March 27, 2012
Gulf Oil Spill Seriously Impacted Deep-Sea Corals: Study
redOrbit Staff & Wire Reports - Your Universe Online
Scientists reported on Monday that they have found “compelling evidence” that the Deepwater Horizon oil spill in the Gulf of Mexico has seriously impacted deep-sea corals."These biological communities in the deep Gulf of Mexico are separated from human activity at the surface by 4,000 feet of water,” she said,” said Helen White, Assistant Professor of Chemistry at Haverford College and lead author of the study.
“We would not expect deep-water corals to be impacted by a typical oil spill, but the sheer magnitude of the Deepwater Horizon oil spill and its release at depth make it very different from a tanker running aground and spilling its contents.”
“Because of the unprecedented nature of the spill, we have learned that its impacts are more far reaching than those arising from smaller spills that occur on the surface,”
The researchers used a wide variety of underwater vehicles, including the research submarine Alvin, to investigate the corals. They also used comprehensive two-dimensional gas chromatography to precisely determine the source of the petroleum hydrocarbons they found.
The current study grew out of an initial research cruise to the Gulf by Penn State biologist Charles Fisher in October 2010 -- about six months after the Deepwater Horizon spill.
Using the remotely operated vehicle (ROV) Jason II, Fisher and his team examined nine sites at distances greater than 20 km from the Macondo Well, and found deep-water coral communities unharmed.
However, when the ROV explored another area 11 km to the SW of the spill site, they discovered numerous coral communities covered in a brown flocculent material and showing signs of tissue damage.
"We discovered the site during the last dive of the three-week cruise," said Fisher, who also served as lead researcher on the current study.
"As soon as the ROV got close enough to the community for the corals to come into clear view, it was clear to me that something was wrong at this site,” he said.
“I think it was too much white and brown, and not enough color on the corals and brittle stars. Once we were close enough to zoom in on a few colonies, there was no doubt that this was something I had not seen anywhere else in the Gulf: an abundance of stressed corals, showing clear signs of a recent impact. This is exactly what we had been on the lookout for during all dives, but hoping not to see anywhere,” he said.
These coral communities were at a depth of 4300 feet in close proximity to the Macondo well, which had been capped three months before after spilling an estimated 160-million gallons of oil into the Gulf.
Because the timing and unprecedented nature of this observation suggested that the damage observed visually resulted from the Deepwater Horizon oil spill, the scientists quickly organized a second research cruise, which began just one month later.
For the second research cruise, also led by Fisher, the researchers used the autonomous underwater vehicle Sentry to map and photograph the ocean floor, and the deep-submergence, 3-passenger, robotic-armed vehicle Alvin to get a better look at the distressed corals.
During six dives in Alvin, the researchers collected sediments and samples of the corals, and filtered the brown material off of the corals for analysis.
To identify the oil found in the coral communities, White and colleagues used an advanced technique known as comprehensive two-dimensional gas chromatography, which separates oil compounds by molecular weight, allowing scientists to "fingerprint" oil and determine its source.
This exacting petroleum analysis, combined with the analysis of 69 images from 43 individual corals at the site, yielded strong evidence that the coral communities were indeed impacted by oil from the Macondo well spill.
Fisher said the findings confirm a significant impact from the spill on the animal communities in the deep sea more than 7 miles from the Macondo well.
"Our ongoing work in the Gulf will allow us to better understand the long-term effects of the spill on the deep sea, and to constrain the footprint of the impact zone for deep-water corals around the Macondo well,” he said.
The study was published Monday in the journal Proceedings of the National Academy of Sciences.