Four years after the largest marine oil spill in history, biologists continue to discover its victims on the ocean floor.
Transocean Ltd. and BP’s drilling rig, the Deepwater Horizon, exploded in the Gulf of Mexico on April 20, 2010, killing 11 crewmen and igniting a fire that could be seen from the Louisiana shore over 40 miles away. Two days later, the rig sank 5,000 feet to the ocean floor, gushing oil out into the water at a rate of roughly 60,000 barrels a day for 87 days. By the time the well was capped that September, it had released nearly 5 million barrels (210 million gallons) of oil and gas into the ocean. Covering an area of nearly 30,000 square miles, the oil slick on the water’s surface was almost the size of South Carolina.
Cleanup efforts were primarily surface-level. The slick was dissipated with the help of 1.8 million gallons of Corexit dispersants, which change the chemical and physical properties of oil but do not reduce the total amount of oil entering the environment. After these dispersants were pumped into the water and applied aerially to the slick, booms contained the remaining oil so it could be siphoned off or burned.
Far beneath the surface, the effects of the spill and the cleanup strategies have been difficult to gauge. “Things happen slowly in the deep sea,” says Charles Fisher, the Pennsylvania State University biology professor who led a study published Monday in the online Early Edition of Proceedings of the National Academy of Sciences. The paper reports the discovery of five previously unknown coral communities near the wellhead, two of which show signs of damage resulting from the spill.
Prior to the study published Monday, only one known coral site was visibly affected by the spill. Discovered eight miles southwest of the wellhead, it was one of 14 coral communities that Fisher’s team visited in the fall of 2010 and was the only one that “clearly suffered a recent severe adverse impact,” according to the report. Using oil forensics, the team determined that hydrocarbons found on the corals at that site originated from the Deepwater Horizon.
Now they know it was not an isolated incident. Of the five newly discovered coral communities, two show the same signs of degradation that the team’s 2010 discovery reflected. And since one of the new sites is nearly 14 miles southeast of the wellhead—almost twice as far and in 50 percent deeper water than the first discovery—these findings considerably expand the spill’s known area of impact.
“It is important to remember that this isn’t just about corals,” Fisher tells Newsweek. For one thing, these communities are among the most biologically diverse and productive on the planet, and it could spell disaster if their destruction reduces biodiversity and ocean productivity. What’s more, since they are one of the oldest living animals on Earth, corals serve as excellent indicators of man’s impact on marine ecosystems. Natural death of deep-sea coral is a rare event, with some species living thousands of years. Furthermore, when a colony dies, its skeleton remains attached to the seafloor for years, slowly losing branches as it continues to provide a record of its existence and death.
“If fish or crabs or shrimp were swimming around in those areas [in 2010], we wouldn’t have known,” Fisher says. “But these corals stay there.” Looking at them can give us an idea of what ocean conditions have been like throughout time.
What the three coral communities affected by the Deepwater Horizon spill all have in common is a characteristically patchy dispersion of dead coral skeleton covered with hydrozoans (a.k.a. “immortal jellyfish”), which grow on any substrate, dead or alive, and resemble either mutant jellyfish or soft coral, depending on their stage in life. These hydrozoans and the dead spots they cover are randomly scattered not only across the site but also on individual coral colonies.
“This pattern suggests that the impacting agent was not evenly dispersed in the bottom water, but rather present as microdroplets or particles,” according to the report. “Whether this represents small droplets of oil/dispersant or oil-containing marine snow is not known.”
Marine snow is a natural process, in which organic materials rain down from the upper layers of the water column to the ocean depths below. Fisher says marine snow could have become toxic four years ago, as globs of oil or dispersant or byproducts from the oil fires began to sink. But toxic marine snow is just one theory. The mechanism that carried the hydrocarbons so far and so deep to speckle the coral where they were found is unknown, but Fisher’s team is certain that their origin was either the Deepwater Horizon spill or the cleanup.
And they’re surprised because “the models all said the plumes didn’t go that deep,” Fisher says. The National Oceanic and Atmospheric Administration models, to which he is referring, suggested that the deep-water plume of hydrocarbons from the spill moved predominantly to the southwest, whereas these new corals were found to the southeast. Furthermore, the old models capped their depth predictions at 1,300 meters (0.8 mile), and the one found almost 14 miles from the wellhead was 1,900 meters (1.2 miles) deep.
Two of the other five newly discovered coral communities were also damaged, but not by the events of 2010. They were fouled by commercial fishing lines, the report found, adding to the “large cumulative effect” of harmful human activities on the corals in the deep Gulf of Mexico.
“Although far removed from surface and coastal waters, and from the consciousness of most people, deep-sea environments play numerous roles,” the authors of the study write. “Many species of fishes and sharks use deep corals as spawning grounds or sites for deposition of eggs. Healthy deep-sea sediments are remarkably high in biodiversity and important in global carbon and nitrogen cycling, decomposition processes, and energy flow to higher trophic-level consumers. Perhaps most importantly, the full spectrum of ecosystem services derived from deep-sea biota and habitats is largely unknown.”
In other words, the full damage of the Deepwater Horizon spill may still be unknown.