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Right Now | Intervention with teeth--and mussels

Oyster Environmentalists

January-February 2005

Once so degraded that residents avoided touching the brackish water, the 106-acre Wilson Bay in Jacksonville on the North Carolina coast now hosts a healthy cross-section of aquatic life. From the microscopic creatures at the foundation of the bay's food chain to golden eagles and ospreys—the local "keystone species" whose populations determine the health of many other species in the ecosystem—wildlife has returned to a basin where municipal wastewater used to be discharged. There are still miles to go in the bay's evolution from polluted to pristine, but the process shows great promise thanks to a mélange of approaches, beginning with the introduction of a bivalve—the oyster.

Wilson Bay's journey began in 1998 when Jacksonville's governing council, concerned that its water-based waste-processing plant would be forced to close due to ever-stricter standards for wastewater discharge, shut the facility down. In its place, the city created a land application system that stopped further effluent from being pumped into the bay. But there was no precedent for cleaning a body of water of such magnitude.

The bay—once home to abundant waterfowl, fish, and other aquatic creatures and a source of recreation for the area—had succumbed to a combination of tainted runoff from surrounding neighborhoods, creosote posts supporting a dock at a nearby military installation, and a 50-year buildup of urban effluent. The water had become so polluted that fecal coliform levels soared above the recreational standards set by the state.

Top: An aerial view of Wilson Bay near Jacksonville, North Carolina. Bottom: A sack of bay cleaning oysters.
Courtesy of Jay Levine

City officials asked veterinarian Jay Levine, M.P.H. '84, for ideas on how to resurrect the bay, situated at the interface of fresh and brackish water in the New River. Levine, a North Carolina State University College of Veterinary Medicine researcher, had recently returned from a trip to France, where he studied oysters produced through aquaculture techniques. He devised a multilateral approach to Jacksonville's problem that combined seeding the water with bivalves such as oysters, clams, and mussels; enhancing the water's flow and increasing its oxygen level; restoring wetlands; and removing the polluting posts.

Bivalves filter many times their weight in water, combing it for edible detritus and other food. After consuming the food, they expel the water in cleaner form. Since one adult oyster can process several gallons of water a day, depending on its species, placing hundreds of bags filled with thousands of oysters in the water would have a positive effect over a period of time.

Critics of the strategy believed that the bivalves could not do the job and would not survive in the bay, due to its fluctuating salinity levels and the presence of harmful organisms that could overwhelm the young oysters. Levine nevertheless persevered, using an oyster native to the area. To increase their odds of survival, he had the oyster spat placed in flat plastic cages suspended a few inches below the surface, where they could use surface oxygen. When the oysters grew, they were moved to tubular mesh bags suspended with floats and spaced a bit farther apart, but still near the water's surface. Although their initial growth was slow, the oysters survived.

To enhance water movement and prevent stratification, leading to too little oxygen at lower depths, Levine and his associates used aeration units to strengthen circulation. Within months, the thriving oysters helped reduce the concentration of organic particles on the bottom of the bay. "Oysters were only one small part of this project," Levine says. "We used them to kick-start the recovery process."

As the first link in the food chain—the "benthic community" of organisms living in and on the ocean floor—gained a foothold in the bay, successive links also strengthened. Crabs, shrimp, and mussels reappeared. Reestablished wetlands further enhanced water filtration, and environmental engineers were hired to design stormwater filtration systems and implement other changes to divert excess nutrients from moving into the bay and overstimulating aquatic plant growth.

Within two years, ducks, geese, cormorants, pelicans, and herons began to frequent the bay. The waterfowl nested in the carefully restored wetlands that ring the bay and fed off the many species of fish that reappeared after decades of absence. "At first, we'd go out and see one duck," Levine says. "Now it's alive with waterfowl."

Although far from complete, early project results have been encouraging. The park along the bay's banks once stood empty, reeking from the stench of filthy water. Now families picnic at the waterside and the bay hosts boating, fishing, and a kaleidoscope of wildlife. And scientists in places as far away as Torino, Italy, have begun to clean their own polluted waterways using the multifaceted, integrated process Levine and his team applied at Wilson Bay.

~Carole Moore

 

Jay Levine e-mail address:
jay_levine@ncsu.edu