Distribution and special traits of naturalization of new and rare zooplankton species in waterbodies of the Upper Volga basin

More than ten new zooplankton species were registered in reservoirs of the Upper Volga during 2002-2005. Since 2003, the cladoceran Diaphanosoma orghidani Negrea, had intensively settled in different biotopes of Ivankovo, Uglich, Rybinsk, and Sheksna reservoirs and is the most abundant (16 000 ind./m(3)) in the latter one. The rotifer Asplanchna henrietta Langh. was found for the first time in Rybinsk Reservoir in 1985, and by 2004, this species had also occurred in Ivankovo, Uglich reservoirs, Lake Nero, and some small waterbodies of the basin. In Lake Nero its density reaches especially high values (> 1 million ind./m(3)). Causes, mechanisms, and ecological consequences of the expansion of new zooplankton species are discussed.