Deep-Sea Coral Abundance, Distribution, and Community Structure on Seafloor Features Across a Broad Depth Gradient in North-Central California National Marine Sanctuaries

Patterns in deep-sea coral (DSC) diversity and distribution are described for a range of benthic habitat features including offshore banks, continental shelf and slope, and submarine canyons in three national marine sanctuaries off the coast of North-central California. Sixteen visual datasets of DSC observations collected using underwater vehicles from 2010 to 2021 across a wide depth range of 35–3317 m were analyzed for zonation by depth and seafloor feature type. A total of 36,670 DSC from at least 20 families were documented in the study area. Taxa displayed patterns corresponding to depth and seafloor feature type, such as broad distribution across multiple depths and features or narrower depth range and fewer features. Significant divergence in DSC assemblage diversity and density occurred between banks and canyons, representing the shallowest and deepest depth extents in the study area. One species of Stylasteridae coral primarily inhabited banks and accounted for the highest density of all DSC taxa. Diversity of soft corals and gorgonians (Octocorallia) and black corals (Antipatharia) was greatest on the slope and canyons. Other octocorals such as sea pens (Pennatuloidea) collectively spanned the largest depth ranges throughout the study area on all features other than banks. Comprehensively describing DSC communities in relation to seafloor features throughout an extensive depth range may have applications to other regions globally where similar habitats and DSC families are found. Our growing understanding of taxonomic diversity and zonation adds to existing knowledge of depth and geographic distributions on the U.S. West Coast and provides a crucial foundation for effective management and conservation efforts for DSC communities.