Calanoida (Copepoda) species composition changes in the reservoirs of São Paulo State (Brazil) in the last twenty years

Among the zooplankton groups the Calanoida copepods present a high degree of endemism with a very restricted geographic distribution. This endemism can be a response to the sensibility of these organisms to changes in chemical and physical factors such as pH, conductivity and ionic ratios. Studies on the composition and distribution of the Calanoida species in 21 reservoirs of São Paulo State, carried out from 1979 onwards, and the studies on Barra Bonita Reservoir show a complete change in species composition including the appearance of a new species. Species which were frequent such as Notodiaptomus conifer in the majority of the reservoirs of the Middle Tiet^e and Paranapanema River basins, disappeared completely, being substituted by other species. At the Barra Bonita Reservoir, species such as Argyrodiaptomus furcatus,and Scolodiaptomus corderoi, which are typical of waters of low conductivity (up to 100 μS cm−1 ) and pH near 7.0, were substituted by species of Notodiaptomus iheringiand N. cearensis dwellers in waters of conductivity much higher than 100 μS cm−1 (up to 500 μS cm−1) and lower pH than 7.0. Structural changes in the zooplankton community can be the first step towards large scale changes in reservoir functions as a consequence of eutrophication and toxicity.