Fathoming the Deep: Increasing Our Understanding of Deep-Sea Ecosystems In West Coast Sanctuaries

In collaboration with Oregon State University, OET, and Olympic Coast National Marine Sanctuary, researchers conducted nine deep-sea ROV dives during an expedition to investigate seafloor habitats featuring methane seeps and hydrates, and deep-sea corals and sponges. These habitats were often found in close proximity to each other, hinting at the ways in which these productive seafloor systems interact to sustain living marine resources and contribute to ‘essential fish habitat.’ During the expedition, viewers were treated to stunning visuals of rarely seen deep-sea communities including exquisite, robust coral colonies and a variety of different sponges – some of which are being evaluated by taxonomists as potential new species.

“Working with OET affords us a rare opportunity to shine a light on the deepest and most remote parts of the sanctuary, and to share this fascinating realm with our local partners, including Washington’s Coastal Treaty Tribes and other rural coastal communities, as well as interested viewers from across the state and around the world,” said Jenny Waddell, research coordinator for Olympic Coast National Marine Sanctuary.

Pioneer Canyon is located in the northern portion of Monterey Bay National Marine Sanctuary and is administered by Greater Farallones National Marine Sanctuary. The head of the canyon is approximately 27 miles west of Half Moon Bay, reaching depths over 1,300 meters (4,265 feet) inside the sanctuary and depths of over 3,000 meters (9,842 feet) outside of the sanctuary. Pioneer Canyon was formed by the outflow of the Sacramento River, when sea level was much lower and the North American Plate was further south. During the expedition, researchers completed two 24-hour dives, revealing a variety of habitats ranging from gently-sloped, soft sediments with sea pens and benthic fish, to steep rocky terrain with numerous bamboo and bubblegum corals, and large delicate glass sponges.

“E/V Nautilus cruises greatly expand our understanding of the diversity and richness of the deep-sea communities in our national marine sanctuaries. The deep waters of the sanctuaries are rarely explored, and the ROV dives reveal many secrets of North America’s most ecologically rich underwater treasures in the San Francisco Bay area”, said Jan Roletto, research coordinator for Greater Farallones National Marine Sanctuary.

Located in Monterey Bay National Marine Sanctuary, Davidson Seamount is an inactive volcanic undersea mountain habitat and is one of the largest known seamounts in U.S. waters. From base to crest, the seamount is 2,280 meters tall (7,500 feet), yet its summit is still 1,250 meters (4,100 feet) below the sea surface. “Davidson Seamount is a very interesting place,” said Chad King, research specialist at Monterey Bay National Marine Sanctuary. He added, “It supports all sorts of life, from massive bubblegum corals and large Picasso sponges, to a colorful and diverse array of marine invertebrates, like sea stars and octopuses.”

Several dives took place at Davidson Seamount during this expedition. The first 22-hour dive characterized approximately 15 acres of seafloor at the top of a small volcanic cone where extensive aggregations of brooding octopus mothers occured. In 10 hours of video footage, 3,647 octopus were counted, 81% of which were brooding mothers. Several hatching events were observed, indicating an important and successful nursery site for this species. In addition to these nursery sites, researchers revisited a whale fall last documented in 2019. To their surprise, the whale fall was more decomposed than expected, but was still flourishing with populations of Osedax and ampharetid worms.

Another successful 18-hour dive was spent in an unexplored region southwest of Davidson Seamount. The seafloor consisted of a variety of basalt formations, including pillow lava, vertical walls, and high rugosity. Corals and sponges across all dives will be identified and counted with video analyses.

Seven dives were completed within Channel Islands National Marine Sanctuary during Nautilus’ 2020 field expedition. The primary objectives of these dives were to conduct visual surveys, characterize deep-sea habitats in unexplored areas, and collect various samples within deep-sea habitats to better understand what influences coral and sponge distributions. In addition to progressing larger, parallel deep-sea research on the West Coast, researchers made a number of interesting discoveries.

In Richardson Rock Marine Reserve, large assemblages of commercially and recreationally important species like vermillion, bocaccio, speckled, and olive rockfishes, were encountered. In deeper areas of the Footprint Marine Reserve, researchers unexpectedly discovered an expansive rolling landscape containing dead glass sponges of the genus Farrea and a diverse, living sponge garden containing high densities of large individuals adjacent to the skeleton mounds. Researchers also confirmed anecdotal evidence of a high abundance of lost fishing gear near the top of Footprint Reef. Regardless if these lines and traps were lost before the implementation of the marine protected area network, or carried into the reserve by currents, marine debris can be harmful to the environment and entangle deep-sea submersibles.

The Santa Lucia Bank, within the proposed Chumash Heritage National Marine Sanctuary, was created by tectonic uplift and is bounded by fault zones to the east and west. Four ROV dives were conducted from E/V Nautilus to visually survey unexplored deeper areas of the bank. Large coral species, including bubblegum corals and primnoids (Parastenella sp.), as well sponge gardens containing numerous large barrel and goiter sponges, were observed for the first time. The deepest dive on the western flank of the Santa Lucia Escarpment yielded soft sediments with patches of hard boulders and ledges, supporting smaller deep-sea species, such as mushroom and black corals, and interesting creatures, including a Grimpoteuthis dumbo octopus, a “purple orb,” later identified as a velutinid snail, and an unusual-looking stalked tunicate (Culeolus sp.).

While most of the world’s deep ocean is still unexplored, the discoveries and data collected during these E/V Nautilus expeditions throughout America’s West Coast sanctuaries illustrate the importance and value of ocean exploration and expand our understanding of the deep sea so we can better manage and protect sanctuary resources. We will continue working with OET aboard E/V Nautilus into the future, so stay tuned for updates on 2021 expeditions.

Jen Mendez is a graduate student at the University of California, Irvine and a Virtual Student Federal Service intern for NOAA’s Office of National Marine Sanctuaries.