Polychaete Hypania invalida (Polychaeta: Ampharetidae) in the Kuybyshev Reservoir: Distribution and size and weight parameters

Hypania invalida (Grube, 1860), one of three common polychaete species for the Kuybyshev Reservoir, was found for the first time in the mid-1970s. It recently became a common benthic species, despite its low density and biomass. This polychaete can be found quite often at depths of more than 5 m, in silty deposits, and in communities formed by two dreissenid species (Dreissena polymorpha and D. bugensis) , which are the most abundant in zoobenthic communities. The polychaete abundance depends weakly on the abundance of dreissenids in communities. However, the polychaete average body size, abundance, and biomass are the highest in the communities where the dreisssenid contribution to the total biomass constitutes 10.1 to 50.0%. For the last 10–15 years, the average polychaete body weight has tended to decrease; the same is observed for its abundance in the dreissenid communities. The seasonal dynamics of polychaete populations and its reproduction peculiarities are estimated on the basis of data on its abundance and body weight.