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A sweeping survey of coral communities surrounding the site of the Deepwater Horizon oil spill in the Gulf of Mexico shows that the catastrophe had a wider effect than scientists thought four years ago.
"This study very clearly shows that multiple coral communities, up to 22 kilometers from the spill site and at depths over 1,800 meters, were impacted by the spill," said Penn State biologist Charles Fisher, lead author of the report being published online this week in the Proceedings of the National Academy of Sciences.
Six months after the 2010 spill, an initial survey showed that severe damage was done to coral as far away as 13 kilometers (8 miles) away from the deep-sea oil leak. But as the oil dissipated, it became more difficult to gauge the impact. Fisher and his colleagues used the damaged coral community as a model to look for the telltale signs of the oil's effect — for instance, the presence of feathery growths known as hydroids.
The scientists scanned an area within a 25-mile (40-kilometer) radius of the leak, using sonar data, towed camera systems and an autonomous Sentry underwater vehicle. Five previously unknown coral communities were identified, and an ultra-heavy-duty Schilling remotely operated vehicle was dispatched to take high-resolution pictures.
"When we compared these images with our example of known oil damage, all the signs were present providing clear evidence in two of the newly discovered coral communities of the impact of the Deepwater Horizon oil spill," Fisher said in a news release.
The survey also turned up two coral sites that were entangled with fishing line — a reminder that oil spills aren't the only human-caused threat to marine species.
In addition to Fisher, the authors of "Footprint of Deepwater Horizon Blowout Impact to Deep-Water Coral Communities" include Pen-Yuan Hsing, Carl Kaiser, Dana Yoerger, Harry Roberts, William Shedd, Erik Cordes, Timothy Shank, Samantha Berlet, Miles Saunders, Elizabeth Larcom and James Brooks. An online slideshow documents the coral damage.