Interactions between invasive crayfish and native river shrimp

In the south of Portugal there are only two species of strictly freshwater decapods: the native freshwater shrimp Atyaephyra desmarestii and the exotic crayfish Procambarus clarkii. The aim of this study is to understand if the exotic crayfish acts as river shrimp predator and if both species share the same type of microhabitat. We performed laboratory experiments to study predation and conducted field work in the river Sorraia to verify the microhabitat distribution of both species. Laboratory experiments demonstrated significant predation on river shrimp for crayfish with a cephalothorax length (CT) over 24 mm. The average daily consumption increases with crayfish CT to a maximum of 0.8 shrimps at 44 mm. Field work confirmed that both species share the same microhabitats although with small differences e. g. on the water quality variables such as conductivity and the percentage of oxygen saturation. These microhabitats are shallow pools with abundant aquatic vegetation with no preference for the type of substrate. In the field, both crayfish density and its cephalothorax length are negatively correlated with shrimp densities. In conclusion, P. clarkii can predate A. desmarestii and the major impacts are expected at high densities of large sized crayfish.