Relative Distributions of Dreissena bugensis and Dreissena polymorpha in the Lower Don River System, Russia key words: zebra mussels, quagga mussels, dreissenid abundances, invaders, mineral content
AbstractA survey was conducted in the lower Don River system in Russia to confirm the presence of Dreissena bugensis, and to compare its distribution relative to that of Dreissena polymorpha. In 1999 and 2001-2002, dreissenid mussels were collected at 15 sites in the main river, in connecting reservoirs, and in a major tributary, the Manych River. Collections were made near stations where long-term monitoring data on total mineral (sum of principal ions) and calcium content were available. Both dreissenid species were found at all sites, with D. bugensis comprising 4-75% of all dreissenids at individual sites. D. bugensis was relatively more abundant than D. polymorpha in the Manych River where total mineral and calcium content was significantly higher than in the Don River, suggesting the two species may have different calcium requirements. Examination of archived samples indicated that D. bugensis was present in the Don River system as early as the 1980s, presenting the unresolved enigma of why D. bugensis has not displaced D. polymorpha as the dominant species as typically found over shorter time periods in other water bodies.
IntroductionThe expansion of species outside of their native ranges has become a world-wide problem (CARLTON and GELLER, 1993;LODGE et al., 1998). Once introduced into a new environment, these invasive species often rapidly increase in number and may cause complex changes in food web structure and ecosystem processes. Given the importance of the problem, information on the biology and distribution patterns of these species within their native ranges may provide a better understanding of how populations respond in newly invaded systems. Two dreissenid species, Dreissena bugensis (ANDRUSOV, 1897) (quagga mussel) and Dreissena polymorpha (PALLAS, 1771) (zebra mussel), provide examples of invaders that now occupy vast areas far removed from their original places of origin. Dreissena bugensis originated from a quite restricted region in the Bug River where it was first described (ANDRUSOV, 1890). It was later found in the nearby Bug-Liman Delta, and in reservoirs in the Ukraine (ZHURAVEL, 1951;KHARCHENKO, 1995). Within Eastern Europe, the first finding of the quagga mussel far removed from its natural range occurred in 1992 in the mid-Volga Internat. Rev. Hydrobiol.