And on a 10-point "Environmental Sensitivity Index" used by scientists, Tunnell said the beaches fouled by the Ixtoc spill rated a three. The Louisiana marshes, home to shrimp, crawfish and smaller marine organisms, get a 10 -- the top of the scale.
Joel Kostka, a professor of oceanography at Florida State University, may be able to reconcile conflicting views, and his answer is -- it depends. He studied the rocky Alaska shorelines fouled by the grounding of the Exxon Valdez in 1989, and is now studying the beaches of the Gulf.
Among other things, he said, critical factors are whether microorganisms can get to the oil, and whether they have a supply of oxygen to help do the job.
"When microbes have access and oxygen, oil will be degraded in days to months," he said in an e-mail. "When oxygen supply is limited or the oil is congealed or not dispersed (tar balls), oil compounds are likely to persist in beach soils for decades."
In the cold climate of Alaska, Kostka said 10 percent to 20 percent of the oil spilled from the Exxon Valdez is still there, buried in soil beneath the rocks on hundreds of miles of shoreline. On the hot beaches near the Ixtoc 1 site, nature has been much more active in breaking down the oil.
The same is likely to be true on the coastlines near the Deepwater Horizon, all three scientists said. White beaches, open to the air and the elements, are likely to recover fairly quickly.
Muddy marshes, on the other hand, could be in deep trouble, since oil will sink into the muck where it is effectively sealed off from the elements that would break it down.
Even Tunnell, who documented the recovery from Ixtoc 1, said he is more worried this time. He said he is uneasy about the use of dispersants a mile beneath the water's surface. And he's worried about deep-water coral reefs in the Gulf, which were unknown to researchers 30 years ago.
"We've insulted the Gulf a lot in the last 30 years," he said. "We've overfished it, and we've drilled a lot of wells. Its resiliency may not be as great as 30 years ago."