Diversity and Environmental Drivers of Deep-Sea Sponge and Coral Communities in Alaska

The U.S. North Pacific harbors some of the densest and most diverse cold-water coral and sponge communities globally, yet quantitative data for depths below 900 m in the Gulf of Alaska and Aleutian Islands remain scarce. Most records originate from <300 m, despite ∼80% of Alaska’s seafloor exceeding 200 m depth. Using Remotely Operated Vehicle video imagery from two NOAA Ocean Exploration expeditions in 2023 (Seascape Alaska 3 and 5), we conducted a quantitative, image-based assessment of deep-sea coral and sponge communities across 15 previously unvisited sites spanning 380-3,200 m depth. From 15,531 observations, we documented 164 distinct morphotypes - 90 Porifera and 74 Cnidaria - substantially extending known distributions for multiple taxa, including five sponge genera new to Alaska and the northernmost Pacific record of the coral genus Umbellapathes . Density and diversity peaked along the margins of the Oxygen Minimum Zone (∼500-1,800 m; O 2 ≤1.43 mg L -1 ). Additionally, eight high-density aggregations were identified using quantitative spatial criteria, reaching densities up to 20.68 individuals m -2 . Community composition was structured by a hierarchy of drivers, with oceanographic setting explaining most variation. These findings highlight the importance of oceanographic context in structuring deep-sea biodiversity and provide a baseline for future ecological, taxonomic, and conservation research in North Pacific deep-sea ecosystems. Understanding the distribution and drivers of cold-water coral and sponge communities is vital for anticipating ecosystem responses to future ocean scenarios and for designing effective management strategies to safeguard these vulnerable deep-sea habitats. • Quantitative assessment of deep-sea corals and sponges across 380-3,200 m in Alaska • Fifteen previously unvisited sites surveyed using NOAA Ocean Exploration data • Eight high-density VME habitats identified using quantitative spatial criteria • OMZ drives abundance peaks while oceanographic regimes structure communities