Photograph by Eric Gay, AP

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A dead Portuguese man-of-war floats on rust-colored oil off the Louisiana coast on Tuesday.

Photograph by Eric Gay, AP

Gulf Oil Spill a "Dead Zone in the Making"?

As the world watches for oil-covered birds, experts warn that the Gulf of Mexico spill could pose greater risks to life deep in the ocean.

Part of an ongoing series on the environmental impacts of the Gulf oil spill.

Other than a few orange tubes encircling a sandbar southwest of Louisiana's Chandeleur Islands, there's no sign anything's amiss.

Dozens of chattering shorebirds—punctuated by the odd pelican—are relaxing on this shallow strip of land in Breton National Wildlife Refuge, known as one of the most important bird breeding grounds in the world. (See pictures of places that could be America's next national parks.)

After heavy rains, experts from a handful of conservation groups traveled by boat Monday to see if oil from the ongoing Gulf of Mexico spill had yet reached the birds at this remote spot. (See a map of Louisiana's barrier islands.)

So far, nothing.

But a heavy band of oil has been spotted at the refuge's back door—"and time is either a friend or an enemy," Larry Schweiger, president of the National Wildlife Federation, said over the avian cacophony.

Even if oil never washes up in the refuge, the region's birds may be silenced if the crude lingers deep in the Gulf of Mexico, experts say.

That's because 5,000 barrels of oil (210,000 gallons, or 794,937 liters) a day are thought to be bleeding from a damaged wellhead at the nearby site of the Deepwater Horizon rig disaster. All that oil is poisoning the less photogenic creatures—plankton, sand crabs, and fish larvae, among others—at the base of the region's food web, Schweiger noted.

If the oil spill can't be contained, the Gulf of Mexico could have another "dead zone in the making," according to Sylvia Earle, a marine biologist and National Geographic explorer-in-residence. (National Geographic News is owned by the National Geographic Society.)

Often caused by algal blooms, dead zones are swaths of ocean devoid of life, save for hardy bacteria. (Related: "Gulf of Mexico 'Dead Zone' Is Size of New Jersey.")

Oil Spill Making Toxic "Chocolate Mousse"

Oil bubbling up from the Gulf of Mexico wellhead, which sits more than 5,000 feet (about 1,500 meters) below the water's surface, is coming from even deeper inside the Earth.

That means the oil is heavier and thicker than the crude spilled in past, tanker-based disasters, noted Ron Kendall, chair of the Department of Environmental Toxicology at Texas Tech University in Lubbock.

When there's turbulent weather—as the Gulf of Mexico has experienced over the past few days—the dense oil mixes with water to form an emulsion, a sort of gooey, chocolate mousse-like substance, Kendall said.

This concoction presents a greater dilemma than the "physical problems of just sticking to a feather," he said. The emulsion is toxic to birds, baby sea turtles, fish embryos, crabs, and shrimp larvae, not to mention sea grasses and marshlands.

What's more, the catastrophe is hitting the Gulf at its most sensitive time of the year—when sea turtles and commercially important species of fish and shrimp are spawning, he noted. (See pictures of how the Gulf oil spill is affecting wildlife.)

"Impacts to the birds will be the thing that is most visible to the public, but it is not just their deaths that we should be concerned about," said John "Wes" Tunnell, associate director of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University in Corpus Christi.

Infauna, or small organisms such as clams and tubeworms that live in ocean sediments, are vital food sources for shorebirds and other coastal animals.

After the 1979 Ixtoc oil spill in the Gulf of Mexico, the area's infauna were reduced by up to 90 percent, Tunnell said—a potential reason many bird species left the area in the wake of the nine-month-long spill.

However, there may be a bright side: Organisms at the bottom of the food chain reproduce more rapidly than bigger animals, Tunnell pointed out by email. After the Ixtoc spill, infauna returned to pre-spill levels within about a year.

Gulf of Mexico's Deadly Experiment

Some scientists also worry about one of the joint federal-industry response team's methods for controlling the oil: dumping chemical dispersants into the Gulf of Mexico.

These chemicals merely break up the oil into smaller droplets, making it less likely to spread—but more likely to drift down and choke life on the seafloor.

"We're wiping out critical elements of the base of the food chain of the Gulf," Texas Tech's Kendall said. "This is an ecotoxological experiment underway in one of the world’s most productive and fragile ecosystems."

As oil droplets spread through the water column, the crude can be fatal to plankton, the tiny, open-ocean creatures that many larger animals depend on, according to marine biologist Earle.

Rescue workers can clean and treat oiled birds and other relatively large animals that come ashore. But "how do you deal with deoiling plankton?" Earle said.

In addition to feeding marine species, plankton suck up carbon dioxide, a vital job in a warming world and one that climate engineers are trying to emulate, Earle noted. (See pictures of seven emergency climate fixes.)

"What we do to the ocean, we're doing to our life-support system—we’re doing it to ourselves," Earle said.

Oil Always Wins

Standing in the warm, calf-deep water of the bird refuge, the National Wildlife Federation's Schweiger pointed out that the marshes of the Gulf Coast replenish the entire ecosystem, for instance by protecting shorelines from eroding.

If exposed to oil, these Louisiana wetlands—which human development has already diminished by 40 percent—may wither away, leaving just the open ocean.

And that means the noisy shorebirds nesting just a few hundred feet behind him would have to find another place to go.

"When oil collides with wildlife," Schweiger said, "oil always wins."