Gulf of Mexico Oysters in the Gulf of Mexico consumed little, if any of the crude oil from the 2010 BP Deepwater Horizon oil spill that spewed nearly half a million tons of crude oil into Gulf waters, according to a recent scientific paper.

A study last year by University of New Orleans oyster biologist Thomas Soniat similarly found that oysters - at known oil-exposed sites in Louisiana - showed no contamination or apparent biological signs of exposure six months after the spill.

Since the oil spill, fishermen and consumers have been concerned about the status of the local fisheries, but, in terms of consumption, federal and state scientists have made it clear that local seafood is safe to eat. Still, despite all such assurances, questions inevitably have lingered.

"Often referred to as the worst environmental disaster in America's history, the Deepwater Horizon oil spill was expected to significantly alter the Gulf of Mexico marine ecosystem with potentially long-term effects to coastal and open waters," the Environmental Science & Technology paper published last month states. "In many cases, however, the extent and nature of effects have been difficult to quantify due to the physical setting, offshore application of dispersants, potentially rapid microbial degradation, and low detection rates for affected organisms.

"Additionally, much of the oil material that flowed from the well was natural gas and very light hydrocarbons that dissolved in the water column without entering surface waters of nearshore environments."

Alabama’s Dauphin Island Sea Lab marine scientist Ruth Carmichael and her colleagues found in the paper that while oysters may have been exposed to oil, they actually consumed very little, if any, in their diets.

The authors make clear though that their findings are "not an indication that oysters were not exposed to oil; rather it implies that oysters either did not consume oil-derived materials or consumed an insufficient quantity to be clearly detectable against the background of their natural food source."

Carmichael and her colleagues - who included Edward Overton with LSU's Department of Environmental Studies - were able to use Gulf of Mexico oysters sampled before, during, and after the spill to define how the oysters’ diet changed due to the oil spill. Oysters are filter feeders that remove particles from the water so that their shell and soft tissues reflect local environmental conditions.

Carmichael said that she and her colleagues are not sure whether the local oysters simply avoided eating oiled material in their surrounding or whether there simply was not much oiled material around them.

"What we do know is that the natural background diet was the dominant food source to the oysters we tested before, during, and after the spill," Carmichael said.

While oysters typically slow or cease feeding under stress, the authors note in the paper that their findings also "suggest that oyster feeding and subsequent growth was not significantly affected by potential oil exposure."