Gulf corals still suffering more than a decade after Deepwater Horizon oil spill, scientists report

The spill coated hundreds of miles of coastline in oil, and covered an ocean surface the size of Virginia. Over the course of 87 days, 134 million gallons of oil flowed directly from the well to a depth of 1,520 meters (about 5,000 feet) into the Gulf. Although this spread was most visible at the surface, the adverse environmental effects extended hundreds of meters into the ocean.

In a presentation on Tuesday, February 20, scientists will show that deep-water corals remain intact long after they have been exposed. Over the past 13 years, these coral communities have seen limited recovery — some are even in steady decline.

“We’ve always known that organisms in the deep sea take a long time to recover, but this study really shows that,” said Fanny Girard, who led the work, a marine biologist at the University of Hawaii. A biologist and conservationist said. “Although coral health has improved in some cases, it was surprising to see that the most affected individuals are still struggling, and even deteriorating, a decade later.”

These findings may help guide deepwater recovery efforts after oil spills.

Fragile and damaged

A few months after Deep water horizon After the well was capped, an interdisciplinary team of researchers surveyed the sea floor 6 to 22 km (3.7 to 13.7 mi) from the well to record the damage. About 7 miles away and at a depth of 1,370 meters (4,495 ft) they found a dense forest of trees. Paramuricea Coral that looked sick.

“These corals were covered in brown material,” Girard said. “Examination revealed traces of oil and chemical spill compounds in the mud. A few months later, researchers found 1,580 meters and 1,875 meters (4,921 and 6,233 feet, respectively).” Two additional coral sites were found at depth that were similarly destroyed.

Deep-sea corals are suspension feeders and can contain particulate matter, causing health effects, the researchers said. Direct exposure to toxic chemicals in oil and chemical mixtures has also damaged coral tissue. However, to this day, scientists still don’t know exactly how oil and spills affect these vulnerable organisms.

Every year from 2010 to 2017, scientists visited the three sites to monitor damage, measure growth rates and note any coral recovery, as part of a larger initiative aimed at environmental To better understand system impacts and improve our ability to respond to future oil spills. They used a remotely operated vehicle to take high-resolution images of corals at all three affected sites and two remote reference sites, tracking more than 300 corals in total.

Researchers revisited the sites in 2022 and 2023 as part of the Habitat Assessment and Evaluation Project, one of the projects funded by the Natural Resource Loss Assessment settlement. The images allowed the team to measure changes in coral health over time, including noting any breaks along fragile coral branches caused by oil pollution.

Still in pain after so many years

The scientists found that by 2022, affected corals continued to show signs of stress and damage from the oil spill. The brown coating they first observed was long gone, but on closer inspection, the coral was fragile and prone to cracking. Scars where branches fell were oozing mucus, and some corals had exposed skeletons colonized by other parasitic coral species.

“Not only were some of these corals not recovering, some of them appeared to be deteriorating,” Girard said. If the impacts are too great, ecosystems may struggle to recover at all, especially given the onslaught of climate change-related stressors such as ocean acidification, he added. “Preventing harm in the first place is really important, and the way to do that is through preventative measures.”

Girard notes that their work is being used to inform restoration strategies, including attempts to grow corals in the deep sea to propagate corals from transplants, to artificial anchorages for recolonization. Protecting deployment or deep water communities and letting nature heal itself. In the coming years, the team will continue to monitor the corals, looking for signs that they’re getting better — or worse.