More than 40 years before BP’s catastrophic oil well blowout in the Gulf of Mexico, the barge Florida ran aground in Buzzards Bay one foggy night and dumped nearly 200,000 gallons of fuel. The effects of that accident still linger in the marsh mud around West Falmouth.

So while the news yesterday that the oil company thinks it may have succeeded in stopping the flow of oil into the Gulf is welcome, it by no means signifies the end of the matter.

The environmental and economic effects of what federal authorities now say is by far the largest oil spill in American history will be felt for decades; of that Dr. John Stegeman, senior scientist in the biology department and director of the Woods Hole Center for Oceans and Human Health, has no doubt.

“The oil in the Gulf, certainly, without question, will continue to have long-term biological and economic and social effects,” he said.

And he should know, on the basis of 40 years of intimate knowledge of the West Falmouth spill, and years spent studying how contact with toxic chemicals, particularly oil, affects the function of molecular processes in cells of organs and tissues, and how that differs among species.

“One of the first [spills] to be intensively studied was the one in West Falmouth,” Mr. Stegeman said. “That led to a lot of research on oil pollution here at the Woods Hole Oceanographic Institution. I got involved in oil research when I came here as a postdoctoral student. So we know a lot about what happens when oil and animals get together.”

On the basis of that knowledge, he said, they can predict, to a certain degree the long-term future of those marshlands in Louisiana which already have been oiled, and other coastal areas which may yet be affected by the vast quantities of oil which continue to drift in the waters of the Gulf of Mexico.

And one thing they can safely predict is that you can never, ever get all the oil out, once it gets in.

“Some of the hydrocarbons continue to persist 40 years later in those West Falmouth sediments,” said Dr. Stegeman’s WHOI colleague Judith McDowell, senior scientist in the biology department.

And that still has ecological consequences.

“There are cleaner sediments on top, but as burrowing organisms try to penetrate those sediments, they will not go past that hydrocarbon barrier,” she said.

“A graduate student a few years ago studied populations of fiddler crabs, and found they were more prone to predation because their burrows were shallow, because of the contaminated sediments.

“There were other effects, too. Behaviorally, they acted as if narcotized, almost like drunken sailors.”

Indeed it was about a decade after the West Falmouth spill before fiddler crabs came back to the affected areas at all.

“Effects like behavioral change, physiological change, population change can take a long time to recover,” she said.

Of course, fiddler crabs don’t matter to the economy. But other crustaceans do, like lobsters in this part of the country, and shrimp in the Gulf.

Ms. McDowell pointed to the consequences of another, relatively minor oil spill in Rhode Island some years ago. That spill happened in mid-winter, and oil was trapped under ice, and the “trajectory models said it should present no problems, but it killed large numbers of juvenile lobsters,” she said.

In a subsequent damages case, lawyers successfully argued fishermen should be compensated not just for the time immediately after the spill when they could not fish, but also for reduced catches in subsequent years because several year classes were not recruited to the population.

“Crustaceans are very sensitive, so it wouldn’t surprise me if some of the early developmental stages [of Gulf shrimp] would be affected by the BP blowout,” she said.

So Gulf shrimpers, like New England lobstermen, could face losses extending well beyond the immediate closure of their fishing areas.

Shellfish such as oysters and clams, being filter feeders, can accumulate a lot of hydrocarbons in them after a spill.

“Over time they will eliminate a lot of that, given a clean environment, but in terms of harvesting in areas like oyster beds or clam flats, those animals will not be harvestable for as long as the oil persists. In the West Falmouth spill, there was some recovery within a year or two,” she said.

The key words there are “given a clean environment.” The Gulf spill is, on the basis of the best estimates of federal authorities, twice as big as the Exxon Valdez spill in Alaska in 1989, and at least 100 times bigger than that in Buzzards Bay in 1969.

And while much may be predicted on the basis of scientific analysis of these past experiences, there also is much which is different and, at this stage, unknowable.

Buzzards Bay happened in shallow, cold water; the Gulf spill is in deep, warm water. Buzzards Bay happened on one day; the Gulf rig has leaked for more than five weeks. And the response to the Gulf spill has involved the use of unprecedented quantities of toxic dispersants

“It’s in a completely different environment,” said Dr. Stegeman.

“Where is that oil going to go, in what concentrations, how much is below the surface? There are reports of subsurface plumes that are neutrally bouyant. Where are they going, how are they impacting the fauna?”

“Certainly there will be effects in marshes and on beaches that will be visible. They won’t be able to harvest shellfish, for example, for a long, long time. Who knows when the oyster beds will produce oysters that are clean enough to eat?

“What we do not know fully well in this case is how animals at depth and in the mid-water may react to oil and the dispersants. Dispersants can make oil more available for uptake. They may alter the toxicity of the oil. The physical properties change so the oil can more readily pass membranes and get into animals,” he said.

Dispersants, said Ms. McDowell, can actually result in filter feeding organisms ingesting more toxins than they otherwise would have.

So why are they used?

“Dispersants can act to render the environment evidently, to the observer, less contaminated. They can also, perhaps, help render the oil into a state that makes it more readily attacked by bacteria,” said Mr. Hegeman, who noted that there are natural undersea seepages of oil — sometimes in huge quantities — which some life-forms have evolved to digest.

But that could bring its own problems, too.

“When bacteria attack oil for energy, they use oxygen to do that. There is concern this could make an area where there already is, on a seasonal basis, a severe problem with low oxygen levels in the water, that may aggravate the situation and make a large region perhaps anoxic.”

Other life forms, too, can metabolize oil.

“You, me, fish, whales, turtles, when we have exposure to the chemicals they turn on molecular machinery to degrade that oil.

“Some fish can do it fast enough that after a couple of weeks, you often can’t detect them unless you use very sensitive detection methods,” he said.

“Fish in the deep ocean do show the ability to mount this enzyme response that can help degrade the chemicals. I can’t tell you how they will all cope. We don’t know much at all about animals in the deep ocean.

“But that [metabolic process] is not without risk, because often the metabolism of a hydrocarbon can result in an intermediate product on the way to elimination [a carcinogen] that is more hazardous than the oil hydrocarbon itself,” he said, continuing:

“In the marshes, the oil will certainly persist unchanged, for decades. So if you disturb, the sediments, it is released. That, in the future may produce severe toxicity. We don’t really know.

“We do know that 25 years on [from the Buzzards Bay spill] there were still changes you could attribute to oil, in some fish of the marshes.

“Those include increased levels of enzymes that metabolize oil.”

But in deep water, who knows?

“The issues are where the oil will move, at what concentrations, and how long will organisms be exposed, and the nature of the chemicals involved and how different animals involved will react. Those are variables,” Mr. Stegeman said.

And once the initial rush to shut off the oil is over, the scientists at WHOI stand ready to bring their expertise and their technology to bear in understanding the consequences, and where possible helping to mitigate them.

In essence, what BP and its subcontractors have done, is start a huge, uncontrolled experiment in the Gulf of Mexico, which scientists like those at WHOI and elsewhere will be studying for decades to come.