|Do Oil and Corals Mix?
WHOI scientists explore impacts of Deepwater Horizon
Scientists from Woods Hole Oceanographic Institution (WHOI) helped find strong evidence that the Deepwater Horizon oil spill in 2010 had impacts on deep-sea coral communities in the Gulf of Mexico.
The study, published March 2012 in Proceedings of the National Academy of Sciences, used all of the deep-sea robotic vehicles of the WHOI-operated National Deep Submergence Facility—the three-person submersible Alvin, the remotely operated vehicle Jason, and the autonomous underwater vehicle Sentry—to investigate corals near the ruptured Macondo well.
“These corals exhibited varying levels of stress, including bare skeletons, tissue loss, and excess mucus production—all associated with a covering of brown flocculent material,” said WHOI biologist Tim Shank.
The study’s lead author, Helen White, a geochemist at Haverford College, worked with WHOI marine chemist Christopher Reddy and WHOI research specialist Robert Nelson to identify oil found in the coral communities. They documented evidence that its source was the Macondo well, using an advanced technique called comprehensive two-dimensional gas chromatography, which was pioneered at WHOI by Reddy and Nelson. Pen-Yuan Hsing, a graduate student at Penn State University (PSU), documented further evidence by analyzing 69 images of 43 individual corals taken with cameras on undersea vehicles.
The study grew out of a research cruise to the Gulf led by PSU biologist Chuck Fisher in late October 2010, six months after the Deepwater Horizon oil spill. This expedition was part of an ongoing study of deep-sea life in the Gulf funded by the Bureau of Ocean Energy Management and the National Oceanic and Atmospheric Administration. Using Jason, the team discovered numerous distressed and flocculate-covered coral communities 6.8 miles from the Macondo well.
Despite the corals' proximity to the well, when they were first observed, the visible damage could not be directly linked to the Deepwater Horizon spill. The research team, again headed by Fisher and augmented by White, returned a month later, funded by the National Science Foundation’s RAPID Collaborative Research grant program.
“It is easy to see the impact of oil on surface waters, coastlines, and marine life, but this was the first time we were diving to the seafloor to examine the effects on deep-sea ecosystems,” White said. On its return trip, the team employed Sentry to map and photograph the ocean floor and Alvin to get a better look at the distressed corals.
“We don’t know the long-term impacts on these corals,” Shank said. “Beyond that, the corals serve as hosts to other animals—crabs, shrimp, and brittle stars—that may be affected by the loss of their habitat. We hope our continued monitoring of this site will give us insight into whether they will recover.”
—Eils Lotozo and Stephanie Murphy
Erik Cordes (Temple University), Chris German and Rich Camilli (WHOI), Walter Cho (now with Gordon College), and other scientists from Penn State, Temple, and the U.S. Geological Survey contributed to this research.
