Global biogeography of the lower bathyal (700-3000 m) as determined from the distributions of cnidarian anthozoans

The Lower Bathyal (approximately 700-800 to 3000-3500 m depth) of the deep sea, until recently, had only been explored in areas of continental slopes. With the advent of remotely operated vehicles (ROVs), seamounts and ridges, which comprise the bulk of the seafloor at those depths, have been increasingly sampled, at least for megafaunal species. We compiled records of cnidarians obtained from the Ocean Biogeographic Information System (OBIS) along with records of octocorals identified during ROV dives in the NW Atlantic and Central Pacific among other places, and used them to test the validity of the Watling et al. (2013) lower bathyal provinces which were proposed on the basis of hydrography. In addition, all records were used to independently determine the presence of biogeographic provinces using the Infomap Bioregions network analysis approach. Both methods have their shortcomings, but the combined results suggest that most of the provinces proposed by Watling et al. (2013) were reasonably well delineated; some changes were needed, especially in the North Atlantic. Specifically, the North Atlantic province needs to be divided into eastern and western units and the boundaries of the Boreal NW Atlantic (=Northern Atlantic Boreal) should be extended southward. Several name changes for various provinces are also proposed. Apparent endemism for those provinces where sufficient records exist was at least 33%, much higher than the 10% normally used when evaluating shallow water biogeographic provinces.