Spatial and temporal variation in densities of testate amoebae in the plankton of the Upper Parana River floodplain, Brazil

The occurrence and abundance of testate amoebae in the zooplankton of the f loodplain of the Upper Parana River was studied and compared with other zoo plankton groups. Results showed that testate amoebae were dominant zooplank ters in littoral zones of lentic and lotic environments. Species of Arcelli dae were most abundant, followed by Difflugidae and Centropyxidae. The infl uence of environmental heterogeneity (lakes or river, littoral or pelagic z ones and abiotic variables) on testate amoebae abundance was significant. A lthough significant differences were observed between different months, the patterns of abundance variation did not appear to be synchronously related to hydrological cycle. The results suggest that the high abundance of test ate amoebae in the planktonic environment of Upper Parana River floodplain is not determined only by stochastic process (washing out from the bottom a nd from the shoreline vegetation).