By Barbara Kennedy, Penn State
On a research ship in the Gulf of Mexico on Tuesday, Nov. 2, seven miles south-west of the site of the Deep Water Horizon oil-spill, a team of scientists discovered a community of corals that includes many recently dead colonies and others that clearly are dying. “We discovered a community of coral that has been impacted fairly recently by something very toxic,” said the chief scientist on the cruise, Charles Fisher, who is a professor of biology at Penn State and a member of the research team that selected the site for study.
Fisher said the research team encountered a colony of the hard coral species Madrepora that appeared to be unhealthy on Nov. 2, at a depth of 1,400 meters.
“Although some branches of the coral colony appeared normal, other branches clearly were covered in a brown material, apparently sloughing tissue, and were producing abundant mucous,” Fisher said. The scientists sampled pieces of this hard coral and of its immediate environment then, about 400 meters away, they found a seriously stricken community of soft corals.
“Within minutes of our arrival at this site, it was evident to the biologists on board that this site was unlike any others that we have seen over the course of hundreds of hours of studying the deep corals in the Gulf of Mexico over the last decade with remotely-operated-vehicles (ROVs) and submersibles,” Fisher said. “We found that extensive portions of most of the coral colonies were either recently dead or were dying. Most of the soft coral sea fans had extensive areas that were bare of tissue, covered with brown material, and/or had tissue falling off the skeleton. Many of the colonies appeared recently dead, with no living coral tissue, still covered with decaying material, and also with a notable lack of colonization by other marine life, as would be expected on coral skeletons that had been dead for long periods of time,” Fisher said.
The scientists also found that many of the brittle stars that are the typical symbiotic partners of these types of corals also appeared to be very unhealthy.
“Many of the dead and dying coral colonies had discolored and immobile brittle stars — a kind of starfish — still attached,” Fisher said.
The team took a variety of samples that will be analyzed for the presence of hydrocarbons and for molecular evidence of genetic damage and physiological stress that could give direct evidence of exposure to oil or dispersants from the Deep Water Horizon disaster. However, Fisher said it is possible that lab results might not be able to provide any new information.
“For example, a plume of toxic dispersant or oil blowing through this community could have caused damage that resulted in the slow death of the corals without leaving any trace on the sea floor near the corals,” Fisher said. “No one yet knows if the signature of whatever toxin killed these corals can be found in their skeletons after the tissue sloughs off. No one even knows if dispersant accumulates in the tissues that it kills.”
However, “The compelling evidence that we collected constitutes a smoking gun,” Fisher said. “The circumstantial evidence is extremely strong and compelling because we have never seen anything like this — and we have seen a lot; the visual data for recent and ongoing death are crystal clear and consistent over at least 30 colonies; the site is close to the Deep Water Horizon; the research site is at the right depth and direction to have been impacted by a deep-water plume, based on NOAA models and empirical data; and the impact was detected only a few months after the spill was contained.”
“The proximity of the site to the disaster, the depth of the site, the clear evidence of recent impact, and the uniqueness of the observations all suggest that the impact we have found is linked to the exposure of this community to either oil, dispersant, extremely depleted oxygen, or some combination of these or other water-borne effects resulting from the spill,” Fisher said.
The research is funded jointly by NOAA’s Office of Ocean Exploration and Research and the Bureau of Ocean Energy Management, Regulation, and Enforcement through TDI Brooks International. The research team, which includes scientists from Penn State University, Temple University, Woods Hole Oceanographic Institution, the U.S. Geological Survey, Louisiana State University, Florida State University, the Past Foundation, and C&C Technologies, has been using the NOAA Ship Ronald H. Brown and the National Deep Submergence Facility ROV Jason II in its studies of the coral ecosystems of the deep Gulf of Mexico. The scientists have carefully mapped and imaged the entire coral community with high-definition video and still cameras so it can be revisited during a scheduled cruise with the submersible Alvin in December, and so that it also can be monitored into the future.
