Tracking the Health of Deep-Sea Corals and Sponges: Results from the West Coast Expanding Pacific Research and Exploration of Submerged Systems (EXPRESS) Field Campaign

M. Elizabeth Clarke, NOAA Northwest Fisheries Science Center, Seattle, WA, United States, Abigail Powell, Lynker - Under Contract to NOAA Northwest Fisheries Science Center, Seattle, WA, United States, Jeffrey Anderson, Nature Imagery, OR, United States, Erica Fruh, NOAA Northwest Fisheries Science Center, Newport, OR, United States, Curt Whitmire, NOAA Northwest Fisheries Science Center, Monterey, CA, United States and Melanie Johnson, Lynker - Under Contract to NOAA Northwest Fisheries Science Center, Newport, OR, United States
Corals and sponges play key roles in deep-sea ecosystems including providing habitats for commercial fish species. Understanding their distributions is essential for developing effective management plans but remains challenging. The cost and logistics of carrying out field work mean that most surveys only represent a single snap-shot in time. Shallow coral and sponge assemblages are dynamic and can exhibit long and short-term variability. Despite the relative stability of deep-sea environments, new evidence shows that deep-sea sponge assemblages can also be dynamic which has implications for site-based management strategies. We describe the results of autonomous underwater vehicles surveys at three rocky banks (Daisy and Coquille Banks, OR and Santa Lucia Bank, CA) off the U.S. West Coast. The banks were first surveyed in 2005, just prior to the establishment of regulations to exclude trawling in parts of banks, and then revisited in 2018 as part of an EXPRESS research cruise. Detailed bathymetric maps were produced to guide initial sampling and fish and sessile invertebrate assemblages were compared between the two time periods. In 2005, Daisy Bank had the highest overall coral and sponge densities, followed by Santa Lucia then Coquille Bank. We observed changes between 2005-2018, particularly in the diversity and abundance of sponges present at Daisy Bank. There was a dramatic increase in the number of sponges from 3335 in 2005 to 14836 in 2018. This was due to a shift in sponge assemblage composition with an increase in lyssacine glass sponges at this site. There was also an increase in small live Heterochone sp. observed and decrease in dead Heterochone sp. skeletons. Benthic assemblages at the other two banks were more stable over the same time period. Our results provide a rare opportunity to examine the temporal dynamics of deep-sea benthic assemblages and indicate that large site-specific changes can happen over relatively short time periods.