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Nature
Heroes on the Half-Shell
A growing number of conservationists see oysters as a key component to coastal restoration.

Oysters aren’t only excellent for slurping down with a dab of cocktail sauce; they’re also good for restoring ecosystems. Along the U.S. coasts, scientists and conservations are increasingly looking to oysters to help filter water, bolster species diversity, and prevent erosion. “Oysters become an important part of any restoration effort,” says Martin Posey, a biology and marine biology professor at the University of North Carolina at Wilmington.

Small-scale restoration projects that incorporate oyster aquaculture are currently under way in 15 states, including New York, North Carolina, Louisiana, and Washington. Federal, state, and local governments, along with nonprofit conservation groups like The Nature Conservancy, the Chesapeake Bay Foundation, and Massachusetts Audubon, are funding the programs—and seeing some promising results. 

A century ago oysters covered extensive sections of both the Atlantic and Pacific coasts. The formed massive reefs, often protruding from the water at low tide; in one case, off Long Island, a lighthouse was built directly on top of one such reef. Oysters became increasingly desirable as food during the 1800s, and people plucked them from intertidal zones by the billions. Studies show that in Virginia and Maryland alone, oystermen harvested 20 million bushels a year in the 1870s. The practice proved to be unsustainable, and oyster numbers dropped drastically after a decade. Increased pollution, disease, and loss of habitat contributed to their decline. In Chesapeake Bay, populations today are only one percent of what they were at their peak.

The plummet in oyster populations, coupled with runoff into waterways of nutrients, such as phosphorus and nitrogen, from agricultural and development, have led to many unbalanced coastal ecosystems. Nutrient enrichment spurs the prolific growth of algae, which blankets the surface of the water and makes it look like pea soup. Those algal blooms subsequently block light from reaching the organisms below the surface and deprive the water of oxygen. In the most extreme circumstances, such conditions lead to dead zones, where no organisms can survive. The number of dead zones has doubled nearly every decade since the 1960s, according to a study published this summer in Science.

To reduce nutrient overload, some scientists are now reintroducing oysters to areas where they once thrived, an idea that conservationists put into action in the mid-’90s, says Robert Brumbaugh, the director for the restoration program at The Nature Conservancy. Oysters were a natural fit, considering how some species can filter up to 50 gallons of water a day and digest and absorb nitrogen in the process. “It’s like putting sheep out into an overgrown field,” says Bill Walton, a fisheries and aquaculture specialist at the Cape Cod Cooperative Extension and Woods Hole Sea Grant program.

Hauke Kite-Powell, a research specialist at the marine policy center of the Woods Hole Oceanographic Institution in Massachusetts, grew oysters in Waquoit Bay on Cape Cod, which suffers from excess nitrogen levels due to coastal development. He and his team found that the bivalves improved the water quality. “You could make a meaningful dent in nutrient levels in a bay by setting aside some reasonable fraction of it to shellfish aquaculture,” he says.

Oysters not only filter water, however—they promote species biodiversity as well. They’re keystone species, meaning they have a greater impact on other organisms in their ecosystem than one would expect based on their abundance. If oysters are removed from the environment, the whole ecosystem suffers. Conversely, when sunlight can penetrate water that’s clear and oxygenated, for example—thanks, in part, to oysters—other organisms can thrive. Sea creatures can also find refuge on oyster reefs, which help prevent erosion. “When you’re talking about restoring a system, you’re not just talking about restoring the water quality,” says Posey. His studies show that in some southeastern waters where oysters flourish, blue crabs, pink shrimp, and finfish prosper, too.

Shellfish aquaculture, however, isn’t a panacea for ravaged marine ecosystems. “I think they’re part of the solution, but I think you need to look at the sources of pollution,” says Walton.

Scientists are also studying how restoration methods can be done in concert with oyster harvesting. Advocates for collecting the shellfish say that it’s a natural complement to restoration and can also provide financial incentives for those projects. In areas where waters are too polluted, oysters can be unsafe to eat. Harvests must also be sustainable, says Brumbaugh. “Oyster reefs are some of the most imperiled of any ecosystem out there,” he says. “We need to treat these things as ecosystems and not just as hors d’oeuvres.”

Few, if any researchers think that coastal restoration projects that incorporate oysters will ever bring the mollusk’s populations and the nutrient levels of coastal waters back to what they were in the 1800s, but many are hopeful that with more projects, marine ecosystems will continue to improve. “We can do a tremendous job of restoring oysters and creating a system that supports a diversity of organisms,” says Posey.

 

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