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Oil that drifts ashore will impact on important breeding grounds for seabirds and many other species, according wildlife experts. Oyster and lobster fisheries could also be badly hit.
"It seems to me yet another man-made environmental tragedy on our hands," said Martin Spray, chief executive of the UK Wildfowl and Wetlands Trust. "The coast of Louisiana has about 40% of the US coastal wetlands so it's a seriously important area. These are incredibly important for their fisheries as well, so there are human livelihoods involved as well."
"The terrible loss of 11 workers may be just the beginning of this tragedy as the oil slick spreads toward sensitive coastal areas vital to birds and marine lifeNational Audubon Society and to all the communities that depend on them," said Melanie Driscoll, a conservation director based in Louisiana for the US (NAS). "For birds, the timing could not be worse - they are breeding, nesting and especially vulnerable in many of the places where the oil could come ashore."
Efforts to stop the oil before it reached shore may not be enough, she said. "We have to hope for the best, but prepare for the worst, including a true catastrophe for birds."
Chris Mann of the Pew Environment Group said: "The Exxon Valdez oil spill provided a mass of scientific data on how oil affects marine life, ecosystems, coastal communities, fisheries and subsistence economies – the effects extend far beyond the inevitable photographs of seabirds, marine mammals and fish covered in oil."
Important bird habitats at risk in the Gulf of Mexico include Chandeleur Islands, Gulf Islands National Seashore in Louisiana and Mississippi and the Active Delta in Louisiana.
The brown pelican, the state bird of Louisiana, nests on islands in the Gulf of Mexico and its breeding season has already started this year. The NAS said many pairs are already incubating eggs. Other species at risk include terns and gulls that nest on the beach, including the Caspian tern, royal tern, laughing gull and the black skimmer. These birds roost on the beaches and also plunge into the water to feed on fish and other marine life. They are therefore at risk from oil on the surface of the water or if it washes ashore.
Similarly, the American oystercatcher, Wilson's plover and snowy plover feed on invertebrates on the beach and could find their sources of food at risk if oil ends up on their sands.
Ocean-dwelling birds such as the magnificent frigatebird could also be affected by oil on the surface of the water that could damage their feathers.
Migratory birds such as plovers and sandpipers are currently on their way from wintering grounds in South America to their breeding grounds near the Arctic. They usually rest and refuel in the Gulf of Mexico on their long journey across the world.
If the oil flows east, it will encounter the seagrass beds that form a key habitat for manatees, among other species.
Carl-Gustaf Lundin, head of the marine programme at the International Union for the Conservation of Nature (IUCN) told the BBC: "If you've got seagrass beds badly contaminated, clearly the manatees could be seriously affected." Less than 2,500 adult manatees remain in the area and are already at risk from climate change and disturbance by boat traffic.
Mann said that the effects of the Exxon Valdez oil spill in Alaska in 1989 can still be found along the beaches in Prince William Sound more than 20 years after the accident. "And research has shown that polyaromatic hydrocarbons - components of crude oil that are highly resistant to weathering - are also highly toxic to marine life."
The accident could also been seen as a warning for those wanting to drill for oil in the Arctic circle, around Alaska. "With decades of experience in drilling in the gulf, and response equipment nearby, the gulf is one of the 'safest' places to drill," said Mann. "If Deepwater Horizon can happen there, it can certainly happen in the Arctic Ocean, where bitter cold, ice, and extreme wind and wave conditions are everyday facts of life and response equipment would be days or even weeks away."