Abstract. Aim. Beysugsky Estuary is one of the biggest estuaries of the Azov-Kuban’ lowland. Like the other water bodies in the South of Russia, this one is subject to strong anthropogenic load: detachment of the freshwater part for establishing the Beysug spawning area; regulation of the flow of the rivers feeding the estuary; destruction of the Yasenskaya spit and narrowing of the Bugaz mouth; disorganized tourism. The ongoing reformation of the ecosystem makes it necessary to carry out the analyses of the modern state of the biota of this water body and uncover reasons and regularities of its change.

Location. Beysug Estuary of the Sea of Azov.

Methods. Quantitative zoobenthos samples were taken with the Petersen dredger (sampling area 0,034 m2) from board of the inflatable “Zodiac” boat. Qualitative samples were taken in the coastal zone by hand and with the dredge. All the samples taken were washed through the bag made of mill sieve with mesh size 0,5 mm, and then were fixed in a plastic bucket by 4 % formaldehyde (quantitative samples) or 70 % ethyl alcohol (qualitative samples). Taking and processing of samples were carried out in field and laboratory environment using common methods. 22 samples at 7 stations were taken in total.

Results. Macrozoobenthos was presented by 14 invertebrate species. Estuarine fauna is the depleted version of the euryhaline one of the Sea of Azov with Holocene relic macrophyte-dwelling elements. Biodiversity and quantitative characters of the estuarine communities decrease from west to east. Pelophylic detritophages predominated in the benthic communities of the estuary. The results of this research are meant to be used for uncovering historical ways of forming of benthic fauna and clearing up the dependence of community structure on the seawater influence, freshwater flow, regulation of freshwater and seawater sources, nature of changing of faunas at salinization of estuaries connected with the sea and the river network by the system of channels.

Main conclusions. Major factors effecting composition, structure and distribution of benthic communities in the Beysug Estuary are: 1) bottom sediments’ structure (mostly clayey silts of pelite and, in certain parts, alevropelite fractions; 2) bathymetry of the water body (70 % of the estuary presented by 0,6–1 m depths, southern part of the estuary up to 2 m); 3) salinity, which varies from 6 ‰ in the east up to 10 ‰ in the west; 4) presence of macrophytes, solitarily occurring in the western part of the estuary.