Under pressure to restore deep-sea corals

by NOAA Fisheries 17 Sep 2024 16:51 BST

NOAA Fisheries and partners conducted a saturation diving mission deep in the Gulf of Mexico to advance our coral restoration efforts. Throughout the mission, the pressure was on in more ways than one—literally and competitively.

For 3 weeks this summer, a team of experts set out on C-Innovation's M/V Island Intervention to support the Mesophotic and Deep Benthic Communities restoration projects. This effort aims torestore vital seafloor habitats damaged by the 2010 Deepwater Horizon oil spill. This operation, which took place within and around the Flower Garden Banks National Marine Sanctuary, involved a unique combination of data collection methods, as well as some competition akin to the 2024 Olympic Games!

The mission objectives were to:

• Install new mooring buoys to prevent anchor damage to the seafloor in the sanctuary
• Collect samples of mesophotic and deep-sea coral species for lab rearing and propagation
• Collect additional biological, sediment, and water samples
• Remove invasive lionfish and large marine debris
• Complete habitat transect surveys
• Execute coral transplants to test propagation and outplanting methods
• Deploy equipment such as benthic landers and Autonomous Reef Monitoring Structures

The Pressure is On—Literally

Working at depth—in this case, several hundred feet below the ocean's surface—takes some unique methodologies. Often, restoration teams deploy specialized equipment such as remotely operated vehicles to collect samples or observations deep in the ocean. In other cases—as with this mission—we also employ some good old-fashioned humans to get the job done.

Due to our specific needs on this expedition, we partnered with saturation divers from the Navy Experimental Diving Unit. These divers are expertly trained to work quickly and nimbly underwater for long periods of time. Saturation diving involves divers being at depth long enough to bring all the body's tissues into equilibrium with the pressures of the compressed breathing gas in their tank. Most recreational and scientific diving requires divers to spend hours decompressing before returning to the surface after each dive. Saturation diving saves time by keeping the divers under pressure the whole time (cue: Freddie Mercury vocals).

This method requires specialized equipment and techniques to get the job done safely. While the divers live on deck between dives like everyone else, they have to stay within a pressurized chamber on board to ensure the pressure in their tissues remains consistent throughout the mission. Then, when it's time to dive, the divers enter a diving bell that is lowered by a crane onboard the ship. Once lowered to the seafloor, the divers step out into the underwater realm and get to work.

A Competitive Edge: Humans Versus Robots

While the humans were our secret weapon on this mission, we also had a remotely operated vehicle, or ROV, to do some of the heavy lifting. This made for some fun Olympic-style competitions between our humans and underwater robots.

At times, the divers and the ROV were working on similar tasks. Differences in their strengths were very noticeable. We present to you: the underwater restoration Olympics. The divers were able to complete coral propagation tasks more quickly and effectively compared to the ROV, while still maintaining safe dive practices. To practice, while still on board the ship, the restoration team raced the ROV to see who could tie the appropriate attachment knots for a mooring ball faster—this win went to the humans.

The divers also excelled at situational awareness. The human eye is still better than most cameras for depth perception, field of view, and dexterity. In this case, cutting small coral fragments off large colonies and preparing those fragments for growth experiments requires coordination not currently present in ROVs. Score two for the humans.

Project chief Andy David recounted the divers' strengths, stating,

"For fine detail work, there is just no substitute for the human hand. The divers' wide field of view and ability to stay oriented are necessary for large-scale coral restoration."

However, humans can only dive so deep, whereas the ROVs shine in extreme depths. While the divers stayed above 400 feet, we sent the ROV down to 5,000 feet—a depth with pressures so extreme that humans couldn't survive! Obviously, the ROV took home the gold in the depth competition. ROVs also have greater endurance than divers, since they are not susceptible to cold or fatigue. Score two for the robots! But our divers stayed safe, warm, and well-rested (so kind of a win for them, too).

Andy also spoke about the strengths and limitations of the robots:

"The ROV worked well beyond our expectations in both vehicle capability and operator expertise. This heavy-duty ROV was remarkably nimble in tight quarters and the pilots quickly adapted to flying profiles the restoration team requested. Their dive duration, depth range, salvage capabilities, and payload capacity were strong points. While the ROV's manipulators, or robotic arms, were extremely capable."

Bringing Home the Gold

One of the main objectives of this mission was to support ongoing collaborative mesophotic and deep-sea coral restoration efforts. Thanks to both the divers and robots, the entire team brought home the gold—among other colors—corals to rear in the laboratory for restoration efforts, that is. These corals will be transferred to facilities at the NOAA Southeast Fisheries Science Center's Galveston laboratory, NOAA's National Centers for Coastal Ocean Science Hollings Marine Laboratory, and the Audubon Aquarium. All in all, the mission:

• Planted 10 coral fragment racks, each of which can hold 14 fragments
• Deployed nine coral settlement arrays
• Removed 41 invasive lionfish
• Removed approximately 1,800 pounds of marine debris
• Deployed five benthic landers to collect environmental data
• Installed six mooring buoys

In addition to those wins, this mission accomplished some other impressive feats, including:

• One of the first significant NOAA-Navy collaborations in the Gulf of Mexico
• Most time at these depths by humans for a NOAA science mission
• The first time a Navy saturation diving system has been used at sea for a NOAA mission

This mission was a huge success in proving the effectiveness of using both saturation divers as well as ROVs to support operations for mesophotic and deep benthic restoration projects. However, there is still more work to be done.

Looking towards the future, Andy added,

"With what we learned this year, we will be able to maximize our future effectiveness by assigning divers and ROVs to their most productive tasks. This will significantly increase our sampling and deployment efforts."

Partnerships and Funding

The Mesophotic and Deep Benthic Communities restoration portfolio is a partnership between several federal agencies. NOAA works alongside the U.S. Geological Survey and the Bureau of Ocean Energy Management, as well as several academic and cooperative institute partners, on this effort. This particular mission could not have been done without support from the U.S. Navy Experimental Diving Unit Saturation Detachment, as well as collaborators from:

• Smithsonian National Museum of Natural History
• University of Rhode Island
• University of North Carolina Wilmington
• Audubon Aquarium
• National Marine Sanctuary Foundation

The Mesophotic and Deep Benthic Communities restoration program provided funding for the vessel, science mission, and saturation diving field costs. The U.S. Navy provided all staff and equipment required for the saturation diving.