Upper Bathyal Pacific Ocean biogeographic provinces from octocoral distributions

Abstract

Abstract Biogeographical classification schemes such as the Marine Ecoregions of the World (MEOW) have been developed for continental shelf depths. The lack of faunal data in the deep sea has led to the development of biogeographical units based on oceanographic characteristics. The aim of this study was to propose biogeographical schemes for the Upper Bathyal (200–1000\xa0m) across the Pacific Ocean using octocoral distributions. We retrieved over 200 000 octocoral data records from the Deep Sea Coral Data Portal (DSCDP), Ocean Biogeographic Information System (OBIS), Tropical Deep-Sea Benthos program (French National Museum of Natural History), Queensland Museum from the CIDARIS expeditions, and records retrieved from the Siboga expedition reports. We used cluster analysis to examine octocoral distributions against four different biogeographical classification schemes. The classification schemes produced mostly concordant patterns with three major faunal distribution barriers: the North Pacific Current isolates the subarctic units by creating a steep temperature gradient; the Subantarctic Front separates the Subantarctic from the rest of the Pacific; and the East Pacific Barrier separates the East Pacific from the Central and West Pacific. Two other smaller but distinct provinces are the Indo-Pacific where Lower Bathyal genera are found in the Upper Bathyal, and Torres Strait/Coral Sea characterised by mesophotic genera. We propose 12 biogeographic provinces across the Pacific Ocean Upper Bathyal region from 200 to 1000\xa0m depth based on octocoral distributions. The main driver for these units seems to be temperature, a defining feature of water masses. These units could potentially be subdivided into smaller regions based on habitat. Additionally, the clustering of Ecological Marine Units (EMUs) provides evidence that the Upper Bathyal should in certain regions be divided vertically into two depth zones based on water masses.