1. Despite the growing number of non-indigenous crayfish species introduced worldwide, little scientific attention has been given to their effects on the recipient communities. Here, we quantified the impact of adult red swamp crayfish (Procambarus clarkii) on key components of the littoral community of a mesotrophic lake in central Italy. We used two densities of crayfish plus a no-crayfish control, and two complementary methods –in situ enclosures and a laboratory study.
2. Both experiments showed that P. clarkii strongly affects the community even at a low density (4 m−2), although a high crayfish density (8 m−2) showed a more pronounced impact in a shorter time.
3. In enclosures, P. clarkii quickly consumed the pond snail Haitia acuta, notwithstanding its anti-predator behaviour, but not the mosquitofish Gambusia affinis. The biomass of the hydrophytes Nymphoides peltata and Potamogeton spp. was strongly reduced by crayfish grazing, coupled with their non-consumptive plant clipping and uprooting, which were particularly intense in the case of Potamogeton crispus. In contrast, Utricularia australis was avoided by P. clarkii, even when other resources were exhausted.
4. The introduction of P. clarkii could reduce biodiversity and increase biotic homogenisation in a short time.