March 2025
There was one thing the field team immediately agreed upon: This was not your average vessel.
The first thing we noticed when pulling into Port Fourchon, Louisiana, was the sheer size of the M/V Island Intervention—it stretched the entire length of the dock, making it impossible to fit the whole thing in the frame of a smartphone camera. The ship measured at just under 400 feet long—slightly larger than a football field—and could carry 130 people aboard. The larger of its two massive deck cranes was already at work, lifting hundreds of thousands of pounds of equipment from the dock to the aft (back) deck of the ship. There was an excited, and slightly nervous, energy in the air as the crew called back and forth, making sure we had everything we needed for the weeks ahead.
The anticipation was palpable, and rightfully so. Partners from NOAA, the United States Geological Survey (USGS), the U.S. Navy, Smithsonian National Museum of Natural History, Audubon Aquarium, and more had traveled from all over the country to convene on the ship. This mission was years in the making, representing a major NOAA-Navy collaboration in the region, and one of only a handful of times saturation divers supported a NOAA mission. Everyone was acutely aware of how important—and ambitious—the goals were for the next few weeks.
The ship served as an easy metaphor for the mission itself—it was big, had a lot of moving parts, and required an experienced team to run it. After years of planning, we were finally here, and ready to get to work.
Restoration in the Wake of Tragedy
This expedition was one of 14 in 2024 to support the Mesophotic and Deep Benthic Communities projects, implemented to help restore deep-sea habitats injured by the 2010 Deepwater Horizon (DWH) oil spill in the Gulf of America (formerly the Gulf of Mexico). The spill, started by an explosion that killed 11 people on a drilling platform less than 50 miles from the coast of Louisiana, resulted from a catastrophic leak from the oil well. It remains the largest offshore oil spill in U.S. history, with about 134 million gallons of oil spilled over almost three months.
When most people think of the spill, they picture the shiny slick on the water’s surface or black globs of oil washing up on beaches. Some of the oil, however, never made it off the seafloor—more than 770 square miles of deep-sea habitat, an area more than half the size of Rhode Island, were injured by the spill. These mesophotic and deep benthic habitats, or areas of the seafloor that see little to no sunlight, are vast and complex ecosystems that serve as the foundation of food webs in the region. Although it was clear they needed to be restored following the spill, this wasn’t an easy task—they were hard to reach and there was still much we didn’t understand about these habitats.
After the DWH oil spill, federal and state agencies formed the Deepwater Horizon Natural Resource Damage Assessment Trustee Council (DWH Trustees) to assess the impacts and identify and implement actions to restore injured habitats, species, and the services they provide. In 2019, the DWH Trustees for the Open Ocean Restoration Area selected four projects to restore Mesophotic and Deep Benthic Communities (MDBC)—focused on mapping and habitat modeling, coral propagation, habitat assessment, and active management. Led by NOAA and the Department of Interior, these projects further our understanding of mesophotic and deep benthic habitats so we can ensure their resiliency in the face of a changing ocean. Since 2021, the MDBC team has conducted expeditions at sea to complete crucial field work in support of restoration activities.
An Extensive Restoration Toolbox
That hot summer day in Port Fourchon marked the start of a 19-day expedition to advance the MDBC restoration projects at a few target sites offshore from Texas and Louisiana, including within Flower Garden Banks National Marine Sanctuary. Although the DWH Trustees didn’t document any evidence of exposure to DWH oil or dispersants within the sanctuary, long-term monitoring studies in the protected area have provided crucial data to support MDBC restoration throughout the region. By understanding healthy habitats unaffected by the oil spill—like those within the sanctuary—experts can more effectively implement restoration and evaluate progress in impacted areas.
Working on a ship as large and advanced as the M/V Island Intervention presented a unique opportunity to apply many restoration tools at once. A remotely operated vehicle (ROV) was deployed throughout the day and night to conduct video transects, install coral propagation experiments, and place benthic landers to monitor conditions on the seafloor. Meanwhile, a team of saturation divers from the U.S. Navy Experimental Dive Unit collected biological samples, speared invasive lionfish, rigged large marine debris for removal, and installed equipment for mooring buoys. These divers lived for up to a week in a tube-shaped “saturation” habitat on the back deck, which kept their bodies at the same pressure as their worksite on the bottom, allowing them to go far beyond recreational diving limits, stay at depth longer, and accomplish more work in less time than if they were returning to the surface after each dive.
