Oil Spill Wildlife Spotlight: Oysters

Culling oysters. Credit: Rob Warner (NOAA), Roger Fay (TDI Brooks)/NCCOS

Served fried, raw, or swimming in a cholesteric, creamy stew, oysters are a sea-foodie’s versatile delight. The Gulf region harvests about 67 percent of the nation’s pearly bivalves, making it the the largest oyster-producing region in the country. Louisiana is the nation’s top-producing state, averaging 12 million pounds of shuck meat a year, with an average dockside value of around $55 million (in 2008, however, it was $38.8 million).

As fate would have it, the recent oil spill has occurred right at peak spawning season for oysters across the Gulf, although Louisiana’s appear to be safe—at least for now. But if crude oil wends its way into the interior marshes where oysters make their beds, that could spell tragedy. “Inshore, marshes are nursery grounds for just about everything we know and love when it comes to seafood, except for tuna and other offshore species,” says John Supan, director of the Sea Grant Bivalve Hatchery on Louisiana’s Grand Isle. “If the oil comes in contact with [oyster] reefs, it gets in all the nooks and crannies,” he says, and “it can ooze out of there for years.”
If there’s a silver lining—for most of the oysters we eat, in any case—it’s that the spill occurred 50 miles offshore, so it will have some time to weather. In other words, some of the compounds in the oil that are toxic to oysters—such as polycyclic aromatic hydrocarbons, or PAHs—can rise off the surface of the water and into the air, before the oil reaches their nurseries.
The bad news is that hurricane season is on its way, and a storm could push inland the oil that’s currently at bay. “If you haven’t been to church lately, you’re going now [and] praying that we have another quiet hurricane season,” says Supan, also an associate research professor School of Renewable Natural Resources. 
Of course, inundation by crude oil is just one potential problem. Another entails oysters’ contact with dissolved oil, a more "invisible" menace. “What you can see is dangerous,” says Supan, but “there’s something that’s not visual that we need to understand.”

Oysters filter about eight liters of seawater an hour as adults, so whatever is in the water will occur in higher concentrations in their little bivalve bodies. They’re known as “sentinels of the estuary,” says Supan, because problems with water quality will generally first be noticeable in them before other marine organisms. And the chemical dispersants used to break up oil could reduce the spill’s exposure to weathering  (and hence loss of PAHs), leading to more dissolved oil (although, with some help from marine microbes, some of that will be naturally biodegraded).

Compounds like PAHs can become incorporated into lipids stored in oysters, ultimately resulting in abnormalities in their digestive glands, as well as reproductive problems in the gonads where sex cells are created. Tainted oysters that have just formed their shells are identifiable by a crooked hinge as opposed to a straight one in normal individuals.
For now, however, oyster lovers--and consumers--need not worry. What’s currently in the marketplace is fine to eat, and the National Oceanic and Atmospheric Administration's Fisheries Service is taking precautions by closing off certain areas to fishing based on current models of the spill. Still, a note of caution: Models are only correct if what they predict comes to pass—that is to say, if oil is found where they suggest it will be. “Models are only as good as the ground truthing,” says Supan. But at this point in time, the nation’s prime oysters seem to be in the clear. 
*this article was updated at 10:53 am, 5/18/10

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