Limnology of reservoirs in the Southeastern part of São Paulo State, Brazil. VIII. Zooplankton.

Abstract

An analysis of the zooplankton of 17 reservoirs of the State of São Paulo, from four hydrographic basins, was attempted as part of "Projeto Tipologia de Reservatórios" (FAPESP). During the year of 1979, sampling was carried out at quarterly intervals, in March, June, August, and November. The zooplankton in most of the reservoirs was numerically dominated by rotifers, which showed great species diversity. Copepods followed rotifers in eutrophic reservoirs, occurring the inverse with cladocerans. Among the group of copepods it was observed that cyclopoids were more important than calanoids, both numerically and in frequency of their occurrence. Calanoids were rather scarcely represented. At the reservoirs where the highest values of chlorophyll, nutrients and electrical conductivity were registered, together with low dissolved oxygen and water transparency values - consequently, the more eutrophic ones - calanoid copepods did not occur; the zooplanktonic community was largely dominated by rotifers (chiefly Brachionus spp). Among cyclopoid copepods, the association of Thermocyclops and Metacyclops was registered, and Bosmina sp was the most significant cladoceran. In the zooplanktonic community of less eutrophic reservoirs, the occurrence of calanoid copepods was observed, as well as a considerable decrease in importance of rotifers, which were dominated by Collotheca sp; the cladocerans presented more significant relative abundance within the community and were represented mainly by Ceriodaphnia cornuta. Concerning the cyclopoid copepods, Thermocyclops was associated with Mesocyclops. These reservoirs presented higher transparency values, and lower chlorophyll content and/or availability of nutrients compared to the group of reservoirs described above.