Vertical distribution of megafauna on the Bering Sea slope based on ROV survey.

Video surveys were carried out during the 75th cruise of the RV (June 2016) along the northern slope of the Volcanologists Massif, in the south-western Bering Sea. The seafloor was explored using the ROV . Seven dives were performed in the depth range from 4,278 m to 349 m. Overall, about 180 species of megafauna were recognised. Fifteen types of megafauna communities corresponding to certain depth ranges were distinguished based on the most abundant taxa. Dominance changed with depth in the following order: the holothurian at the maximum depth (4,277-4,278 m); the holothurian at 3,610-2,790 m; the ophiuroid at 3,030-2,910 m; benthic shrimps of the family Crangonidae at 2,910-2,290 m; the holothurian at 2,650-2,290 m; benthic jellyfish from the family Rhopalonematidae at 2,470-2,130 m; the enteropneust Torquaratoridae at 2,290-1,830 m; the holothurian and the ophiuroid of the genera and at 1,830-1,750 m. At depths 1,750-720 m most of the megafauna was associated with live or dead colonies of the sponge spp. Depths 720-390 m were dominated by the coral and/or At 390-350 m depth, the shallowest depth range, the dominant taxon was the zoantharian sp. Soft sediment megafauna communities dominated by torquaratorid enteropneusts to our knowledge have not been observed before in the deep-sea, the same as communities with a dominance of benthopelagic rhopalonematid jellyfish. The depths of the largest community changes, or the largest turnover of dominant species, were revealed at ∼2,790 m between the bathyal and abyssal zones and ∼1,750 m and ∼720 m within the bathyal zone.