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A dead fish coated in heavy oil floats near shore June 4, 2010 near East Grand Terre Island, Louisiana. (Win McNamee/Getty Images)
A dead fish coated in heavy oil floats near shore June 4, 2010 near East Grand Terre Island, Louisiana. (Win McNamee/Getty Images)

How the gushing oil in the Gulf will ripple around the world Add to ...

Damage to fragile coral reefs as far away as Cuba, vanishing red snapper in North Carolina and oxygen-depleted dead zones in the Gulf of Mexico.

Oil-soaked birds may be the iconic image of what happens when an oil spill collides with an ecosystem, but the sheer size and scope of the Deepwater Horizon disaster is causing scientists to nervously explore worst-case scenarios far beyond soiled beaches or dying pelicans.

A small army of scientists is already deploying along the Gulf Coast to study the spill's effects.

"Just about everyone on the planet, one way or another," will feel the impact of this spill, argued Sylvia Earle, the National Geographic Society's explorer in residence and former chief scientist at the U.S. National Oceanic and Atmospheric Administration.

"We now understand there are limits to what we put into, or take out, of this or any other part of the ocean, without unfavorable consequences back to us."

As experts ponder the potential long-term environmental fallout from the disaster, U.S. President Barack Obama is grappling with a more immediate problem - limiting political damage now. Mr. Obama made his second trip in a week Friday to the Gulf region as he struggles to get on top of a crisis that threatens to be a defining event of his presidency.

"This has been a disaster for this region," Mr. Obama said shortly after arriving in New Orleans, "and people are understandably frightened and concerned about what the next few months and the next few years may hold."

The good news about the practical aspects of the spill is marine ecosystems are remarkably resilient. Much of the oil will dissolve, naturally and with the help of special chemical dispersants. The Gulf's warm waters and scorching sun will help the chemicals break down and accelerate evaporation - much faster than after the Exxon Valdez spill in the cooler climes of Alaska.

Consumer advocate Barbara Holzer holds up a model duck coated in chocolate syrup made to look like oil at a protest outside BP's offices in Washington.

Resilient, yes, but not immune. A significant amount of crude will inevitably come in contact with animals, wetlands and coral before that happens. Some oil may be trapped in marshes, wreaking havoc for years.

No one knows with certainty what will happen - six months out, in a year or decades from now. One huge unknown is how long crude will continue gushing out of the ruptured well, which has already dumped 21 million to 46 million gallons into the Gulf.

"There's a lot of fear of death and destruction," acknowledged Stan Senner, director of conservation science for the Ocean Conservancy. Mr. Senner lived through the Exxon Valdez spill, working as both an Alaska and U.S. government scientist.

"We don't have the science to be predictive of the long-term effects. But we're watching it closely," said Mr. Senner, who recently returned from a two-week trip to the Gulf spill.

People should start thinking beyond the coast to look at the oil's impact on the water column, the sea floor and the powerful currents that are already transporting crude far from the spill site, located 80 kilometres off the Louisiana coast, according to Doug Rader, chief oceans scientist at the New York-based Environmental Defense Fund.

"Sea birds covered in oil are only a tiny tip of the oil pollution iceberg," he said from North Carolina.

The oil that doesn't come to shore is already mixing with powerful currents that run through the northern Gulf. These currents act as superhighways that move sought-after eating fish, such as grouper, snapper and tuna, from where they spawn to where they feed - sometimes hundreds of kilometres away. Studies have shown red snappers that spawn in the Gulf may travel as far north as North Carolina.

Moving down through the water column to the sea floor, larger predator fish dive deep to feed on jellyfish, squid, shrimp and other prey. If the oil affects any of these species, it hits the fish that dine on them. Exposed to enough oil, generations of fish could be wiped out, with potentially devastating ripple effects through the food chain, according to Mr. Rader.

"If the Midwest is our bread basket, the Gulf is America's fish basket," Mr. Rader said.

In the Gulf and beyond, there are highly sensitive coral reefs that are vital to fish and protection of coastlines. Now directly in the path of the moving Gulf oil slick are the Dry Tortuga reefs off the Florida Keys, part of a reef and island system that extends to Cuba.

Oil that that doesn't evaporate may sink to the bottom as it travels along the current to Florida and beyond. Studies have shown crude oil, laced with dispersants, can eat away at coral within hours.

Scientists also fret about the consequences of the loss of fragile wetlands in the Mississippi Delta. Marshes and wetlands act as a giant sponge-like filter for the fertilizer-infused waters of the Mississippi that drain into the Gulf from roughly half the continental United States. The marshes are a breeding ground for one of the most lucrative fisheries in the world, including shrimp and oysters. They're also a buffer against the violent storms and hurricanes that routinely lash the coast.

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