Invasions of New Morphotypes of Corbicula fluminalis and Corbicula fluminea (Bivalvia: Corbiculidae) to the Basin of the Dagestan Region of the Caspian Sea

The article reports the discovery of populations of Corbicula mollusks in the south of the European part of Russia (43° N, 47° E). Representatives of the genus Corbicula are included in the 100 most actively spreading alien species. The aim of the study was to identify species and morphotypes in the Caspian Sea basin. For the first time on the territory of the Russian coast of the Caspian Sea at the mouth of the Sulak River in November 2019, two live specimens of the new morphotype B/Rlc of Corbicula fluminea (eastern Corbicula , Asian clam) (O.F. Müller, 1774) were found. In November 2021, 26 live individuals of the A/R C. fluminea morphotype were found in the Yuzbash-Sulak Reservoir; 13 individuals of the A/R morphotype and 90 specimens of the C/S morphotype of Corbicula fluminalis (O.F. Müller, 1774) in the Prisulak Canal were found. A study of the morphometric parameters of the shells showed that the Asian clams found belonged to different morphotypes, with well-distinguishable conchiological signs. The data obtained expand the understanding of the morphological variability of Asian clams. A study of the species and size–age composition of populations was carried out. It was revealed that C. fluminea and C. fluminalis discovered on the Dagestan coast were new species and morphtypes of Asian clams for the Russian sector of the Caspian Sea. The studied samples were dominated by mollusks of size and age groups corresponding to the age from 1.5 to 3 years, which indicated a recent settlement into a new water body for them. The populations of C. fluminalis studied from 2017 to 2021 were dominated by mollusks aged 5–6 years, which indicated an earlier invasion of this species. High physiological tolerance combined with different breeding strategies of the representatives of the genus Corbicula gives grounds to assume a high probability of their successful naturalization in estuarine and freshwater ecosystems of the Dagestan region of the Caspian Sea.