The ecology of deep-sea coral and sponge habitats of the central Aleutian Islands of Alaska

The first in situ exploration of deep-sea coral habitat in the central Aleutian Islands in 2002 confirmed expectations that had been based on fishery bycatch and research survey records which indicate corals are widespread, diverse, and abundant. This paper reports observations from analysis of video collected during 2003 and 2004 in a study area that expanded the range of earlier observations to depths beyond current fishing activities (~1000 m) and encompassed the entire central Aleutian Island region. Video of the seafloor was collected at 17 sites with a manned submersible to depths of 365 m and a remotely operated vehicle to 2947 m. Corals, sponges, and other emergent epifauna were widely distributed throughout the study area and present at all depths. Changes in density and species richness were observed at depths of 400–700 m, with abundance and diversity increasing as depth decreased. The distribution of individual fishes, crabs, and octopods was examined relative to emergent epifauna: 63% of the fishes, crabs, and octopods were found in the same sampled video frames as were corals, 69% of them were found in the same frames with sponges, and 55% of them were found in the same frames with “other” emergent epifauna. Most species at depths <1000 m were observed near emergent epifauna, and evidence indicates that epifauna may be essential to some taxa. The extensive closures implemented in 2006 as part of the Aleutian Islands Habitat Conservation Area provide important protection to much coral and sponge habitat that may serve as a source of recruits to nearby disturbed habitats, but observations made during this study indicate that the majority of garden habitat in the study area may currently remain open to bottom trawling.