Oysters are critical to the health of estuaries along the Gulf Coast. As filter feeders, they clean water and cycle nutrients throughout the food chain, Florida State Marine biologist David Kimbro said in a June 1 statement.

"Having been decimated by historical overfishing, disease and poor water quality, natural oyster reefs are now the most degraded estuarine habitat worldwide, with only about 15 percent of global oyster reefs remaining," he said. "Unfortunately, here in the United States, we've eaten and dredged away most of the oyster habitat."

The oil spill could worsen the problem, said the University of South Alabama's Carmichael. Not only can oil affect the survival of oysters directly, it can also decrease the amount of available oxygen in the water column.

"We certainly know that the effects can be absolutely immediate," Carmichael told OurAmazingPlanet. "How long that actually affects overall growth and survival of the oysters is what we need to find out."

Gulf Oil Spill: Animals at Risk