A dead fish coated in heavy oil floats near shore June 4, 2010 near East Grand Terre Island, Louisiana.Win McNamee/Getty Images
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.
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.
In heavy concentrations, oil can kill the grasses and vegetation that protect the land from the advancing sea. Louisiana is already losing an estimated 10,000 hectares of wetlands every year. That's the equivalent of a football field every minute. Since the 1930s, roughly 3,700 square kilometres of Louisiana shoreline has been submerged, due in large part to the dredging and channelling of the Mississippi.
Future storms could stir up oil trapped in the marshes, replaying the damage year after year.
"The amount of oil already loose in the Gulf means that significant changes are to be expected in the fundamental ecological engine of the northern Gulf of Mexico," Mr. Rader explained.
"The legacy will be with us for decades, and that's the best case. There is already so much material hitting so many key components in the system because of the scale of the gusher."
Some scientists say predictions about the effects of the spill are pointless because there's so much they don't know yet. Christopher Reddy, associate scientist at Woods Hole Oceanographic Institution in Massachusetts, has been studying oil spills for more than a decade. And none, is quite like the last one, he pointed out.
"Every oil spill is unpredictable," explained Mr. Reddy, who is now in the Gulf on a grant from the U.S. National Science Foundation. "Nature, and oil, don't take directions well."
When he's closer to home, Mr. Reddy loves taking visitors into the Wild Harbor salt marsh near West Falmouth, Mass. Near there, on a foggy night in 1969 an oil barge ran aground, dumping 200,000 gallons of fuel oil. By the early 1970s, the coastline had virtually returned to normal, at least to the naked eye.
Even now, 41 years later, dip a stick into the muck, lift it up, and the unmistakable smell of crude wafts up. A small fraction of the spilled oil remains trapped in the mud, deprived of oxygen, and still affecting crabs and vegetation.
"It can look postcard-perfect, but underneath, chemical warfare may be going on," Mr. Reddy said.
He hastened to add that a similar barge spill near Portland, Maine, in 1996 took barely a year to completely clean up.
"Some spills clean themselves up pretty quickly. Others have effects that last for decades," he said.
Jeffrey Short, a former research chemist at the U.S. National Oceanic and Atmospheric Administration, shares Mr. Reddy's concerns about making too many predictions. He and other scientists acknowledged there are so many unknowns, from wind patterns to the amount of oil in the water.
Mr. Short, who worked for the Alaska and U.S. governments on the Exxon Valdez assessment and cleanup, also knows how difficult and costly it is to get rid of oil once it makes contact with land and animals.
His greatest fear is the amount of oil getting into the marshes and wetlands along the Gulf coast. All it would take is for onshore winds to move the oil that's now drifting on the loop current back toward the marshes to cause significant, long-term damage.
"The process of getting it out can be very slow," he said. "It could create enough of an impact that could take a decade or more to get over."
At nearly 11-million gallons, the Exxon Valdez was the largest U.S. spill until the Deepwater Horizon. The Exxon Valdez, however, doesn't even rank among the top 10 worst spills in the world.
Dire predictions have been made after major disasters, only to be proven unfounded. Many scientists predicted an environmental apocalypse after the largest spill in history - Saddam Hussein's release of 240-million gallons of oil into the Persian Gulf in 1991. In the end, there was little permanent damage. Half the oil evaporated and another quarter washed ashore in Saudi Arabia.
In 1979, there was a spill eerily similar to the Deepwater Horizon, but even larger. An oil well in Mexico's Bay of Campeche collapsed when a pressure build-up sparked an explosion. In the 10 months it took to cap the well, 140-million gallons spilled into the Gulf, creating an 1,800 square kilomentres oil slick.
Mexican officials sprayed the slick with chemical dispersants. Some of the oil made it as far as the barrier islands of Texas. But three decades later, the accident is a distant memory.
Mr. Rader of the Environmental Defense Fund said the best thing that has come of this spill is it gets people thinking about better managing the Gulf for all the countries that depend on its bounty. That means more focus on protecting wetlands and coral reefs, and working to mitigate the dumping of nutrients into waterways.
"The best case would be that this is a bellwether that causes us to build a multilateral environmental management that takes into account changes to the planet that we know are coming," he said.