Deepwater Horizon: After the oil (Nature news feature)

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http://www.nature.com/news/2010/100901/full/467022a.html

Oil has been here. It has blasted this tiny barrier island on the southeastern edge of Louisiana, turning the entire rim of wetland vegetation yellow and the surrounding soil black. The flagging marsh grass stems are tinged dull brown, as if they've been dipped in turpentine. As for the animals living in the water below — well, it is hard to know their story.

Kim de Mutsert, a postdoctoral coastal ecologist from Louisiana State University (LSU) in Baton Rouge, is here on a blistering July day to find out. The juvenile crabs, shrimp and fish she is collecting spawned tens to hundreds of kilometres away on the continental shelf in April and May — just when the Deepwater Horizon well was spilling some 10 million litres of oil a day into the Gulf of Mexico. Their eggs and larvae drifted for weeks offshore, bathed in oily water, before the juveniles at last took refuge in the shallow coastal estuaries, where they will mature. De Mutsert is here to discover what harm they have sustained, and what scars will be left on their offspring and on the generations to come.

By the time the Deepwater Horizon well was finally plugged on 15 July, it had spewed some 750 million litres of crude oil into the Gulf and earned the title of the biggest accidental marine oil spill ever. Much of the oil has already vanished from surface waters, and so far the most visible effects have been oiled seabirds, turtles and salt-marsh fringes. Drawing on lessons from past oil spills, many scientists agree that ecosystems have a remarkable capacity to heal. "This is not the end of the Gulf of Mexico," says George Crozier, a marine biologist and head of the Dauphin Island Sea Lab in Alabama.

But history provides an incomplete reference. Aside from its unprecedented size, the spill was the first to release a massive amount of oil 1.5 kilometres down on the sea floor and the first involving widespread use of oil dispersants below water. On top of that, the coastal areas hit hardest — the Louisiana wetlands — are already under acute stress from subsidence, erosion and the damage caused by Hurricane Katrina in 2005. All this means that the long-term consequences for life in the deep water and coastal ecosystems in the Gulf remain unknown. Researchers worry that toxic components in the oil could wipe out generations of some species, but there is no way to predict the effects. And the oil could linger both in the deep ocean and in sediments for months or years, slowly bleeding more pollutants (see 'The unknown fate of oil'). "It's a huge lab experiment, but there are no controls," says Harriet Perry, a fisheries biologist at the University of Southern Mississippi's Gulf Coast Research Laboratory marine-science centre in Ocean Springs, Mississippi. "That's frightening to scientists who always have a control to measure against."

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