Oil Invades Coral Communities of the Deep
On the deep seafloor of the Gulf of Mexico, ecosystems made up of fish, corals, sea stars, anemones and other invertebrates flourish. Since the sun’s rays don’t reach the deep sea, coral communities rely on nutrients making their way to them from surface waters, dropping down in the form of marine snow.
After the Deepwater Horizon spill dumped 3.19 million barrels of oil into the Gulf of Mexico, the nearby deep-sea environment changed. Oil, gas and dispersant spilled out from the site of the leak, some 5,000 feet below the sea surface. Cloud-like plumes of oil and dissolved gas formed at a variety of depths, and a mixture of oil, dispersant, microbes, and mucus (sometimes called “sea snot”) clumped together, raining down on the seafloor from above.
Not knowing is the nature of working in the deep. Because these ecosystems are so difficult to reach, not a great deal is known about the life histories of deep-sea organisms and how they interact with one another, let alone how they may be affected by a large influx of oil and dispersant. How do you study the impacts of an underwater disaster when you don’t know much about the ecosystem you are studying to begin with?
This is the challenge facing a group of chemists, biologists and physical oceanographers who are studying the impacts of the Deepwater Horizon oil spill on deep-sea communities. The ECOGIG (Ecological Impacts of Oil and Gas Inputs to the Gulf) team, made up of researchers from 14 different institutions and funded by the Gulf of Mexico Research Initiative (GoMRI), is meeting the task head-on with long-term monitoring of sites throughout the Gulf and a multitude of ongoing lab experiments. Dr. Charles (Chuck) Fisher from Penn State University is an ECOGIG researcher who focuses on deep-sea corals, asking questions about how the oil and dispersant associated with Deepwater Horizon impacted coral species that live in the cold and dark of the deep.
Follow some of the expeditions that ECOGIG has made to coral sites in the Gulf of Mexico in our slideshow. See what they are looking for and what they have found.
The Ocean Portal receives support from the Gulf of Mexico Research Initiative (GoMRI) to develop and share stories about GoMRI and oil spill science.
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. For more information, visit http://gulfresearchinitiative.org/.
Where's the Oil Going?
After the spill, researchers returned to known deep-sea coral sites in the region and found no obvious oiling of the corals there. But what about the sites that they hadn’t yet visited?
Scanning For Hard BottomScientists needed to find the undiscovered deep-sea corals in the area, and fast. Corals thrive on hard-bottomed areas in the deep-sea. So rather than go on a wild goose chase, the researchers deployed the autonomous underwater vehicle (AUV) Sentry (seen here being prepared for deployment) to scan the seafloor for telltale signs of hard bottom. In this region of the deep sea a hard bottom can form as a byproduct of bacteria breaking down chemicals seeping up from below. Finding these areas narrowed the search so that they had a better chance of seeing coral at the sites they explored.
Cameron McIntyre, Woods Hole Oceanographic Institution
The researchers discovered a new coral community around eight miles (13 km) away from the spill's source in late 2010. There, more than half of the corals were covered in a brown material called “floc”. Scientists sampled the floc and confirmed that it contained oil from the spill. The corals that were partially covered in floc showed tissue loss and other signs of stress. Corals entirely covered in the substance were dead or dying.
In this image you can see the dark brown floc covering most of the coral, in addition to a lighter colored brittle star clinging to the coral in the middle.
Chuck Fisher, Penn State University
With the help of a camera left behind and return trips to the site, scientists have been able to track the long-term impacts of the floc. At first, corals covered with less floc (roughly 20 percent of their bodies or less) seemed to recover in the years following the spill. But two years after the spill, they were colonized by hydroids and their branches began to break off.
Is There More Out There?
Even some deep-sea corals far away from the spill site were affected. One affected site was 13.7 miles (22 km) away from the Macondo wellhead—the farthest observed—and extremely deep, more than 6,000 feet (1,875 meters) below the surface. This is deeper than any of the reported oil plumes that resulted from the spill. How did oil get down there? Dr. Fisher suspects that those impacts were caused by toxic marine snow falling from above.
Courtesy Charles Fisher
Community LossDeep sea corals are very slow growing and long lived; some of the corals tested in the spill region were over 500 years old. This means that the loss of adult corals can be devastating to the community—and a broken branch could mean losing hundreds of years of growth. If they die, their skeletons remain, leaving an important record of a community that also included species like anemones, brittle stars and clams.
Research cruises, AUVs and ROVs allow scientists to see what is happening to a variety of coral sites in the Gulf. But video and images can only show what is visible to the naked eye. What about the damage that is happening beyond our vision?
ECOGIG researchers want to learn more about how the oil and dispersant may have caused genetic mutations and influenced the reproductive abilities of the coral. To do this, samples of the damaged coral are collected and compared to healthy corals. Pieces of healthy coral are also brought back for observation while exposed to oil and dispersant in the lab.
When will we truly know the impact that the Deepwater Horizon oil spill had on corals, such as this purple octocoral? “It could take years,” says Chuck Fisher. “I had thought that when I first started this work that after a year or so I’d be able to answer that question.” But almost five years later there are still new developments being observed. For these centuries-old animals, five years is just a blink of the eye.