Benthic malacofauna of the reservoirs of the middle River Tietê (São Paulo, Brazil) and an ecological evaluation of the invasive exotic species, Melanoides tuberculata (Müller) and Corbicula fluminea (Müller).
The species composition, density and spatial and temporal distribution of the benthic malacofauna in 3 reservoirs of the middle Tietê River in São Paulo, Brazil, were investigated. Sampling was carried out during the rainy season in November 2002 and the dry season in August 2003. Three portions in each reservoir (upper, middle and lower) were sampled using the sweeping method, and 6 sampling points were used in each transect. The reservoirs eutrophied with high concentrations of nutrients (total and dissolved). Eight species of molluscs were registered (6 native and 2 exotic). Of these, the dominant species was the exotic and invasive Melanoides tuberculata, which was found in all the reservoirs. Another exotic species, Corbicula fluminea, was observed in all reservoirs in both periods of sampling (except in the Barra Bonita reservoir). In the Barra Bonita reservoir, only the 2 exotic species occurred, while in the Bariri and Ibitinga reservoirs, the native species Aylacostoma tenuilabris, Biomphalaria glabrata, Biomphalaria intermedia, Diplodon expansus, Physa cubensis and Pomacea canaliculata occurred during at least one of the sample periods. The widespread distribution of M. tuberculata and C. fluminea, and the high densities of these species in the studied reservoirs revealed the invasive potential of these species and their probable competition with native species.