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FallNott Memorial 2012

Heavy metals found in Gulf of Mexico oysters

Left: An eastern oyster shell Right: David Gillikin stands beside the inductively coupled plasma mass spectrometer, a machine he uses to analyze shells like those in his hand.

ysters, if you’re a fan, are delicious any which way— on the half-shell, steamed, stewed, slathered in cocktail sauce. But when David Gillikin (incidentally a big oyster fan) gets ahold of these mollusks, he’s not shucking them at the kitchen table.

The assistant professor of geology is part of a team that’s studying the bivalves in the Gulf of Mexico. Their findings indicate that eastern oysters (Crassostrea virginica) have more heavy metals in their shells and tissues than they did before the 2010 Deepwater Horizon catastrophe, which caused the largest offshore oil spill in U.S. history.

Gillikin and Damon Byrne ’11 conducted all the geochemical analysis on the shells and tissues with a specialized machine, an inductively coupled plasma mass spectrometer. And while the levels of vanadium, chromium, cobalt and lead they discovered are extremely low, their presence is noteworthy.

“One of the reasons we’re analyzing these materials is to see if the base of the food web—phytoplankton—is incorporating metals from the oil,” Gillikin said.

This tiny, plant-like organism is a primary food of oysters, and if oysters contain heavy metals, it is probable phytoplankton does too.

“This has the potential to further biomagnify up the food web to potentially higher and possibly damaging concentrations in wildlife,” Gillikin explained.

While he and other scientists don’t currently know exactly how trace metals like these move through the food chain, or how long they persist, or how they might impact the health of higherlevel predators—like large fish—the team’s work has already shown the oysters aren’t in prime shape.

Eighty-nine percent of post-spill oysters in the study have irregular gill tissue, the cells of which have become flattened. And flattened cells, as opposed to normal columnar cells, have less surface area available for respiration and filtering phytoplankton from the sea.

“While not fatal, this impact will probably lead to reduced respiration and cause the animals to be stressed,” Gillikin said.

And stress could possibly reduce oyster reproduction, which might mean less food for crabs, starfish, mackerel, and other predators. At this point, however, the overall, long-term health of the oysters—small barometers of the overall, long-term health of their environment— remains unknown.

“Our data is still too preliminary to draw any conclusions about the general well-being of the Gulf of Mexico,” Gillikin said.

Eventually, though, the team does hope to clearly show how heavy metals are impacting this valuable natural resource. Gillikin himself wants to use his analyses of oysters, post- and pre-spill (sometimes going back as far as the 1800s using shells from museums), to create a sort of ecologic health record.

“A second reason for this work is to determine if we can use shells as archives of oil spills, which would allow us to develop a detailed history of oil pollution in the Gulf and elsewhere,” Gillikin said. “The Gulf has experienced natural oil seeps for millennia and many spills since drilling started, though the BP spill is clearly the largest.”

“If we can understand how natural seeps and the oil industry have impacted the region at different points in time,” he added, “we can tell if the industry is changing things environmentally.”

Such information would benefit both the Gulf and the people who depend on it.

“Oysters alone are highly important to the Gulf Coast fishing industry,” Gillikin said, “accounting for $60.1 million in revenue in 2008 alone.”

Gillikin’s collaborators on this study are lead researcher Peter Roopnarine, California Academy of Sciences; Deanne Roopnarine, Nova Southeastern University, Florida; Laurie Anderson, South Dakota School of Mines and Technology; and David Goodwin, Denison University, Ohio.

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