Patterns and environmental drivers of marine annelid distribution in the Arctic Ocean

The Arctic Ocean (AO) is experiencing declining sea ice extent and thickness and increasing sea surface temperatures, with cascading consequences for the entire ecosystem. Here, we compiled all available occurrence records of marine Annelida from the Ocean Biodiversity Information System (OBIS) and the Global Biodiversity Information Facility (GIF) and analyzed the number of records, the number of species, and expected species richness (ES15 and ES50) in relation to depth, ecoregion, ca. 12,500 km 2 hexagonal cell and associated them with environmental drivers. The dataset encompassed almost 600,000 occurrence records, with over 460,000 records identified to 1,061 species. Bathymetric analysis revealed the highest number of records and species in the upper 500 m. Most species were recorded along the Norwegian coast, the Barents and Beaufort Seas and around Spitzbergen; regions with high sampling effort and major inflows of Atlantic and Pacific water masses. The ES50 analyses suggested the highest diversity in the Barents Sea, followed by the Norwegian Sea, Iceland, West Greenland, Baffin and Hudson Bay, the Beaufort Sea and the Laptev Sea. This challenges the assumption of a monotonic decrease in richness with increasing distance from Oceanic water inflow. Large Marine Ecosystems (LMEs) in the AO are defined by the PAME (Protection of the Arctic Marine Environment) and clustered into six groups based on species richness reflecting differences in hydrography, productivity and sampling bias. Depth was structuring annelid biodiversity in addition to temperature, sea-ice cover, and food and light availability. The central deep basins and shallow regions with heavy ice cover were severely under sampled. The finding here highlights the importance of continued, well-distributed sampling efforts and taxonomic expertise for understanding the Arctic annelid biodiversity and informing future conservation strategies.