On distribution of Dreissena bugensis (Dreissenidae, Bivalvia) in reservoirs of the Upper Volga River basin [Russian]

摘要

The current distribution of Dreissena bugensis was studied in Ivan'kovo, Uglich, and Rybinsk reservoirs (the Upper Volga River basin) within its predetermined range according to the accepted network of experimental stations of the Institute for Biology of Inland Waters. The D. bugensis settlements were recorded on the slopes of the former riverbeds in the Uglich and Rybinsk reservoirs (frequency of their occurrence is about 100%). In the Uglich reservoir, this species was found for the first time. In the Ivankovo reservoir as well as in Mologa and Sheksna areas of the Rybinsk reservoir, D. bugensis was not recorded. In the Uglich and Rybinsk reservoirs, the size structure of D. bugensis and D. polymorpha polulations differed significantly. Despite the high abundance and extended area of the new invader, its populations were mainly composed of individuals of 2+ - 3 + and older. The Upper Volga polulations is not considered as a completely developed. The invasion of D. bugensis to the Volga basin is suggested to be effective in the late 1980s and early 1990s via the Volga-Don Canal. Later on, its area is extended naturally to the Volga delta and the areas with freshened water in the Caspian Sea as well as to the Upper Volga due to influence of anthropogenic factors. The transformation of the Volga River to a region-donor of the secondary D. bugensis introduction and a probable intense use of the Volga-Baltic Sea waterway may promote the further anthropogenic spreading of it to reservoirs of the North-Western region.