Long-Term Changes in the Composition and Abundance of the Zooplankton Community in Kama River Reservoirs

In August 2016, the pelagic zooplankton (Cladocera, Copepoda, and Rotifera) and meroplankton (veligers of mollusks of g.Dreissena) were studied in four reservoirs of the Kama River (Kama, Votkinsk, and Nizhnekamsk reservoirs, and the Kama Reach of the Kuibyshev Reservoir). A total of 108 species were found; 14 species were new for the Kama River, including five crustaceans introduced from the Caspian Sea. Three of them (Heterocope caspia,Eurytemora caspica, andCercopagis pengoi) spread northwards to the Kama Reservoir; two species (Cornigerius maeoticusandCalanipeda aquaedulcis) reached the upstream part of the Kuibyshev Reservoir's Kama Reach. It is revealed that five southern species (Heterocope caspia,Diaphanosoma orghidani,Pompholyx sulcata,Conochiloides coenobasisandAsplanchna henrietta) first recorded in the Kama River in 2016, locally form high abundance. The summer zooplankton biomass averages 1.8 g/m(3)in the Kama Reservoir, 1.3 g/m(3)in the Niznekamsk Reservoir, 1.0 g/m(3)in the Votkinsk Reservoir, and 0.5 g/m(3)in the Kuibyshev Reservoir; its values are similar to those recorded in the 2000s. The changes in species composition, biological invasions, patterns of spatial distribution, and long-term changes in the zooplankton biomass are discussed.