Invasive crayfishhes as a threat to native freshwater bivalves

Procambarus clarkii and Pacifastacus leniusculus are problematic invasive species and may affect freshwater bivalves. In this study we verified ifthese crayfish species can predate native (Anodonta anatína, Potomida littoralis and Unio delphinus) and non-native (Corbicula fluminea) bivalves through experiments in laboratory and validation in the field (Sabor basin, North of Portugal). In the laboratoiy, crayfish feeding preferences and competition between the two crayfish species were also assessed. In the field, abundances and lengths of the specimens of each bivalve species were recorded, crayfish predation marks on bivalves were quantified and crayfish distribution, abundance and sexwere determined. AU native bivalve species were preyed both in laboratoiy and in the field; however, P. clarkii and P. leniusculus were unable to prey the non-native C. fluminea. Bivalve predation was not afifected neither by the length or sex ofthe crayfish. The most preyed native species by both crayfishes was A. anatina. We also found competition for bivalves as a prey between the crayfishes, being P. clarkii dominant and displaying a more aggressive behaviour than P. leniusculus. Results of this study support the idea that P. clarkü and P. leniusculus can affect native bivalves by decreasing the number of effectives by increasing mortality and by reducing their fítness, which may have indirect impacts on freshwater ecosystems. On the other hand, and since crayfishes did not prey C. fluminea offers this invasive bivalve another advantage over native species. FinaUy, we also assessed the predation ofP. leniusculus on Margaritifera margaritifera in the Tua basin (North of Portugal) and our results confirm this invasivc crayfish as a threat to pearl mussels. Therefore, future management actions devoted to the conservation of freshwater bivalves should have in account the possible effects of invasive crayfishes on these organisms.