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

Driving down Highway 23 last week in the southern Louisiana fishing town of Port Sulphur (map), David Ojeda could smell that something wasn't right. Turbulent winds over the approaching Gulf of Mexico oil spill were blowing strong odors inland, the 68-year-old shrimper suspects.

"Everybody's worried," he said Wednesday at the Port Sulphur harbor, which was filled to capacity with fishers rendered idle by the spill. "Nobody knows what will happen."

Unpleasant though it may be for those on the shore, that smell could be a sign of Mother Nature doing her own dirty work: It's the pungent scent of evaporating surface oil, which rises into the atmosphere and gets broken down by sunlight.

The joint federal-industry response team, led by U.S. Coast Guard Rear Adm. Mary Landry, has been attacking the growing slick with an arsenal of chemical dispersants, protective booms, and containment domes on the seafloor, among other techniques.

At the same time, the environment has been doing its own cleanup, which should not be ignored, experts say.

"Just like Rear Admiral Landry discusses her toolbox, nature has its own toolbox for responding to oil spills, whether it's evaporation or photochemical breakdown or dilution," said Christopher Reddy, a marine chemist at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts. "Collectively ... they can be quite effective."

Yet experts caution that nature's contributions to the recovery effort might be hampered by long-term environmental abuse.

"The resilience of nature is a key issue," said Sylvia Earle, a marine biologist and National Geographic explorer-in-residence. (National Geographic News is owned by the National Geographic Society.)

The U.S. Gulf Coast obviously has some ability to bounce back from ecological disasters, "or else there would be nothing left in the Gulf after many assaults with spills and overfishing and flow of toxins from" human activity in the Gulf states, she said. (See pictures of recovery in New Orleans after Hurricane Katrina.)

"As long as you've got a reasonably healthy system, then recovery of some sort can take place. The sad thing is that much of the Gulf is already severely degraded, and resilience is not what it used to be. Let's just hope we can back off with other pressures to allow recovery to take place."

Gulf Oil Spill Is "Butter" for Microbes

Evaporation in particular "is our friend right now," WHOI's Reddy said, since its benefits are both immediate and major.

That's because the lightest oil molecules—the first to reach the surface from the leaking deep-sea wellhead—also happen to be the most harmful to wildlife, he said. (See "Gulf Oil Spill Pictures: Ten Animals at Risk.")

Many of these light molecules are volatile chemicals known as aromatic hydrocarbons, and if they don't evaporate, they can dissolve into the water and be toxic to marine life.

Heavier oil still in the water gets broken into droplets or dispersed naturally though wind and wave action, allowing legions of microbes to move in for a feast.

Energy-rich oil "is basically butter" to these organisms, Reddy said. "Any self-respecting bacteria is going to want to eat it."

But oil-munching microbes are choosy: They go after the most simply shaped oil molecules first, because smoother shapes are easier to nibble on than more complex, jagged oil molecules.

In other words, Reddy said, the bacteria "start off with big stuffed shrimp and prime rib and fresh sushi and [then] go to the less and less appetizing compounds"—which drags out breakdown of the oil by weeks or months.

Oil in the Breadbasket

Still, there is a bright side when it comes to microbial action in the Gulf, said Stan Senner, conservation director for the Ocean Conservancy.

The region's warm and sunny climate means that more microbes can stick around for longer, as compared with the colder, darker conditions in Alaska, the site of the 1989 Exxon Valdez oil spill. (Related: "Exxon Valdez Anniversary: 20 Years Later, Oil Remains.")

But these kinds of microbes only work where they can breathe, Senner noted. Once oil becomes buried in oxygen-poor sediments, "microbial action can be very slow to nonexistent." (Related: "Gulf Oil Spill a 'Dead Zone in the Making'?")

And when oil gets trapped underground, it can stay for decades, according to Gregory Stone, director of Louisiana State University's Coastal Studies Unit.

For instance, on the Mississippi coast—where smaller oil spills have washed ashore in the past—researchers have found oil as deep as 20 feet (about 6 meters), Stone said.

If oil sinks into the soils of the Gulf's breadbasket—the marshes—there's nothing nature or humans can do to stop it, experts say—and that could present a toxic nightmare for small animals that live in the sediments and the larger creatures that eat them.

"I Don't Have Room for Any More"

The effects of oil seeping into Gulf marshes would be like losing an entire nursery of babies in a major hospital, said Barton Longman, a former oil-rig roughneck and now recreational fisher in Port Sulphur.

About 40 percent of U.S. seafood begins its journey in these nourishing marshes, said Longman, standing in front of his boat. He may use the craft for a new charter fishing business—if he sticks around.

After enduring a fire and three big hurricanes in nearly a half century here, Longman said he will leave if the Gulf oil spill proves catastrophic: "I'm full ... I don't have room for any more."