By Mike Di Paola, Bloomberg News

September 27, 2007

Steve Patterson stoops down on the dock and picks up a floating cage about the size of a lobster pot from Quonochontaug Pond in Charlestown, Rhode Island. He removes a bag to point out the dark patches clinging to the shells. These are baby oysters, known as spat. ``Look at that -- some are as big as your thumbnail,'' he says.

Even when they grow big enough to eat, these pampered shellfish will never hit the raw bar. Patterson, who is coordinator of the Rhode Island Oyster Gardening for Restoration and Enhancement program at Roger Williams University in Bristol, Rhode Island, is breeding the mollusks to help clean up the nation's waterways.

Oysters are naturally efficient at filtering silt and nutrients, particularly the excess nitrogen from agricultural runoff. When nitrogen concentrations get too high, oxygen is depleted from the water, creating dead zones. Patterson hopes to create vast populations of Crassostrea virginica, the Atlantic oyster, throughout the waters of Rhode Island. ``Oysters have an incredible ability to clear a lot of water of any particulate matter,'' says Patterson.

An adult oyster can filter up to 50 gallons of water in a day, taking out not only nutrients but plankton and other silt. This process clears the water and allows sunlight to penetrate deeply, photosynthesizing the aquatic plants.

Baby-Sitting Bivalves

Last year the university's hatchery began seeding salt ponds and Narragansett Bay with spat, planting half a million oysters in coastal waters, where volunteers baby-sit the growing bivalves.

The nurseries, scattered around the state's salt ponds and Narragansett Bay, are simple. A nylon bag is filled with about five pounds of clam shells, or cultch, which serve as an oyster bed. Half a dozen bags are placed in the floating frame and immersed in 8 inches of water; each bag can yield about 2,000 oysters, which can live as long as 30 years.

The volunteers, usually residents with shoreline property adjacent to a site, tend to the floating cages once a week, flipping the bags and flushing out the accumulated algae and fecal pellets that can foul the nest. By December, these juvenile oysters should grow to about an inch in diameter. Then they'll be moved to a designated shellfish restoration site.

The oyster isn't just an excellent janitor; it's a crucial component of the marine ecosystem. An oyster bed, like a coral reef, provides safe haven for small fish and other marine organisms that attract larger, sellable species, such as winter flounder, lobster and tautog. Remove the oyster and the entire food web might collapse.

Seed Money

Last year Patterson's program seeded 18 sites with oyster beds, and there are now about 55 sites in all. Oyster beds are gaining mass in Bristol Harbor, the Sakonnet and Potowomut rivers, Point Judith and here in Quonochontaug. The seed money for the project was a pittance: about $35,000, from the Rhode Island Aquaculture Initiative, a $1.5 million program pushed through by Senator John F. Reed, the Rhode Island Democrat, in 2002.

The Rhode Island project is the brainchild of Roger Williams's biology professor Dale Leavitt, who says he was ``pushed into it'' by the area's commercial shellfishermen.``They saw it as being beneficial to their industry,'' Leavitt says, because the oyster nurseries and their attendant volunteers also can educate the public on what aquaculture is all about.

The idea of cleaning water naturally is an appealing one. Connecticut, which has a $70 million aquaculture industry, is also considering a similar mollusk program in Long Island Sound, where there's already a thriving commercial oyster business. Seeding the sounds with enough oysters to improve water quality could only be good for business.

Unintended Consequences?

Still, tinkering with nature can cause unintended consequences. ``One concern is that if you create these oyster reefs that aren't harvested, they could become a source of disease,'' says Mark Tedesco, director of the U.S. Environmental Protection Agency's Long Island Sound office, which is evaluating a seeding program.

In recent years, the gravest threat to the Atlantic oyster has been the spread of parasitic diseases, such as the ones that decimated populations in the Northeast in the 1990s. ``Oyster reefs could actually be incubators for these organisms,'' Tedesco says. He adds that while aquaculture can help control nutrients in the water, it should complement other management strategies, such as land-based controls on agricultural activities.

Epidemic Survivors

In fact, the seeds used for the Rhode Island program are progeny of the resilient specimens that survived the epidemics of a decade ago. Though Patterson's first generation of offspring are being raised in clean water, this year the state gave him permission to seed the dodgier waters of the Kickemuit river in northern Narragansett Bay, which the state designates as ``conditional.'' Patterson hopes eventually to expand the program into even more polluted areas.

Is there any downside to reintroducing the oyster to its historical habitats around the Northeast? True, more oysters would probably also attract more of their natural predators, such as starfish, but that's a small price to pay for cleaner water. Oysters in New York Harbor were once so plentiful they could filter the entire harbor in a matter of days, thereby maintaining a most fecund environment. Those are the demographics nature had intended all along.

(Mike Di Paola writes about preservation and the environment for Bloomberg News. The opinions expressed are his own.)