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The species composition and distribution of hydropolyps (Hydrozoa) in the Barents Sea and the adjacent section of the Norwegian Sea based on the results of samples from expeditions of PINRO in 2003–2008

In this work we reported data on the biodiversity, distribution, and biogeographic composition of the Hydrozoa fauna of the Barents Sea. The analysis used materials collected in the Barents Sea on expeditions from 2003 to 2008. Totally 78 species of hydropolyps belonging to 37 genera, 16 families and 3 orders were found. But 7 species had been found in more than 10% of all stations and formed about 75% of the total biomass. According to biogeographic characteristics, they can be combined into 6 large groups, but the basis of the Hydrozoa fauna was consisted by boreal-arctic and boreal species entering the Arctic. The richest species diversity was found in the fauna of the southwestern, northwestern, and southeastern regions, and the poorest in the northeastern region. Theoretically, the limiting number of hydroid species living in the Barents Sea can reach ~ 130. Hydropolyps are not evenly distributed across the sea, depending on a number of abiotic factors. As was shown by the results of constructing multiple regression, the greatest influence on the hydroid biodiversity was exerted by depth, degree of siltation of bottom sediments, temperature of the bottom layer of water, gravel and coarse fractions in sediments, and gradient of the bottom slope. Biomass indicators depended on depth, degree of siltation of sediments and gravel and larger fractions.