FEATURES OF SPATIAL DISTRIBUTION OF ALIEN MOLLUSKS FROM THE GENUS <i>DREISSENA</i> IN A LARGE TRIBUTARY OF THE RESERVOIR OF THE MIDDLE VOLGA (BY THE EXAMPLE OF SVIYAGA RIVER)

Abstract

Invasions of alien species of shellfish are of great interest as a result of their serious environmental and economic consequences. We present new information on the distribution and quantitative characteristics of mollusks from the genus Dreissena in one of the tributaries of the Kuibyshev reservoir. The fact of the discovery of these species up to the upper reaches of the Sviyaga River has been revealed. The quantitative values of the Dreissena vary unevenly, gradually increasing towards the mouth of the river. Native species of mollusks dominate in the upper and middle reaches of the river, and alien ones in the lower. Comparison of morphometric characteristics of shells in the river revealed significant differences between two related Dreissenid species, with the exception of the river mouth. Important factors in the distribution and development of two species of Dreissena in the Sviyaga River are flow rate, depth and width of the river section, and the absence of a solid substrate in the water.