Spill could devastate U.S. Gulf Coast oyster reefs

MOBILE, Alabama (Reuters) - The lowly oyster, a tasty delicacy to seafood lovers but a curiosity to more squeamish diners, is also the backbone of marine life along the U.S. Gulf Coast and among the most vulnerable creatures now threatened by a giant oil spill.

The region’s oyster beds are the vital foundation of a commercial and recreational fishing industry -- including shrimp, crabs and other shellfish -- that generates $6.5 billion in annual revenues, according to one recent estimate.

The networks of reefs built up in shallow waters by these unassuming bivalves are like the Gulf of Mexico equivalent of the Caribbean’s coral reef system, only with oysters at the base of the pyramid instead of live coral.

In addition to providing shelter and food for a complex web of undersea species, the way coral reefs do, oyster beds serve a number of other important functions by virtue of their proximity to land.

“It is not only the economic engine of this region, it is a real indicator of the environmental and ecological health of the Gulf Coast area,” said Jamie Rappaport Clark, executive vice president of the conservation group Defenders of Wildlife and former head of the U.S. Fish and Wildlife Service.

Oyster beds form undersea breakwaters that buffer shorelines and wetlands from erosion due to storm surge, helping preserve a habitat for birds and land animals. At low tide, exposed oyster banks themselves offer a feeding ground for some birds.

And as filter feeders, oysters constantly strain the water of impurities for the estuaries, bays and marshlands that lie behind them, a characteristic that also makes the oyster reef particularly sensitive to contamination.

Gulf fishery managers are bracing for the arrival of oil gushing from a ruptured undersea wellhead off Louisiana’s coast since April 20, when the Deepwater Horizon drilling rig under contract with BP Plc exploded. The blast killed 11 crew members, sank the rig and unleashed a spill that could eclipse the 1989 Exxon Valdez disaster in Alaska.

The spill comes at a particularly bad time for oysters, coinciding with the peak season for oyster “spat,” the release of billions of tiny juvenile oysters the size of pepper flakes into the water, where they drift until those that survive settle onto a reef, attach themselves and grow to adulthood.

The Gulf’s oyster beds are “getting ready, like all other fisheries, to suffer a significant assault in the coming weeks,” Clark said. “And these filter feeders are the first lines of impact.”

A MARINE ECOSYSTEM MOST UNDER THREAT

Various seabirds, like the brown pelican, which was taken off the endangered list last year, and five species of endangered sea turtles, all just starting to nest in the area, also are at high risk and are more visible to the public.

But oysters are likely to be the region’s great unsung victims, whose destiny near the bottom of the food chain will be registered throughout the Gulf Coast marine environment.

Although decades of water pollution, much of it runoff from farms, storm sewers and industry, has taken a toll on aquatic life along the U.S. Gulf Coast, the region still is home to the world’s last, largely intact network of oyster reefs.

Compared with other types of marine ecosystems, oyster reefs on the whole are considered by scientists to be the most environmentally damaged globally, declining by 85 percent over the past several decades.

The Chesapeake Bay along the U.S. Eastern Seaboard, for example, has lost 99 percent of its once-bountiful oyster beds, said Mike Beck, a senior marine scientist for the environmental group Nature Conservancy.

With over half of its reefs still left, the Gulf Coast is the world’s “last, best” chance of maintaining a healthy oystery, Beck said.

The Gulf Coast leads U.S. commercial oyster production, accounting for nearly 70 percent of a total national catch valued at $131.6 million in 2008, the last year for which government figures are available.

With the oil slick taking longer than first expected to reach the main coastal areas, fish and wildlife agencies have scurried to cordon off the most ecologically sensitive areas with containment booms they hope will minimize the damage.

In Alabama, the spill poses a serious setback to efforts to enhance oysteries and other marine resources.

The state recently launched an ambitious restoration program that includes temporary closure of its publicly owned oyster reefs and the relocation of 6 million pounds of oysters from upper Mobile Bay to other areas, said Chris Denson, a marine biologist at the state Conservation Department.

Separately, the Nature Conservancy secured nearly $3 million in federal economic stimulus money to fund a pilot program to test three kinds of artificial reef structures along a salt marsh island near Mobile Bay.

The project was more than half complete when it was put on hold due to the oil spill.