But scientists who spent the decade studying the Deepwater Horizon spill still worry about its effects on dolphins, whales, sea turtles, small fish vital to the food chain, and ancient corals in the cold, dark depths.
The gulf's ecosystem is so complex and interconnected that it's impossible to take any single part as a measure of its overall health, said
Some scientists say the recovery has been remarkable since those dark spring days in 2010, when oil billowing from the sea floor began killing wildlife and blackening marshes and beaches from
But major concerns remain.
Here's a look at how some key aspects of the ecosystem are doing.
DOLPHINS AND WHALES
“Initially, industry experts were saying, ‘The dolphins and the whales, they’re smart. They’re not going to swim into oiled areas,’" recalled
But cetaceans must surface to breathe, rising through oil that spread across more than 15,300 square miles (40,000 square kilometres) - nearly as big as
Lung disease and other ailments caused by the spill killed more than 1,000 bottlenose dolphins over several years, many of them in Louisiana's hard-hit
Whales almost certainly suffered similar oil-caused ailments but can’t be safely examined, Schwacke said.
“The toothed whales, sperm whales, Bryde's whales, right whales ... these populations which were somewhat in jeopardy prior to the oil spill have been declining 5 or 10% a year ever since the oil spill,” said
Going forward, some
FISH
How fisheries would survive was hard to fathom while slicks fouled estuaries where many fish spawn, but scientists haven’t found any widespread species die-offs, said
“Fisheries in the marshes where the oil came on shore have continued to flourish. Recreational fishing continues to be productive and a very popular activity even in
It's a different story farther out and deeper down, where small fish feed top food and sport fish such as tuna or grouper, as well as whales. Murawski, now a professor at the
Laboratory research has found that oil damaged fish larvae's developing hearts and bones, MacDonald said.
Future restoration projects include plans to get anglers to use equipment that would slowly lower reef fish they don’t keep, rather than simply tossing them back. Another project aims to find the best escape hatches for “bycatch” hauled up in shrimp nets, and persuade shrimpers to use them.
MARSHES
The oil turned tall marsh grass as black as cinders and sank into the muck across
“Once all the roots and so on disintegrate, the whole marsh surface, all the soil, is lost. Given the fact that there is rapid sea-level rise and the land is sinking, it’s almost impossible to recover,” said
GoMRI surveys found birds, snails and crabs back at pre-spill densities, Wilson said.
But the insects worry
Then her funding dried up, but in
The vast majority of oiled wetlands were in
DEEP CORAL AND SEA BOTTOM
Far below the surface, deep-sea corals can live hundreds of years, creating habitats for multitudes of creatures near the bottom of the food web. Because of the
Swaths of such coral were killed, and they grow so slowly — only a few millimeters a year — that it’s hard to imagine how they could be replaced, Boesch said. Researchers found that seven years later, affected but surviving coral were less healthy than unoiled reefs.
Before the spill, scientists didn’t know that deep-sea corals were severely hurt by oil dispersing in a plume far below the surface. They discovered that rising oil interacts with plankton and then “snows down from the surface and eventually lands," changing the chemical biology of the sea bed, MacDonald said.
“So these are things we’ve learned. And none of these are good things,” MacDonald said.
Scientists plan to study these deep habitats more extensively, including mapping the gulf's seafloor. To protect the fragile corals, money is being spent to develop techniques for growing and transplanting corals and installing buoys in some places to alert trawlers to the corals’ underwater presence.
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