Rotifers of the upper Paraná River floodplain: additions to the checklist

Rotifers present a high diversity in freshwater ecosystems. This study registered 11 genera and 42 species, new records for the Upper Paraná River floodplain. These results showed an increase in rotifer diversity in this ecosystem from 184 to 230 species. Among them some were registered only in the rivers and others in the lagoons. Thirty-seven species occurred in the littoral zone and 34 species in the pelagic; 3 species were registered only in the former zone and 2 species only in the latter. The lagoons presented the greatest richness, probably because of the greater stability, low current velocity, and the extensive aquatic macrophyte banks in the littoral zone of these environments as compared to those of the rivers. The highest number of species in the littoral habitats occurred due to the greater influence of shoreline vegetation, which allows greater habitat diversification. This fact contributed to the occurrence of non-planktonic species in the zooplankton samples

Abundance of cladocerans in the littoral regions of two environments of the Upper Paraná River floodplain, Mato Grosso do Sul, Brazil

The abundance of cladocerans recorded in plankton samples from the littoral regions of two enviroments (Baía River and Guaraná lake), the Upper Paraná River floodplain and some limnological variables important in controlling their abundance were investigated at three sites in the lake and two in the river, from March/93 to January/94. Abundance was highest in the lake, chiefly during high water. Bosminidae dominated in both environments and hydrological periods (high and low water). Chydoridae were more important in the lake, and Sididae in the river. A higher number of Pearson's correlations significative (p < 0.03) between the densities of the ten most important species and the limnological variables was observed in the river. This suggests that limnological variables are more important in controlling the abundance of cladocerans in the river. On the other hand, in the lake their abundance was probably associated with the physical structure of the environment, the abundance of aquatic macrophytes, and biotic relationships such as competition and predation