Forests of the Deep: High-density deep-sea coral and sponge communities in the Central and Western Pacific

High-density coral and sponge communities represent hot-spots of biodiversity in the deep sea. Based on their functional role as habitat and their fragility, such communities have been recognized as priorities for conservation, both within U.S. waters and internationally – often classed as ecologically and biologically significant marine areas and vulnerable marine ecosystems. Discovering and characterizing these communities on seamounts and island slopes in the Central and Western Pacific was a major focus of the National Oceanic and Atmospheric Administration (NOAA) Campaign to Address Pacific monument Science, Technology, and Ocean NEeds (CAPSTONE). This 3-year campaign explored deepwater habitats around U.S. Pacific Islands aboard the NOAA Ship Okeanos Explorer, representing one of the most ambitious U.S. deep sea exploration efforts. Surveys conducted during 168 remotely-operated vehicle (ROV) dives discovered 44 high-density (>3,000 corals and sponges/km) and 12 very high-density (>10,000/km) communities at depths from 250 m to 2800 m. While there is clear differentiation among assemblages at different depths or temperatures, there was a significant amount of additional variation that was likely based on other factors. We will present a preliminary characterization of these important deep-sea communities, including an analysis of their structure and association with island and seamount geomorphology. We will also discuss the implications of our findings for their conservation, particularly in light of the potential development of commercial deep-sea mining in the region.