The deep NW Pacific has been intensively analyzed in the last decade, during an international collaboration between German and Russian scientists, which has resulted in a vast, unique collection of material from previously unexplored areas. Until now, the environmental forces that could be driving species richness patterns in the deep NW Pacific have not been explored widely. Therefore, in this paper, we utilize new species distribution data from four deep-sea expeditions to the NW Pacific (2010–2016), which include the Sea of Japan, Sea of Okhotsk, the abyssal plain adjacent to the Kuril-Kamchatka Trench (KKT) and the KKT, to better understand species connectivity, biodiversity patterns, and distribution ranges in deep-sea benthos in this region. To determine the best environmental predictors driving these deep-sea species richness patterns, we applied generalized additive (GAMs) and linear models (GLMs). We calculated the total number of geographic distribution records, alpha (total number of species per 10,000 km2 hexagonal cells) and gamma species richness (total number of species per 1° latitudinal bands), and expected number of species (rarefaction ES15). Our highest number of distribution records and gamma species richness during the last decade peaked at intermediate latitudes (42°−44°N) along the mesopelagic zone (500–1000 m) of the Sea of Japan and abyssopelagic zone (4000–6000 m) of the NW Pacific and KKT. When sampling bias was accounted for, the alpha species richness in bathypelagic zone (1000–4000 m) of Sea of Okhotsk and abyssopelagic zone (4000–6000 m) of the NW Pacific and KKT were as high as mesopelagic zone of the Sea of Japan. The similarity cluster analysis of species presence/absence in lower bathyal/hadal (3000–8500 m) revealed three distinct geographic regions including Sea of Japan, Sea of Okhotsk, and KKT in the NW Pacific. The eastern sector of the Sea of Okhotsk and western KKT had c. 50% of species in common. Several species of deep-sea Bivalves, such as Dacrydium rostriferum and Vesicomya pacifica, had the greatest latitudinal distribution ranges among all species. Echinoderm Ophiura leptoctenia, had instead, the broadest bathymetric distribution ranges compared to all other collected species. GAM models indicated that dissolved oxygen was the best explanatory variable for predicting numbers of species, closely followed by the model including all environmental variables plus topography. However, the GLM models of species richness, with latitudinal intervals of 1° and 5°, found that the topography and temperature were the best predictors of number of species. GLM model outputs indicated that a model that contains only the number of distribution records is, for all practical purposes, as good as any model that contains an environmental predictor. This study provides new insights on the NW Pacific deep-sea species richness patterns, where dissolved oxygen might play an important role, especially when considering the Oxygen Minimum Zones (OMZs) in the deep NW Pacific. |