Gorgonian corals observed at two times a month apart, at a site 6.8 miles (11 km) from the Macondo well, site of the Deepwater Horizon oil spill. In both November (left) and December, 2011, many branches of one large coral were coated with dark, flocculent material. Some branches had lost their living tissue, which appears bumpy and yellow, and had been reduced to bare skeleton. The tips of some branches (arrows) were alive at both times. Branches of another coral (circle) were coated with flocculent material in November but appeared to have shed much of that and largely recovered by December. The corals were photographed by scientists in the submersible Alvin. (Photo courtesy of Chuck Fisher, Penn State University; copyright Woods Hole Oceanographic Institution)
» Tim Shank's lab
Ocean Topic on corals
» Ocean Explorers Probe Gulf of Mexico
Oceanus slideshow of creatures Tim Shank observed in the depths of the Gulf
» Assessing the Impacts of Deepwater Horizon
Video from WHOI's Science in a Time of Crisis website
» National Deep Submergence Facility
Read more about Alvin, Jason, and Sentry
» Every Chromatogram Tells a Story
Oceanus story about using comprehensive two-dimensional gas chromatography to pinpoint the source of spilled oil
Follow the Carbon
WHOI marine chemist David Griffith and his colleagues conducted their fieldwork in 2008 aboard the Canadian Coast Guard icebreaker Louis S. St. Laurent. At two spots in the Canada Basin, an area of the Arctic Ocean northwest of the Canadian coast, they gathered water samples from 24 depths ranging from the surface to the ocean floor 3800 meters (roughly 12,500 feet) below. (Photo courtesy of David Griffith)
The research team led by David Griffith also sampled ice and snow from an ice floe in the Canada Basin. After returning home, they used a mass spectrometer to measured amounts of different carbon isotopes in each specimen to determine where particular pools of carbon came from, how old they are, and how the carbon may have been used and chemically transformed in the ocean. In addition to understanding the basic carbon cycle in the Arctic Ocean, the scientists hope the results of this baseline study will help them evaluate how Arctic Ocean carbon levels and global climate interact. (Photo courtesy of David Griffith)
WHOI scientists provide baseline measurements of carbon in the Arctic Ocean
“Carbon is the currency of life,” said David Griffith, a marine chemist at Woods Hole Oceanographic Institution (WHOI). “Where carbon is coming from, which organisms are using it, how they're giving off carbon themselves—these things say a lot about how an ocean ecosystem works.”
Scientists have had a hard time understanding how the Arctic Ocean’s ecosystem works, stymied by the region’s ice cover and remoteness, said Griffith, an MIT/WHOI Joint Program graduate student. Now he and colleagues have published the first baseline measurements of carbon levels from the sea surface to the seafloor in the polar ocean. The new data, published May 2012 in the journal Biogeosciences, provide an important reference point to help researchers better understand how carbon cycles through the Arctic ecosystem and how the ecosystem will respond to rising global temperatures.
Aboard the Canadian Coast Guard icebreaker Louis S. St. Laurent in 2008, Griffith and colleagues gathered organic carbon particles and carbon dissolved in seawater from 24 depths, ranging from the surface to the seafloor roughly 12,500 feet (3,800 meters) below, in the Canada Basin northwest of the Canadian coast. Collecting samples at those intervals was necessary, Griffith said, because the Arctic Ocean is separated into distinct layers of water, each with its own unique carbon characteristics.
Ann McNichol, a WHOI senior researcher, analyzed the samples at WHOI’s National Ocean Sciences Accelerator Mass Spectrometer Facility. The instrument measured amounts of different carbon isotopes in each specimen, which helps determine where particular pools of carbon came from, how old they are, and how the carbon may have been used and chemically transformed in the ocean.
Measuring the different amounts of carbon in each layer and determining its source are essential steps in understanding how carbon flows through the marine ecosystem, Griffith said. “It’s kind of like understanding how freight and people move in a city. If you don’t know what’s coming in and out, it’s really hard to understand how the city works.”
As the Arctic region gradually warms, more carbon-rich runoff from melting permafrost and eroded soils could end up in the ocean. Bacteria might use the carbon as food, creating carbon dioxide (CO2) as a byproduct and adding more of this greenhouse gas to the atmosphere. Alternatively, the carbon might spur the growth of phytoplankton that use dissolved CO2 and eventually transfer excess carbon to the seafloor, effectively removing it from the environment.
“Those are just a few aspects of what might happen,” Griffith said. “But for every one that we think about, there could be ten others that drive the system in a different direction. Now we have a very important baseline of data to help evaluate changes that will happen in the future. Without that, you‘re unfortunately just guessing at how things change over time.”
This research was funded by the WHOI Arctic Research Initiative, Fisheries and Oceans Canada, the Canadian International Polar Year Office, and the U.S. National Science Foundation. Also collaborating on the study were scientists from the Institute of Ocean Sciences, Fisheries and Oceans Canada, the University of British Columbia, and the Swiss Federal Institute of Technology.
» David Griffith
» Follow the Carbon Trail
Oceanus story about how the links between carbon in the ocean and climate
» Ann McNichol
Posted: September 6, 2012