The impact of the introduced crayfish Procambarus clarkii on a lake community in Tuscany.

We conducted a field experiment in a shallow oligotrophic lake in Tuscany to investigate the impact exercised by the non-indigenous crayfish, Procambarus clarkii, on mosquitofish fry (Gambusia affinis), snails (Physa sp.), and three aquatic macrophytes (Nymphoides peltata, Potamogeton sp., and Utricularia australis). The study showed that low and high densities of crayfish did not affect the survival of mosquitofish fry and U. australis but exerted a strong negative effect on gastropods and on N. peltata and Potamogeton sp. Therefore, the introduction of this crayfish species could represent a serious danger for the structure and the composition of the littoral zone communities of lentic aquatic habitats.