LAUSR

Abstract The NW Pacific lies in the most productive, rich, and diverse region of the World Ocean. The NW Pacific includes several shallow-water oceanic islands and deep-sea basins differing in depths, hydrology and isolation. The adjacent Arctic Ocean includes the northern Bering and southern Chukchi Sea, areas of high productivity characterized by short food chains and shallow depths. Despite the NW Pacifics high species richness, characterization of species diversity and species composition in this region remains poorly explored and/or unknown. Here we attempt to discover how geographic boundaries and depth shape current community assemblages in this area by limiting species richness and geographic distribution ranges. All geographic distribution records were extracted from Ocean Biogeographic Information System (OBIS) and Global Biodiversity Information Facility (GBIF). Distribution data were then cleaned, resulting in a final dataset including 324,916 distribution records of 17,414 species ranging from 0 to 10,900 m depth. We calculated the rate of endemicity and alpha species richness per ecoregion. We also showed how species composition and community structure varies between the tropical and temperate NW Pacific and adjacent Arctic Ocean when sampling bias is accounted for using rarefaction. After accounting for sampling bias, the Eastern Philippines had the greatest species richness (for both pelagic and benthic species) in the NW Pacific and its adjacent Arctic Ocean, and the lowest species richness was observed in Papua. Despite the high species richness in the Eastern Philippines, the Yellow Sea and Gulf of Tonkin had the highest benthic species endemicity rates (ca. 70%) and Aleutian Islands had the highest pelagic endemicity rate (ca. 45%) among all other ecoregions. In the NW Pacific, Chordata, Arthropoda, and Mollusca contributed more than 50% to the species composition of the community. In the Arctic Ocean, Arthropoda, Annelida, and Mollusca were the dominant taxa comprising ca. 82% of the species community. Two significantly distinguished clusters (North and South clusters) were identified based on species similarity analysis including ecoregions of the (1) polar Arctic Ocean and temperate North NW Pacific, and (2) tropical and sub-tropical NW Pacific. We also calculated marine species richness hotspots (actual and expected ES50) and centers of endemism in the NW Pacific and adjacent Arctic Ocean. These analyses reveal an opportunity for marine conservation planning effort as reporting species richness and endemicity hotspots could be highly effective in pinpointing and preventing biodiversity loss.