the other hand, mean zooplankton abundance values were higher when a long isolation period occurred. Differences between the potamophase and limnophase amplitude associated with connectivity among the environments were the most important factors for the structure and dynamics of the zooplankton community in the Upper Paraná River floodplain.

This study investigated the effects of fish farming on phytoplankton and zooplankton structure in a Brazilian tropical reservoir. Samplings were undertaken among 15 net cages and upstream and downstream of the cages over a 120-day period. Soon after the tilapia feeding, we observed the highest density of phytoplankton, with dominance of Cyanobacteria which probably increased due to the increase in predation pressure by cladocerans and copepods on the Cryptophyceae. However, after 30 days from that, a reduction in zooplankton density was registered due to the dominance of Cyanobacteria. The absence of a clear spatial difference in the phytoplankton and zooplankton densities was observed. The effects of the net cages on the nutrients and planktonic communities were small, probably due to the low number of net cages and fish employed, the seasons (autumn/ winter) and the hydrodynamics, as lotic traits, the strong influence of the wind, and the large extension of the mixture zone.

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Aim Evaluating how groups of organisms vary in dispersal capability and how environmental, spatial and temporal signals vary across multiple scales is critical to elucidating metacommunity theory. We examined whether the relative contributions of environmental, spatial and hydrological factors have different effects on organismal groups with different dispersal abilities at three spatial scales, and how this knowledge contributes to our understanding of metacommunity dynamics. Location Four major Brazilian floodplains, with the largest distance among them of 2,300 Km. Taxon 10 aquatic organismal groups, ranging from bacterioplankton to fish. Methods We sampled lakes connected to the main river in the low‐ and high‐water periods of each floodplain between 2011 and 2012. Different biological groups were analysed across three hierarchical spatial scales (fine, intermediate and subcontinental) within and between floodplain systems. We applied a series of partial redundancy analyses to estimate the relative contributions of environmental factors, spatial factors and hydrological period for each biological group. Results At the fine spatial scale, predominantly environmental factors and hydrological period structure metacommunities, although less so for microorganisms than for micro‐invertebrates and macro‐organisms. The relative importance of environmental factors increased at the intermediate spatial scale. At the subcontinental scale, the relative importance of spatial factors increased for all biological groups, but environmental factors remained the primary regulators of microorganisms even at the largest scale. Main conclusions This study design allowed us to make more robust inferences about the mechanisms responsible for regulating community structure of distinct biological groups at different spatial scales. Our results suggest that biological groups displaying distinct body size likely determine the spatial extent at which environmental, spatial and hydrological processes prevail as the primary regulators of community structure. These findings are important in guiding the conservation and management of floodplain biodiversity because these systems are naturally highly heterogeneous in space and time.

Iheringia, Série Zoologia, Porto Alegre, 101(1-2):75-84, 30 de junho de 2011 Impact of fish cage-culture on the community structure of zooplankton... ABSTRACT. We investigated the impact of fish cage culture on the zooplankton community structure in a tropical reservoir. We hypothesized that community abundance is greater near cages and increases over time due to the increase in food availability. Samplings were performed near, upstream and downstream from net cages, and before and after net cage installation. The abundance of zooplankton increased 15 days after the experiment was set up, followed by a reduction and finally increased. Rotifer abundance showed significant differences among sites (p<0.05) and sampling periods (p<0.001). Significant differences were also observed in total zooplankton and cladoceran abundance (p<0.001). The spatial and temporal variation of the physical and chemical variables were indirectly correlated with the structure and dynamic of the zooplankton community, as they indicated the primary production in the environment. Our hypothesis was rejected, since the zooplankton was abundant at the reference site. Only rotifers showed higher abundance near cages, due to the influence of food availability. Community dynamics during the experiment was also correlated to food availability. Our results suggest an impact of fish farming on the zooplankton community. Impact of fish cage-culture on the community structure of zooplankton in a tropical reservoirKEYWORDS. Aquaculture, tilapia, environmental impact.RESUMO. Impacto da piscicultura em tanques-rede na comunidade zooplanctônica em um reservatório tropical. O objetivo deste estudo foi investigar o impacto da piscicultura em tanques-rede sobre a estrutura da comunidade zooplanctônica em um reservatório tropical. Acredita-se que a abundância do zooplâncton é maior perto dos tanques-rede e aumenta ao longo do tempo devido ao aumento da disponibilidade de alimento. As coletas foram realizadas próximo aos tanques-rede, bem como a montante e a jusante dos mesmos, antes e após a instalação dos tanques. A abundância do zooplâncton aumentou 15 dias depois da instalação dos tanques, seguida por uma redução e posterior aumento no fim do experimento. A abundância dos rotíferos apresentou diferenças significativas entre os pontos (p<0,05) e períodos de amostragem (p<0,001). Diferenças significativas também foram observadas para a abundância do zooplâncton total e de cladóceros (p<0,001). A variação espacial e temporal das variáveis físicas e químicas apresentou uma relação indireta com a estrutura e dinâmica da comunidade zooplanctônica, pois essa variação indicou a produção primária no ambiente. A hipótese foi rejeitada, pois o zooplâncton foi mais abundante no ponto de controle. Apenas os rotíferos apresentaram maior abundância perto dos tanques, devido à influência da disponibilidade de alimento. No entanto, a dinâmica da comunidade durante o experimento também foi relacionada com a disponibilidade de alimento. Os resultados sugerem o impacto da pi...