Distribution of Some Ponto-Caspian and Alien Copepods (Crustacea, Copepoda) in Plankton of the Don River Basin

In 2018-2019, the zooplankton was studied in the Don River from the source to the mouth including the Tsimlyansk Reservoir, Volga-Don shipping canal, and the upper part of Taganrog Bay of the Sea of Azov. Habitats of two Ponto-Caspian species of copepods ( Heterocope caspia and Eurytemora caspica ) and of three alien species, Mediterranean copepod Calanipeda aquaedulcis , a representative of the neritic zone Acartia ( Acanthacartia ) tonsa and East Asian euryhaline Thermocyclops taihokuensis were found. For the first time, the findings of T. taihokuensis were recorded in the Don River upstream and downstream of the Tsimlyansk Reservoir and in water bodies of the Volga-Don shipping canal. It is shown that the Ponto-Caspian Eurytemora caspica inhabits the Don River basin and Taganrog Bay of the Sea of Azov. The European copepod E. affinis which was previously recorded in the region was not found in the studied areas of the basin. The occurrence (>80% of samples) of the Ponto-Caspian species and Calanipeda aquaedulcis was the highest. A recent invader Thermocyclops taihokuensis reached the maximum abundance (>100 000 ind./m). By an example of the Tsimlyansk Reservoir, it is found that the way of the spread of the Ponto-Caspian and alien species in the Don River basin may be large-scale activities on the introduction of planktonic and benthic invertebrates conducted in the 1950-1970s in order to improve the food supply of valuable fish species. The history of dispersal of the studied copepod species and their population characteristics are discussed.