Ecosystem of Caspian Sea threatened by pet-traded non-indigenous crayfish

Freshwater ecosystems are particularly vulnerable to biological invasions; the aquatic animal pet trade has been recognized as a significant pathway of introductions. Crayfish are considered a model group of traded organisms with a series of highly successful species already established in the wild, having the potential to negatively influence both indigenous crayfish species (ICS) as well as alter occupied ecosystems. Eastern Europe includes the entire native ranges of indigenous Astacus leptodactylus sensu lato and A. pachypus. This region has been largely overlooked and considered relatively safe from the adverse impacts of non-indigenous crayfish species (NICS). In this study, we evaluated the crayfish pet trade in the Lower Volga Region with special emphasis on Astrakhan, the biggest city of Russian Federation in the region located just in the delta of Volga River, thus being a potential gateway of introductions to the Caspian Sea and adjacent freshwaters. The local pet trade involves 12 NICS. Considering their origin, availability, probability of establishment, invasiveness and further aspects, Procambarus fallax f. virginalis, P. clarkii and Cherax destructor are considered potentially the most problematic, including transmission of diseases like crayfish plague caused by Aphanomyces astaci or white spot syndrome virus. Taking this information as a whole, the availability of NICS with a high probability of overlapping the entire range of European ICS means that attention is warranted. Further research is needed to corroborate the abilities of NICS and their associated diseases to withstand specific conditions of the Caspian Sea as well as the adjacent Black and Azov Seas, all possessing different degrees of elevated salinity.