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Foraminifera g. sp. Hauerinidae g. sp. Porifera Porifera g. sp. Cnidaria Anthozoa g. sp. Actiniaria g. sp. Hydrozoa g. sp. Nemertea Nemertea g. sp. Nematoda Nematoda g. sp. Cephalorhyncha Priapulus caudatus Lam., 1816 Priapulidae g. sp. Annelida Polychaeta g. sp. Spiochaetopterus typicus M Sars, 1856 Maldane sarsi Malmgren, 1865 Maldanidae g. sp. Orbiniidae g. sp. Lumbrineridae g. sp. Lumbrineris sp. Aglaophamus sp. Nephtyidae g. sp. Nephtys sp. Harmothoe sp. Polynoidae g. sp. Galathowenia oculata (Zachs, 1923) Myriochele heeri Malmgren, 1867 Owenia fusiformis Delle Chiaje, 1844 Myriochele sp. Owenia sp. Oweniidae g. sp. Chone sp. Ampharete borealis (M. Sars, 1856) Ampharete sp. Ampharetidae g. sp. Melinna sp. Cirratulidae g. sp. Brada sp. Flabelligeridae g. sp. Cistenides hyperborea Malmgren, 1866 Pectinaria sp. Terebellidae g. sp. Sipuncula Sipunculidea g. sp. Arthropoda Crustacea g. sp. Calanus finmarchicus (Gunnerus, 1770) Calanus sp. Copepoda g. sp. Amphipoda g. sp.

The results of the long-term megabenthos observation program of the Barents Sea and adjacent waters, implemented by Russia and Norway since 2005, are presented. Megabentos is one of the most important parts of the bottom component of Barents Sea ecosystem, forming a significant proportion of living matter included in food chains and the system of ecological relationships. In particular, megabenthic organisms play a significant, and often decisive, role in the nutrition of bottom fishes and crustaceans in the Barents Sea, including the most important commercial species: cod, haddock, Kamchatka crab, opilio crab, etc. Representatives of this group often form specific biotopes that determine the conditions for the existence of many other animal species. The gradual accumulation of knowledge on megabenthos may make it possible to assess its role in the ecosystem and ultimately contribute to a more rational management of Barents Sea resources. The main goal of our research is to identify the spatial patterns and to reveal megabenthos biomass and production dynamics in the Barents Sea. Since 2005, as a part of the assessment of commercial fish and invertebrates’ stocks, megabenthos by-catch from bottom hauls has been processed. This work represents data from 5016 stations (2005–2017), with 238.4 tons of total sampled biomass and 14.9 million individual organisms. The sampling equipment used was a Campelen 1800 bottom trawl – a low-selective active net fishing gear, made of nylon; it was rigged with rockhopper ground gear. For the convenience of the comparative analysis, the quantitative parameters presented in the article were calculated on a standard trawling distance of 1 nautical mile (nm). The processing of the biological material was conducted in accordance with standardized procedures, following the retrieval of each trawl. In total, 694 megabenthic species (1058 taxa) have been recorded, with the greatest diversity observed in the depth range of 100–400 m and the largest mean values of biomass and abundance noted between depths of 600–800 m. The biomass (B) and production (P) values of the benthic megafauna were approximately stable during 9 years of investigation; after 2014, a decreasing trend is observed. The annual production P/B ratio of megabenthos was calculated to be at 0.3. Distribution, contribution to production, and gross biomass values of at least 694 megabenthic species had been underestimated in the previous studies of Barents Sea benthos. The dynamics of the mean biogeographical index (the border between areas of the dominance of boreal and Arctic species) within the central-southern part of the Barents Sea suggests that a large part of the area can be characterized as predominantly boreal intermediate since 2013.

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