The Spread of East Asian Copepod Thermocyclops taihokuensis (Crustacea, Copepoda) in the Volga River Basin

In 2016–2019, the copepod Thermocyclops taihokuensis (Harada, 1931) was found in four areas of the Volga River basin, which are 270–1000 km apart from each other. The invader lives in the Lower Volga (river section from the village of Cherny Yar to the city of Astrakhan), in the two areas of the Middle Volga (lake-like part of the Cheboksary Reservoir, the Volga and Volga-Kama reaches of the Kuibyshev Reservoir), and the upper reaches of the Oka River basin (Shat Reservoir). The invader density varies from less than 1 to more than 100 000 ind./m3. To the north of European Russia, the species settled up to 56° N (mouth of the Sura River), to the west, up to 38° E (Shat Reservoir). In the Lower Volga, the invader was the most abundant representative of Cyclopoida and lived together with native Th. crassus. In the Cheboksary and Kuibyshev reservoirs, it coexisted with native Th. oithonoides and Th. crassus; native species dominated. The competitiveness and successful naturalization of Th. taihokuensis in European Russia is determined by its high fertility and long breeding period.