Bivalve molluscs of the abyssal zone of the Sea of Okhotsk: Species composition, taxonomic remarks, and comparison with the abyssal fauna of the Pacific Ocean

摘要

SokhoBio expedition Until recently hardly anything was known about the abyssal bivalve fauna of the Sea of Okhotsk, which communicates with the Pacific Ocean via many straits between the Kuril Islands with a maximum depth of 2318 m in Bussol Strait, and about its similarity with the deep-water fauna of the Pacific. Investigation of the materials collected by the SokhoBio Russian-German deep-sea expedition (RV "Akademik M.A. Lavrentyev", 2015), and two Russian expeditions (RV "Toporok", 1948; RV "Vityaz", 1949) from the bottom of the Kuril Basin of the Sea of Okhotsk (2850-3366 m depth) revealed a rich fauna of bivalves including 25 species belonging to 12 families, of which only 12 species (48.0%) were determined to the species level. Nine species (Poroleda extenuata, Katadesmia vincula, Dacrydium rostriferum, Bathyarca imitata, Catillopecten squami-formis, Channelaxinus excavata, Vesicomya pacifica, Cuspidaria cf. abyssopacifica, Myonera garretti) were first records for the Sea of Okhotsk. The richest families were Thyasiridae (7 species) and Cuspidariidae (6 species). The high diversity and richness of the bivalve fauna on the bottom of the Kuril Basin are probably caused by the favorable trophic conditions. The Kuril Basin is characterized by very high rates of sedimentation and high content of organic matter in the sediments. For estimation of connections between deep-water faunas of the Sea of Okhotsk and the Pacific Ocean, the SokhoBio expedition performed 1 station at the maximum depth of the Bussol Strait and 2 stations (3342-3432 and 4679-5013 m) on the Pacific slope of the Kuril Islands opposite to the Bussol Strait, where 24 species belonging to 13 families were found. Among the 25 species found in the deep part of the Kuril Basin more than half of species (17 species, 68%) occur in the Pacific Ocean. Most of them are widespread in the northern Pacific and are eurybathic bathyal-abyssal species. This probably allows them to penetrate into the Sea of Okhotsk through deep straits between the Kuril Islands. Photographs and taxonomic remarks are provided for all identified species (15) that were found in the Sea of Okhotsk and/or the Pacific Ocean. Taxonomic decisions herein: Nuculana aikawai Habe, 1958 and Nuculana sagamiensis Okutani, 1962 are synonymized with Nuculana leonina (Dall, 1896); Arca (Bathyarca) nucleator Dall, 1908 is synonymized with Bathyarca imitata (Smith, 1885); for Leda extenuata Dall, 1897, a new combination is suggested, Poroleda extenuata (Dall, 1897).