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Dissolving into patches, sheens, tarballs and microdrops, the oil slick spreading from the damaged Deepwater Horizon well is creating a unique mosaic of potential hazards that has marine biologists, health experts and wildlife activists juggling hopes and fears.
It is a spill like no other, taking place a mile or so deep under water, in layers of more shallow water and also on the surface. The oil and the dispersant chemicals used to dissolve it are potent variables in the biochemical equation of life across the Gulf of Mexico, said several marine biologists, oceanographers and wildlife experts, who are scrambling to understand how large or long-lasting the region's problems may become.
"This is a three-dimensional spill," said Columbia University oceanographer Ajit Subramaniam. "The physics, the chemistry and the biology action are very different when you have oil released from below."
The damaged well's location, in an area of extensive marine diversity, has heightened scientists' concern. Around the spill zone, marine researchers have cataloged 1,728 species of plants and animals, such as crabs, shrimp, marine mammals and sea turtles. Of those, 135 are unique to the area and 74 species are endangered, according to a comprehensive marine survey.
"We've thrown a monkey wrench into that ecosystem," said marine oil-spill expert Chris Reddy at the Woods Hole Oceanographic Institution in Massachusetts. "There are uncertainties about the long- and short-term impacts."
Under the best-case scenario, the effects of so much oil may taint Gulf fisheries for only a season. But even brief exposures to the oil could further weaken species already listed as threatened or endangered.
"Depending on where the oil spill moves and when, it has the potential to harm five different species of sea turtles, all of which are listed as threatened or endangered," said marine scientist Elizabeth Griffin Wilson at Oceana, an environmental group opposed to offshore drilling.
Ideally, the scientists said, eddy currents may continue to sequester much of the oil offshore, where naturally occurring bacteria can safely break down the toxic petroleum compounds. Life in the Gulf of Mexico evolved in a world of oil: In addition to the 4,000 commercial oil platforms operating in the Gulf, there are 1,500 or so natural seafloor seeps that leak about 15 million gallons of oil every year.
Under the worst-case scenario, however, the oil spill could fundamentally alter the marine chemistry of the Gulf, making it less hospitable to the marine life that makes the region a valuable commercial fishery.
"You could end up changing the ecosystem completely," said Columbia University marine biologist Andrew Juhl, who studies marine pollution. "The things that tend to live in polluted areas are not the sorts of things we like."
The approaching hurricane season is compounding the uncertainty because storms could curtail the effects of the oil spill or worsen them.
"The big jokers in the deck now are hurricanes," said marine ecologist Thomas Shirley at Texas A&M University. Forecasters have predicted as many as 14 major hurricanes in the coming season. Depending on their strength, duration and direction, they may dramatically alter the dynamics of the oil spill in the Gulf.
In the best-case scenario, hurricane winds could whip up waves that would more rapidly dilute and disrupt surface oil slicks so that they could be digested by natural bacteria. In the worst case, however, a hurricane-driven storm surge could drive oily saltwater deep into freshwater marshlands, smothering plants and killing wildlife far from the wellhead.
"If that water is carrying oil as well as salinity, there is a double whammy," said Dr. Shirley.
Until it was partly contained, the well gushed as many as 50,000 barrels a day into the Gulf, according to the newest calculations by government and university experts. All the while, low concentrations of that oil spread on subsea currents in billows of microdroplets as many as 45 miles from the well site.
As of Thursday, crews had sprayed 798,000 gallons of chemicals to disperse the oil at the surface and injected another 346,000 gallons under water to break it up near the seafloor. In 142 controlled fires, crews also burned an estimated 3.62 million gallons of oil on open water. About one-third of the Gulf remains closed to fishing.
"We are not really dealing with a monolithic spill," said national incident commander Admiral Thad Allen earlier this week. "We're dealing with about a 200-mile radius around the well site with thousands—maybe hundreds of thousands—of smaller patches of oil."