Species composition of benthic molluscs in the reservoirs of the lower Tietê River (São Paulo, Brazil), with an evaluation of the impact of exotic invasive species.
The taxonomic composition, density and spatial distribution of benthic molluscs in reservoirs of the lower Tietê River, São Paulo, Brazil, were studied in November 2002 and August 2003. The exotic species Melanoides tuberculata was distributed in all the localities sampled and was the most abundant species, corresponding to ≥65.9% of the total abundance, and was dominant in all the reservoirs, with a maximum density of 23 753 individuals m-2 recorded at a depth of 2 m at the upper part of Nova Avanhandava reservoir. The other exotic species, Corbicula fluminea and Helisoma sp., were much less abundant and they were not registered in all parts of the reservoirs. The native species were Aylacostoma tenuilabris, Biomphalaria glabrata, B. intermedia, Physa cubensis and Pomacea canaliculata. These species contributed less than 20% of the total abundance of molluscs in the reservoirs, occurring at low densities, much lower than those of the exotic species (mainly M. tuberculata), possibly indicating the impact of exotic invasive species on native populations.