Veliger larvae of dreissenids (Bivalvia,Dreissenidae) in the plankton foodweb of Rybinsk Reservoir

The abundance dynamics of adult dreissenids (Dreissena polymorpha (Pallas) and D. bugensis Andrusov) and of their larvae and the spatial distribution of the abundance of veligers and their role in the functioning of the plankton community have been analyzed on the basis of the data of original long-term monitoring (2004–2013) in Rybinsk Reservoir. The dreissenid veligers are most abundant in the summer time (July to August) when their number is comparable to that of the filter-feeding crustaceans and their biomass is close to that of rotifers. Before 2010 the production of veligers during the vegetation season comprised about 5% of the production of metazooplankton and the food consumption was about 1% of the primary production of phytoplankton. Pelagic invertebrate predators consumed about 90% of the production of veligers for the vegetation period. After 2010, the abundance of dreissenid larvae and their functional characteristics decreased by a factor of 5–6. Trophic relationships between zooplankton and veligers are discussed.