Invasive molluscs in Umbrian inland waters: ecological and reproductive aspects

Invasive molluscs in Umbrian inland waters: ecological and reproductive aspects The increasing colonisation by aquatic invasive molluscs has only recently received scientific attention in Umbria, notwithstanding the possible great impact on the functionality and biodiversity of the freshwater ecosystems. The present contribution highlights the results of investigations carried out on Dreissena polymorpha (Bivalvia) in Lake Trasimeno and on Potamopyrgus antipodarum (Gastropoda) in water courses of the Tiber River basin. This in view to evaluate the impact of habitat type on colonisation and reproduction. Dreissena polymorpha showed a marked selectivity for natural and artificial hard substrates. This preference gives inception to competition with the sponge Ephydatia fluviatilis (Porifera), which overgrow the mollusc, thereby encapsulating its valves. The study of the life cycle showed a tight link between gonadal development and water temperature, the high values of which limit larval development and species dispersal. Analyses on parthenogenetic populations belonging to P. antipodarum showed a different fecundity in relation with habitat type, and the marked selectivity towards various biological substrates (macrophytes, decaying organic materials, periphyton, etc.). The scarce availability of these components together with high current speed, limit the colonisation ability of this species.