[Factors of macrozoobenthic communities formation on stony rapids and bars in streams of East Fennoscandia].

Relying on own data (267 quantitative samples in total), factors of rheophilous zoobenthos formation in East Fennoscandia have been studied with use of detrended correspondence analysis. In the period from 2005 to 2011, in August, samples were taken from 90 stony rapids belonging to 39 streams. On East Fennoscandia territory, which extends over 1000 kilometers in south-north direction, climatic factor plays an important role in formation of macrozoobenthos in streams. With regard to both species composition and total abundance, the poorest benthic communities are found in tundra rivers in the northern part of the region. In limnetic-riverine systems of south Karelia, on the contrary, rheophilous macrozoobenthos is characterized by great number of species and high biomass. However, the structure of benthic communities is markedly influenced, beside the climate, by flowing lakes and settlements located in the catchment area. Under their influence, the species richness of zoobenthos in streams decreases while the biomass increases. Under the conditions of low trophic status that are indicative of northern water bodies, these sources of additional organic matter and biogenic elements improve feeding conditions for macrozoobenthic organisms which, in its turn, leads to biomass and production growth.