Abyssal gastropods in the Sea of Okhotsk (Vetigastropoda and Caenogastropoda)

Abstract The joint Russian–German expedition SokhoBio in 2015, on the research vessel Akademik M.A. Lavrentyev, provided the first opportunity to investigate the richness and composition of the abyssal gastropod fauna in the Kuril Basin of the Sea of Okhotsk, from which only a single species has been recorded in the literature. During the expedition, sampling of benthic animals was conducted at eight stations in the Sea of Okhotsk and at three stations in the Pacific (landward slope of the Kuril–Kamchatka Trench) using an Agassiz trawl, an epibentic sledge, and a giant box corer. A total of 417 specimens of ‘prosobranch’ gastropods were taken alive and were classified into 15 families and 70 species of Vetigastropoda and Caenogastropoda. Both abundance and richness were lower than expected in the Kuril Basin compared to the Pacific: 97 specimens belonging to 27 species (11 families) were collected at seven stations in the Kuril Basin, while 286 specimens in 43 species were found from two abyssal stations on the Pacific side of the Kuril Islands. Only six species occurred at abyssal depths on both sides. Familial composition also differed: large-sized buccinids were common only on the Pacific side. The very low levels of dissolved oxygen might explain the low abundance and richness, as well as the scarcity of large species, of Gastropoda in the Kuril Basin.