New Records of the Ponto-Caspian Predatory Cladoceran Cercopagis pengoi (Ostroumov, 1891) (Crustacea, Onychopoda) in the Water Reservoirs of the Kama and Volga Rivers

Abstract

New habitats of the Ponto-Caspian cladoceran Cercopagis pengoi in the Tetyushi, Ulyanovsk, Volga-Kama, and Kama reaches of the Kuibyshev Reservoir; the upper part of the Votkinsk Reservoir; and the lower part of the Kama Reservoir (near the city of Perm) are revealed by comprehensive studies performed at the water reservoirs of the Volga and Kama Rivers in summer 2015 and 2016. The northernmost find of the invader species was recorded in the Kama River near the town of Dobryanka (58°26′ N); thus, the species was found ≥3° further to the north in the Kama River than in the Volga River (54°57′ N). The species inhabited the uppermost 5-m water layer and the typical C. (С.) pengoi form represented the species in all the water bodies. In August, Juveniles and parthenogenetic females (body length 1.2–2.0 mm) with 2–7 embryos were observed in the water bodies, and single finds of males were made. The population size of the invader species (≤100 ind/m3) was comparable to that of the taxonomically similar hybrid form of the genus Bythotrephes (B. brevimanus × B. cederstromii) that inhabits the same areas as C. pengoi does. The routes of dispersal and the distinctive features of the spatial distribution and ecology of the species are discussed.