A dive support team monitored the divers continuously while they were under pressure to make sure there were no concerns. Inside the ship, data managers kept watch 24 hours a day, diligently tracking every piece of equipment deployed and every sample collected. Whenever the ROV or divers returned to the surface, there was a flurry of activity as members of the science team rushed to process biological or sediment samples in the labs on the back deck. There was rarely down time—the team was determined to make use of every single minute of ship time.
Collaboration Within the Sanctuary
Throughout the planning process and expedition, the team worked extensively with Flower Garden Banks National Marine Sanctuary staff to restore mesophotic habitats within the sanctuary boundaries that are vulnerable to impacts. One of the primary goals they identified was to install new mooring buoys that would reduce the threat of damage from anchoring in mesophotic habitats, while also allowing easier access for guests visiting the sanctuary and staff monitoring the health of the habitat. Sanctuary staff worked for months leading up to the mission to design and build buoys that could withstand the stress of the mesophotic depths. Using the ROV, saturation divers, and topside crane operations, the team deployed six of these newly designed mooring buoys, greatly expanding access in hard-to-reach parts of the sanctuary.
Another goal was to remove threats along the seabed. Using previously collected data from monitoring expeditions in the sanctuary, the MDBC team identified large pieces of marine debris that posed a potential threat to habitats if they were to move or become dislodged during a storm. One of the targets, a monitoring buoy, was lost during a hurricane in 2003 and weighed almost two tons—staff feared it could be dislodged in a future hurricane, causing damage to seafloor habitats. After a scouting dive by the saturation divers to make sure it was safe to place lifting straps under the buoy and remove it, the ROV and crane operators worked together to pull the buoy to the surface. In addition to removing the threat from the seafloor, scientists were able to collect 100 biological samples from the buoy for further analysis. Over the course of the expedition, the team removed 15 items of debris from mesophotic habitats, totaling more than 2,500 pounds.
Debris wasn’t the only threat identified in the sanctuary—saturation divers also removed invasive lionfish. Originally from the Indo-Pacific region, lionfish were first observed in the sanctuary in 2011 and pose a potential threat to native fish. The Navy saturation divers were equipped with pole spears and collection tubes to remove lionfish while protecting themselves from the fishes’ venomous spines. They collected almost 40 fish between 173 and 328 feet deep, and scientists on deck quickly took samples to look at genetics, the presence of mercury and an illness-causing toxin called ciguatoxin, and stable isotopes (tells us which types of food the lionfish are eating). One lionfish dissection was even filmed and broadcast through a livestream on Youtube, allowing people a chance to ask questions and view on-board activities firsthand. It was one of six public livestreams aboard this expedition, all of which are still available for viewing.
A Successful Mission
Ultimately, years of planning resulted in a successful restoration mission. In just under three weeks, the ROV collected about 300 hours of footage across 80 dives and saturation divers accrued 60 hours of operational bottom time. Scientists collected almost 300 genetic samples and out-planted nearly 60 coral fragments to study their growth over time. Thousands of people got a first-hand view of ship activities through livestreams, and coral samples collected from the mission are currently on display at the Audubon Aquarium.
The expedition was a shining example of how experts from across civilian and military federal agencies, academia, industry, and the nonprofit sector can combine resources to advance restoration goals. The work is just beginning, however. It will take years to realize all the outcomes of this and other expeditions from the 2024 field season. As we speak, team members are hard at work analyzing ROV footage, performing genetic analyses of biological samples, processing sediment cores, and more. The mission helped protect mesophotic communities within the sanctuary and expand our knowledge in ways that will help us restore them throughout the region. But, we’re not done yet—the 2025 field season starts in just a few months, and there is a lot of restoration work left to do.
Erin Spencer, PhD, is the communications manager for the Mesophotic and Deep Benthic Communities portfolio
Rachel Plunkett is the content manager and senior writer/editor for NOAA’s Office of National Marine Sanctuaries