Zooplankton of the Tsimlyansk Reservoir and Volga–Don Shipping Canal

— Zooplankton in the Tsimlyansk Reservoir and water bodies of the Volga–Don Shipping Canal were studied in August and September 2018. Fifteen species not previously reported in the published literature were identified in the Tsimlyansk Reservoir. A list of zooplankton (48 species) of the Volga–Don Canal is given for the first time. It is found that 60% of the abundance and 70% of the zooplankton biomass in the Tsimlyansk Reservoir are formed by Copepoda. The Ponto-Caspian Heterocope caspia and the invaders Calanipeda aquaedulcis , Thermocyclops taihokuensis, and Acanthocyclops americanus are the most abundant species. An analysis of the publications for 1952–2018 shows that most of the original Don groups of zooplankton dominants were replaced by brackish water species in the second half of the 1970s. By 2018, the mass species of Copepoda were completely replaced, among Cladocera and Rotifera, 4–6 species that were common in the Don River before its flow regulation were preserved. The biomass of the community increased more than twice (up to 2.1 ± 0.5 g/m 3 ) in 2015–2018 compared to the 40-year period before 2013. The biomass of zooplankton in the Volga–Don Canal (0.9 ± 0.4 g/m 3 ) is shown to be two times lower than in the Tsimlyansk Reservoir. The abundance of zooplankton in the water bodies of the canal is determined by Rotifera and Crustacea (50% each), and the biomass is mainly accounted for by Cladocera (49%). The species Bosmina longirostris , Chydorus sphaericus , Bosmina cf. coregoni, and Daphnia cucullata common in the Don plankton are the most abundant; the Ponto-Caspian Podonevadne trigona is developed in mass only in the Varvarovka Reservoir. The invader copepods, Thermocyclops taihokuensis , Heterocope caspia , Calanipeda aquaedulcis , and Eurytemora capsica, account for 12–23% of the crustacean population. The dynamics of the structure and abundance of zooplankton in the Tsimlyansk Reservoir in 1952–2018, as well as the dispersal and importance of Ponto-Caspian crustaceans and invaders from southern regions in plankton are discussed.