Madrid. The deep-sea corals in the Gulf of Mexico are still grappling with the devastating effects of the 2010 Deepwater Horizon oil spill. A decade after the oil spill, the corals are showing limited signs of recovery, with some continuing to decline, according to a presentation at the New Orleans Ocean Science Meeting.
The research involved a comparison of images of more than 300 of the deep-sea corals over a span of 13 years, which is the longest time series of deep-sea corals to date. The Deepwater Horizon oil spill resulted in 500,000 tons of oil spilling directly from the wellhead into the gulf at a depth of 1,520 meters over 87 days. This created an oil slick the size of Virginia, covering hundreds of miles of coastline and extending hundreds of meters into the ocean.
Fanny Girard, a marine biologist and conservationist at the University of Hawaii at Manoa, who led the research, said, We always knew that deep-sea organisms take a long time to recover, but this study proves it. Although in some cases the health of the corals appeared to have improved, it was impressive to see that the most affected individuals are still struggling, and even deteriorating, a decade later.
The research findings can provide valuable insights to guide restoration efforts in the deep sea following oil spills.
After the Deepwater Horizon well was plugged, an interdisciplinary team of experts surveyed the ocean floor 6 to 22 kilometers from the wellhead to record the damage. Approximately 10 kilometers away and 1,370 meters deep, they discovered a dense forest of tree-shaped Paramuricea corals that appeared ill. These corals were covered in a brown material,
Girard observed.
Contaminated particles
Tests revealed that the sludge contained traces of a combination of petroleum and chemical dispersants. A few months later, the researchers discovered two more coral sites at depths of 1,580 meters and 1,875 meters that had suffered similar damage.
Deep-sea corals are suspension feeders and may have ingested contaminated particles, leading to the observed health impacts. Direct exposure to the toxic chemicals in the oil mixture may have also damaged the coral tissue. However, exactly how the oil and dispersant affected these vulnerable organisms is still not fully understood by scientists.
Each year between 2010 and 2017, scientists visited the three affected sites to assess the damage, measure growth rates, and observe any signs of coral recovery. This was part of a larger initiative aimed at enhancing our understanding of the impacts on ecosystems and improving our ability to respond to future oil spills. Using a remotely operated vehicle, they took high-resolution photographs of the corals at the three affected sites and two distant reference sites, monitoring more than 300 corals in total.
In 2022 and 2023, researchers revisited these sites as part of the Habitat Assessment and Assessment project, which was funded through the Natural Resources Damage Assessment agreement. The photographs allowed the team to measure changes in the corals’ health over time, including noting any breaks in the delicate branches of the corals caused by exposure to oil pollution.
The researchers found that even in 2022, the corals that were affected by the oil spill were still exhibiting signs of stress and damage. The brown coating that was initially observed had long since disappeared, but upon closer inspection, the corals appeared weak and prone to breaking. The areas where the corals’ branches had fallen off were oozing mucus, and some specimens that had their skeletons exposed had been colonized by parasitic species.
Girard emphasized the importance of taking protective measures to prevent damage to these vulnerable organisms: It’s really important to prevent damage in the first place, and the way to do that is through protective measures.