Six dives in the Cordell Bank National Marine Sanctuary have shed light on deep-sea diversity off Marin’s shores, including a new sponge species and the first observations of many corals in the sanctuary.
Between 2017 and 2019, the National Oceanic and Atmospheric Administration and the Ocean Exploration Trust collaborated on the first video surveys of deep-sea canyons and slopes off Cordell Bank. Surveys were taken from the E/V Nautilus, a 210-foot research vessel equipped with the remotely operated vehicle Hercules.
Hercules allowed the team to record observations in unexplored deep-water coral reef environments like Bodega Canyon, a large seafloor feature more than 12 miles long and over 6,500 feet deep. These were the deepest dives ever made in the sanctuary, half of which has yet to be explored.
“Before these two cruises, we’d never been to these depths,” said Dani Lipski, a research coordinator at Cordell Bank and the lead scientist for the site. “We’re seeing broad categories of species that have never been recorded in the sanctuary before.”
Ecosystems in the ocean are structured by depth, and the regions that surround Cordell Bank are suitable habitat for deep-sea corals and sponges. “When you drive out to the Sierra, you see the ecosystems change with elevation. It’s the same thing in the deep sea,” Ms. Lipski said.
At least 15 sponges were observed for the first time on the Nautilus dives, and one is an entirely new species, dubbed Farrea cordelli. The delicately featured, ruffled white sponge was collected in Box Canyon at a depth of nearly 7,000 feet.
Sponges can be challenging to identify, and not all specimens collected on the dives have been described. Dr. Henry Reiswig, a sponge expert with the Royal British Columbia Museum, died shortly after describing the Farrea cordelli. “It’s tragic we’ve lost him as a resource because there are not a lot of people practiced at the art of sponge taxonomy,” said Kaitlin Graiff, a research contractor with Cordell Bank.
One large mushroom-shaped sponge about three feet tall was recorded in Cordell Bank for the first time in 2019 and is thought to range as far north as the Aleutian Islands. “When I saw this sponge, I was so excited I nearly jumped out of my chair, but with the loss of Henry we don’t have anyone to identify it yet,” said Ms. Graiff, who was tasked with combing through hundreds of hours of video from the Nautilus surveys.
Besides sponges, deep-sea corals collected on the dives are of particular interest to scientists because they are long lived, slow growing and provide habitat for a huge variety of organisms. “They’re almost like a condominium for other animals,” Ms. Graiff said. “We saw eggs and invertebrates like brittle stars and crabs.”
Of the 38 coral species observed, 31 were previously unknown to live in the sanctuary. The corkscrew coral, Radicipes stonei, had previously been found only at two locations in the Aleutian Islands, and Isidella tentaculum and Keratosis sp., long-lived bamboo corals greater than two meters in diameter, were aged up to 400 years old. Bamboo coral, almost like a tree, lays down rings as it grows, and as it ages it keeps a signature of environmental conditions in its rings, much like a tree.
Deep-sea corals and sponges are thought to play an important role in the carbon cycle. They are filter feeders attached to hard seafloor features and catch floating “marine snow” that drifts from surface waters to the seafloor. Corals may also provide refuge for the larvae of commercially important fish species. Like their warm-water cousins, deep-sea corals’ skeletons are made up of colonies of small animals. These corals can live for hundreds to thousands of years in cold, dark waters 200 to 20,000 feet below the surface.
The community of researchers identifying deep-sea animals is small, and much is still unknown about the ecological function of creatures like corals and sponges. Observation data from the Nautilus dives will be shared with taxonomy libraries and databases for a better understanding of deep-sea habitats, Ms. Graiff said.
Footage of the Nautilus surveys can be found at www.nautiluslive.org.