Macrozoobenthos of the Estuary Areas of the Tributaries of the Rybinsk Reservoir

The structure and spatial distribution of macrozoobenthos in the mouth area of the small tributaries of the Rybinsk Reservoir, the Il’d, Syobla, Lam, and Yukhot rivers, was studied in different seasons, 2007–2008 and 2010–2011. The composition of the macrozoobenthos was identified: in the Il’d River, 222 species and forms, in other studied rivers, 140. Most of the discovered species were larvae of chironomids and other amphibiotic insects. The highest species richness and diversity of macrozoobenthos was recorded in the free-flow zone, and its highest abundance was recorded in the free-flow zone and in the transition zone of the tributary of the river mouth area. A significant decrease in flow in the frontal zone of river mouths leads to a decrease in species richness (due to the loss of rheophilic fauna) and creates conditions favorable for the dominance of limnophilic species adapted to oxygen deficiency, bloodworm larvae and oligochaetes.