Environmental influence on planktonic cladocerans and copepods in the floodplain of the Upper River Parana, Brazil

The abundance of microcrustacean species recorded in plankton samples from the littoral and pelagic zones of the Upper Parana River, State of Mate Grosso do Sul, Brazil, was evaluated in relation to abiotic and biotic environmental factors. The cladocerans Bosminopsis deitersi and Bosmina hagmanni were most abundant. The presence or absence of aquatic macrophytes also influenced abundance and species composition. The true zooplankton species were most abundant at the pelagic stations, while species of Chydoridae and Macrothricidae contributed markedly to microcrustacean abundance and species richness at littoral stations. Species abundance was also strongly affected by water level variation. Microcrustaceans, mainly bosminids, were most abundant during low water. During high water, bosminids decreased in abundance while most other species increased. The higher variation of the environmental factors during high water probably explains the shift in abundance patterns. Changes in water level increased mixing of littoral and pelagic microcrustaceans between sampling stations.