The impact of impoundment on the rotifer communities in two tropical floodplain environments: interannual pulse variations.

Hydrological pulses are the main factor regulating the structure of biological communities in floodplains. Reservoirs above this ecosystem change the environment's dynamics and the community's biodiversity. This study evaluated the structure and stability of the rotifer community in response to changes in hydrological pulses after the Porto Primavera impoundment in the Upper Paraná River floodplain. The community was studied in a river and in a floodplain lake downstream of the dam over a four-year period before and after the impoundment. A decrease in species richness and abundance was observed soon after the impoundment, followed by an increase in these attributes and in specific diversity when the hydrometric level of the Paraná River rose and, consequently, increased the connectivity between the floodplain environments. Conochilus coenobasis, Filinia longiseta, Keratella cochlearis, Lecane proiecta and Polyarthra dolichoptera persisted throughout the study and contributed to community stability (the maintenance of rank in species abundance over time), which was high in the floodplain lake, mainly after the impoundment. Reductions in the frequency, intensity and amplitude of potamophase pulses after the impoundment led to the decrease in species richness and the increases in abundance, community stability, and species diversity, which determine community resilience.

The impact of impoundment on the rotifer communities in two tropical floodplain environments: interannual pulse variations / O impacto de represamentos sobre comunidades de rotíferos em dois ambientes de planície tropical: variações interanuais nos pulsos hidrológicos

Hydrological pulses are the main factor regulating the structure of biological communities in floodplains. Reservoirs above this ecosystem change the environment's dynamics and the community's biodiversity. This study evaluated the structure and stability of the rotifer community in response to changes in hydrological pulses after the Porto Primavera impoundment in the Upper Paraná River floodplain. The community was studied in a river and in a floodplain lake downstream of the dam over a four-year period before and after the impoundment. A decrease in species richness and abundance was observed soon after the impoundment, followed by an increase in these attributes and in specific diversity when the hydrometric level of the Paraná River rose and, consequently, increased the connectivity between the floodplain environments. Conochilus coenobasis, Filinia longiseta, Keratella cochlearis, Lecane proiecta and Polyarthra dolichoptera persisted throughout the study and contributed to community stability (the maintenance of rank in species abundance over time), which was high in the floodplain lake, mainly after the impoundment. Reductions in the frequency, intensity and amplitude of potamophase pulses after the impoundment led to the decrease in species richness and the increases in abundance, community stability, and species diversity, which determine community resilience.

O principal fator regulador da estrutura das comunidades biológicas nas planícies de inundação é o regime de pulsos hidrológicos. Reservatórios construídos nesses ecossistemas alteram a dinâmica dos ambientes e a biodiversidade das comunidades. Este estudo avaliou a estrutura e a estabilidade da comunidade de rotíferos em conseqüência das alterações do pulso hidrológico após o represamento de Porto Primavera, na planície de inundação do Alto Rio Paraná, a montante. A comunidade foi estudada em um rio e uma lagoa, durante quatro anos, antes e depois da construção do reservatório. Logo após o represamento, foi observada a redução da riqueza de espécies e abundância dos organismos, seguida do incremento destes atributos, e da diversidade de espécies com o aumento do nível hidrométrico do Rio Paraná e, conseqüentemente, da conectividade entre os ambientes da planície de inundação em anos de cheias excepcionais. Conochilus coenobasis, Filinia longiseta, Keratella cochlearis, Lecane proiecta e Polyarthra dolichoptera persistiram durante o estudo, contribuindo para a estabilidade da comunidade (manutenção da abundância das espécies ao longo do tempo), que foi maior na lagoa, principalmente após o represamento. A redução na freqüência, intensidade e amplitude dos pulsos de potamofase determinaram, por um lado, a redução da riqueza de espécies, e por outro o aumento da abundância dos organismos e da estabilidade da comunidade, além do aumento da diversidade de espécies, favorecendo a persistência da comunidade.