Spreading of Alien Zooplankton Species of Ponto-Caspian Origin in the Reservoirs of the Volga and Kama Rivers

Zooplankton was studied in August 2015–2017 in eight reservoirs of the Volga River, in an unregulated part of the river between the cities of Volgograd and Astrakhan, and in three reservoirs of the Kama River. The Ponto-Caspian species were recorded in the Volga River downstream of the city of Kazan (south of 55°32′ N) and in the Kama River from the mouth to the upper reaches of the Kama Reservoir (59°20′ N). Six alien species ( Heterocope caspia , Calanipeda aquaedulcis , Eurytemora caspica , Cornigerius maeoticus maeoticus , Cercopagis pengoi , and Podonevadne trigona ovum ) were recorded in the Volga reservoirs and three species ( Heterocope caspia , Eurytemora caspica , and Cercopagis pengoi ) were recorded in the Kama reservoirs. It was found first time that copepods Heterocope caspia and Eurytemora caspica spread and naturalized in the areas of all three Kama reservoirs (within the distance of 1000 km from the Volga River); the cladoceran Cercopagis pengoi formed a disrupted range with a group of habitats in the mouth part of the Kama River (55°12′–55°26′ N) and north near the city of Perm (57°53′–58°26′ N). The boundary of the ranges of Calanipeda aquaedulcis , Cornigerius maeoticus , and Cercopagis pengoi shifted 300–400 km to the north in the Volga River and 300 km in the Kama River; they occupied almost all area of the Kuibyshev Reservoir except for the upper reaches of its Volga part. The range expansion of the cladoceran Podonevadne trigona ovum was not observed; this species was found only in the Volgograd Reservoir (46°18′ N). It was revealed that by 2017 the Mediterranean copepod Calanipeda aquaedulcis had become common (occurrence in more than 90% of samples), locally numerous in the Volga River from the city of Astrakhan (52° N) to the mouth of the Kama River (55°12′ N) and in the Kama River from the mouth to the upper reaches of the Kama part of the Kuibyshev Reservoir (55°24′ N). It is revealed that a new species Eurytemora caspica (described in 2013), but not E. affinis (as it was believed earlier), lives in the Volga and Kama rivers. The prospects of the further spread of Ponto-Caspian species up the Volga and Kama rivers and their role in the zooplankton in water bodies are discussed.