Composition and distribution of polychaete assemblages associated with hydrothermal vents and cold seeps in the Bering Sea

Abstract

Two areas with reducing habitats in the western Bering Sea were investigated during two expeditions onboard the RV Akademik M.A. Lavrentyev in 2016 and 2018. Hydrothermal vents of the Piip submarine volcano, located in the southwestern Bering Sea, and methane seep communities recently discovered on the Koryak slope in the northwestern Bering Sea were surveyed using a ROV Comanche 18. Species composition and distribution of polychaete (Annelida) assemblages of hydrothermal vents, cold seeps, and background sediments from the studied areas were investigated. A total of 47 species and 20 families were identified from the Piip volcano. In the area of methane emission on the Koryak slope, 86 species belonging to 32 families were collected from five separate fields at depths from 400 to 700 m. Considerable differences in structure and composition were revealed between seep polychaete assemblages, as well as between polychaete assemblages of the vent, seep, and background habitats, which showed different abundance and species richness values, sets of dominant species, and taxonomic compositions of species specific to vents and seeps. Elevated abundance and species richness values, as well as a higher diversity of the vent and seep-associated polychaete assemblages compared to the surrounding seafloor were found in vesicomyid Calyptogena pacifica beds. In contrast, the vent and seep polychaete assemblages associated with microbial mats showed a poorer family and species composition, and had a lower abundance, species richness, and diversity compared to the surrounding benthos. The variations observed in the structure and composition of polychaete assemblages are apparently associated with geochemical local conditions due to changes in intensity of toxic vent fluids and seepage emissions. The similarity between the vent and seep faunas of the studied areas of the Bering Sea was found to be low, which suggests the existence of distinct assemblages inhabiting reducing ecosystems. In addition, the higher similarity between the vent and seep polychaete assemblages was associated with vesicomyid bivalve beds. The dissimilarities between the vent and seep polychaete assemblages were mainly due to the different sets of vent- or seep-specific species.