Comparative evaluation of dimensional characteristics of alien species of macrozoobenthos in Kuibyshev and Saratov reservoirs

New data on the dynamics of the size-age structure of massive alien species of macrozoobenthos - representatives of the Ponto-Caspian and Ponto-Azov complexes in the Kuibyshev and Saratov reservoirs of the Middle and Lower Volga are obtained. As a result of year-round research in the deep and shallow stations of the Kuibyshev and Saratov Reservoirs, it was established that the body size of Hypania invalida (Grube, 1860), Dreissena rostriformis bugensis (Andrussov, 1847), some species of amphipods (Obesogammarus obesus (Sars, 1896), Pontogammarus robustoides (Sars, 1894)) and mysids (Katamysis warpachowskyi Sars, 1893) increases in body size of individuals approximately 1.2-1.5 times, in comparison with those of the donor reservoirs (the Caspian Sea, the Dnepro-Bug estuary, rivers of the Azov Sea and the Black Sea basins). In addition, there was a significant reduction in the size of the body of large species of mysids Paramysis ullskyi Czerniavsky, 1882 and Paramysis lacustris (Czerniavsky, 1882), as well as Corophiidae Chelicirophium curvispinum Sars, 1895 and leeches Archaeobdella esmonti Grimm, 1876. Population differences in the size of individuals from donor reservoirs and recipient reservoirs are a manifestation of interpopulation adaptive relationships to environmental factors, of which the temperature factor for individual taxa is probably the determining factor. It was revealed that the dimensional structure of Dreissena polymorpha polymorpha (Pallas, 1771) in the reservoirs is characterized by the predominance of small specimens