The potential effects of substrate type, currents, depth and fishing pressure on distribution, abundance, diversity, and height of cold-water corals and sponges in temperate, marine waters

Deep-sea benthic environments can be home to diverse communities of corals and sponges which are important habitat for marine fishes and invertebrates. From 2010 to 2014, underwater camera surveys in the Aleutian Islands were completed with the objective of evaluating potential effects of substrate type, tidal currents, depth, and fishing pressure on distribution, abundance, diversity, and size of structure-forming invertebrate (SFI) communities. The presence of rocky substrates was associated with higher probability of presence, higher density, and taller SFI. Multivariate analyses showed community structure changed over gradients of substrate, tidal currents, and longitude, with sea whips typically occupying deeper depths and mostly unconsolidated substrates, while other corals were largely found in rocky, shallower areas. These patterns were also reflected in co-occurrence analyses indicating sea whips were negatively associated with other SFI taxa. Most SFI occupied areas of swift tidal currents; however, heights of individual SFI decreased with increasing tidal currents. Coral and sponge densities at some sites in this study exceeded densities reported from other global coral and sponge habitats. Identifying the environmental conditions leading to high-density and high-diversity SFI communities is important for management of fisheries and evaluating potential impacts of climate change in benthic marine ecosystems.