Distribution of Eurytemora caspica Sukhikh & Alekseev, 2013 (Copepoda, Calanoida) in the water reservoirs of the Volga and Don river basins

Abstract The zooplankton composition of the Volga, Kama and Don rivers was studied in the summers of 2015-2018. The copepod Eurytemora caspica Sukhikh & Alekseev, 2013, recently isolated from the group of species contained in Eurytemora affinis, represents a widespread (50-100% of samples) and relatively abundant (maximum abundance up to 18 × 103 ind./m3) species. It is found in the Lower and Middle Volga from the city of Astrakhan to the mouth of the Kama River, in the Kama River to the upper reaches of the Kama reservoir, in the lower and middle sections of the Don River within the Tsimlyansk reservoir, as well as in the reservoirs of the Volga-Don shipping canal. In the Kama River, E. caspica was discovered by the author for the first time in 2016. In other habitats, it was previously identified as Eurytemora affinis (Poppe, 1880), although this particular species was not found in any of the analysed samples. The distribution features and habitat conditions of Eurytemora caspica in the rivers of the basins of the Caspian and Azov seas are discussed.