Diversity and distribution of peracarid crustaceans (Malacostraca) from the continental slope and the deep-sea basin of the Sea of Japan

During the expedition SoJaBio (Sea of Japan Biodiversity studies) a rich collection of peracarid crustaceans from the slope and the deep-sea basin of the Sea of Japan (at depth range from 450 to 3660 m) was made. The superorder Peracarida was recognized as the most abundant taxon of the macrobenthos in the investigated area and comprised 146 species, 85 genera, 42 families and five orders. From these taxa 93 species, 18 genera and 10 families are reported for the first time in the Sea of Japan below 500 m. Among them, 42 species and two genera were apparently new to science. The diversity and species richness as well as abundance of most of the peracarid species were highest at the shallowest slope stations (∼ 450–550 m) and decreased with depth. Conversely, the abundance of three species, Eurycope spinifrons Gurjanova, 1933 (Isopoda), Chauliopleona hansknechti Larsen et Shimomura, 2007 and Paratyphlotanais japonicus Kudinova-Pasternak, 1984 (Tanaidacea) increased distinctly below the slope (∼2600–3300 m). It is assumed that these species are opportunistic taxa which have recently colonized the geologically young pseudo-abyssal habitats of the Sea of Japan. On the basis of faunistic similarity between 24 stations, three distinct faunal assemblages were identified, distributed on the slope (∼450–1500 m), lower slope (∼2500–2700 m) and at the pseudo-abyssal stations. The key peracarid species for each of them were determined.