by Courtney Mattison
Two new studies provide evidence that the Deepwater Horizon oil disaster has harmed coral ecosystems in the Gulf of Mexico’s mesophotic or “twilight” zone along a series of deep-water rocky reefs known as the Pinnacle Trend. Located approximately 200-300 feet below the surface at the edge of the continental shelf of Louisiana, Mississippi and Alabama, this region’s mesophotic (or “middle light”) zone supports vibrant fish, coral and sponge communities in the Gulf.
In their latest study published last month in the journal Coral Reefs, researchers from the National Oceanic and Atmospheric Administration (NOAA), Florida State University, and JHT Inc. compared the health of corals on hard-bottom mesophotic reefs before and after the Deepwater Horizon oil disaster using video footage and images taken by remotely operated vehicles (ROVs). Before the 2010 catastrophe spewed approximately 4.2 million barrels (over 176 million gallons) of crude oil into the Gulf of Mexico resulting in America’s worst environmental crisis to date, researchers observed healthy and colorful gorgonian sea fan corals on Pinnacle Trend with few to no bare branches. Today, “Up to half of the corals exhibited injury in the years after the spill, compared to baseline rates of less than ten percent injury in the years before the spill,” reported lead author Dr. Peter J Etnoyer of NOAA.
Healthy sea fan branches are characterized by colorful polyps that surround the branches and strain food from the water column. The video below shows healthy gorgonian octocorals (Swiftia exserta sea fans) on Roughtongue Reef—one of those affected by Deepwater Horizon in 2010—eight years earlier.
In the summer of 2002, Mission Blue founder and National Geographic Society Explorer-in-Residence Dr. Sylvia Earle led the Sustainable Seas Expedition (SSE) to the Gulf of Mexico, where she and other researchers were instrumental in documenting healthy reef ecosystems in this region. Dr. Earle’s surveys during the Sustainable Seas: Eastern and Western Gulf of Mexico 2002 Expeditions helped set baseline conditions for the now struggling reefs. In 2010, Dr. Earle named the Gulf of Mexico deep reefs a Mission Blue Hope Spot—a special area vital to the health of the ocean—to call attention to their importance and fragility.
Dr. Earle’s daughter, Gale Mead, served on the Sustainable Seas Expeditions as a data manager, project historian, video editor, writer, photographer and submersible pilot. During this expedition she became the first person to see and film the abundance of life on Salt Dome Seamount, 200 meters deep and just 16 miles from where the BP oil well gushed out of control eight years later. In the video below created during the Deepwater Horizon disaster, Mead describes the corals and fish she saw during the 2002 expedition and the devastation she expected the oil and chemical dispersants would cause in an interview with OnEarth Magazine.
Although a bit farther away from the well blowout than Salt Dome Seamount, the reefs of Pinnacle Trend were trapped below the surface oil slick for several weeks, with oil and noxious chemical dispersants churning in the waters above. Dr. Etnoyer of NOAA, Dr. Ian MacDonald of Florida State University and their research colleagues collected imagery of healthy and injured gorgonian sea fan corals from before and after the spill on three of the largest mesophotic reefs directly impacted by the oil slick over Pinnacle Trend. Because Dr. Etnoyer and his colleagues had access to ROV footage from Pinnacle Trend reefs dating back to 1989, they could accurately compare levels of injury to corals on each reef and decipher between damage likely caused by fishing gear versus crude oil and dispersants. Their findings reveal that the three largest reefs close to the well blowout had less evidence of fishing gear damage but notable declines in coral health after 2010, and over half showed signs of injury by 2011 compared to less than one tenth of corals before the disaster. Other sites surveyed farther from the wellhead that had much less exposure to the oil slick exhibited no significant change in coral health.
“Recovery of injured corals is unlikely,” Dr. Etnoyer told NOAA’s Office of Response and Restoration. The most recent study continued through the end of 2014 and found that healthy corals observed after the disaster in 2010 remained healthy while injured corals continued to deteriorate, suggesting that injured corals would have otherwise remained healthy. Moreover, Etnoyer and his co-authors expect that their latest findings may underestimate the extent of damaged mesophotic reefs in the region, noting that the reefs they observed represent under three percent of those known to have existed below the oil slick.
“The corals of the Pinnacle Trend require decades to reach maturity,” said co-author Dr. Ian MacDonald. “Recovery will require years and it may not be immediately apparent whether the injured colonies are being replaced with new settlements. Our task is to study the process—to learn as much as we can and to ensure that nothing impedes this vital natural process.” Etnoyer added, “The reefs have some prospects for recovery since many healthy colonies remain.”
Baseline data presented in these studies and collected by Dr. Earle’s Sustainable Seas Expedition support arguments that British Petroleum should pay settlement funds to restore mesophotic reefs in the Gulf. The Deepwater Horizon Natural Resource Damage Assessment Trustees—the committee in charge of determining the environmental harm from the disaster and response and seeking compensation from those responsible in order to restore affected resources—may accept a settlement with BP that would pay up to $8.8 billion. A portion of these funds could be used to enact a comprehensive, integrated, ecosystem restoration plan, drafted here.
Top image: An injured sea fan, Hypnogorgia pendula, on Alabama Alps Reef following the Deepwater Horizon oil disaster. Image courtesy Dr. Ian MacDonald, Florida State University.