Gulf oil spill: Not as bad as we first thought?

"Right now, the body count on the spill is pretty minimal," Dr. Shirley acknowledges, referring to the number of fish, birds, and marine mammals known to have died from contact with oil. But he says he expects the number to rise significantly as researchers conduct follow-up studies.

"We know from Prince William Sound that only a very small percentage of the oiled animals ever made it to the surface," he says, referring to research conducted in the aftermath of the Exxon Valdez spill in Alaska in 1989.

"With Exxon Valdez we didn't find out the full effects of the spill – and we still don't know all of them – until years after the spill had been cleaned up and the Rush Limbaughs of the world were telling us it was pristine again," he says.

Marine organisms that are likely to take the biggest hits are large and reach reproductive maturity at a relatively late age, Shirley says. These include turtles and marine mammals such as porpoises and whales. And most of these will never reach shore, but sink as they succumb either to the direct toxic effects of oil or through indirect effects, such as compromised immune systems, he says.

That said, "I never was a doom-and-gloom guy; I know that the Gulf will recover," he adds. "Many of the commercially important species will rebound rather quickly," particularly shrimp and oysters in least-affected oyster grounds.

Underwater unknowns

Concerns continue to surround the enormous amount of oil remaining thousands of feet below the surface. There, it's much harder to measure, track, and even attribute effects to the oil and methane scientists have detected.

The deep-sea ecosystem is used to dealing with natural oil seeps known to dot the bottom. But the impact of millions of barrels of atomized oil, methane, and dispersant at those depths are poorly known.

One of many aspects scientists are eager to track is the effect of the oil on the amount of oxygen in the water.

Scientists have detected low oxygen levels within the subsea clouds of oil and methane they've detected so far. But the low levels are still significantly higher than the levels needed to declare the water "hypoxic."

Bacteria consume oxygen to break down the oil and methane. Between the cold temperatures at those depths, and the bacteria's own needs, the already-slow breakdown process could decelerate further, some researchers suggest.

To this point, no one has been able to put numbers to the amount of oil microbes may have eaten, notes Samantha Joye, a marine scientist at the University of Georgia who has been leading a team of undersea plume hunters. Nor, she says, does anyone know whether bacteria break down the dispersants.

Indeed, throughout the blowout, researchers have pointed to the almost overwhelming list of unknowns in an unprecedented off-shore oil accident.

Thus, even for those who use past experience to foresee the Gulf's recovery, it's a cautious optimism.

"There's going to be a big damage-assessment study of this spill over the next 10 years," says LSU's Overton. "But if my assessment is close to right, it means our environment will come back fairly quickly and people's lifestyles will not be wiped out, that they'll be able to make a living off the northern Gulf and enjoy the recreational benefits of this body of water. We'll have to see."

Staff writer Patrik Jonsson contributed to this report.

Related:

• New Gulf oil spill mystery: How much dispersant did BP use?
• EPA scolds BP in Gulf oil spill: dispersant is too toxic, change it
• Gulf oil spill: The story so far

IN PICTURES: The Gulf oil spill's impact on nature

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