Shell-bearing Gastropoda from the methane seeps and hydrothermal vents of the Bering Sea: A preliminary description

The first description of the fauna of shell-bearing gastropod from chemosynthesis-based communities of the Bering Sea is given. The work includes materials collected during the cruises of the RV Akademik M.A. Lavrentyev in 2016 and 2018 in two types of the reducing biotopes: hydrothermal fields on the underwater Piip Volcano and the methane seeps on the Koryak slope of the Bering Sea. The Piip Volcano (similar to 368-495 m) is the northernmost (55 degrees 22' - 55 degrees 24' N) hydrothermal region in the Pacific. Methane seep fields of the Koryak slope found between 400 and 700 m depth are the northernmost chemosynthesis-based habitats known to date in the Pacific (60 degrees 49-61 degrees 10). In total, 27 recognizible taxonomic units (RTUs) of shell-bearing gastropods were identified from both areas, at least six of them presumably belong to species new to science. Also, five species are new to the fauna of the Bering Sea and adjacent areas of the Pacific Ocean. Only nine RTUs were found on the Piip Volcano, among which there was one species, Provanna sp. nov., belonging to the family known only from chemosynthesis-based communities and another species, Parvaplustrim wareni, was potentially obligate for chemosynthesis-based communities. Nineteen RTUs have been identified in the methane seeps of the Koryak slope, however no taxa specific for chemosynthesis-based communities had been recorded. Gastropods have less aggregated population structure on the Koryak slope than on the Piip Volcano, where four times as many specimens have been collected. In general, the pattern of distribution of taxonomic and functional groups in the area of methane seeps of the Koryak slope is presumably the same as in the background communities while in the hydrothermal zone of the Piip Volcano it is similar to other types of extreme communities. Majority of gastropods from both regions feed on detritus or invertebrates. Most RTUs have a lecitothropic protoconch, which corresponds to a short period or absence of pelagic stage in their development. This makes the species associations of gastropods vulnerable.