Sea), which is subject to the strong influence of the river discharge, are presented. The number of species at the
sampling stations varied from 4 to 65. The density of the communities and the zoobenthos biomass ranged from
342
68 to 4293 96 ind./m2 and from 0.418 0.081 to 1975.22 494.36 g/m2, respectively. The Shannon index values varied between 1.19 to 4.7 bit/ind. At the upper part of the estuary, detritivores dominated, while,
in the central part and at outlets, sestonophages prevailed. The changes in the quantitative indices of the zoob-
enthos along the gradient of the water salinity were traced, and the relations of these indices with seven more
environmental factors were revealed. It was found that the species composition, the biodiversity, and the trophic
structure of the zoobenthos significantly correlate with some of the above mentioned parameters. Multiple
regression analysis was used to assess the combined effect of the factors, and it revealed which of them play a
determining role in Kemskaya Bay: for the species composition, these are the depth, the water color, and the
content of total suspended matter; for the number, these are the contents of pelite and Corg in the bottom sedi-
ments. The biomass depends on the water salinity, the water chromaticity, and the Corg contents in the sediments
and suspended matter. The Shannon index value is determined by the water color, the Corg contents in the sed-
iments, and the pelite content. The calculations of the ecological stress values revealed two zones with an unsta-
ble state of the zoobenthos.