Environmental Protection

Study Findings Boost Support for Using Oysters to Clean Chesapeake Bay

Biologists at Virginia Commonwealth University found that an additional 2.5 centimeters of growth allowed a farm oyster to remove 2.2 times the nutrients of a regular oyster.

The Chesapeake Bay is the largest estuary in North America, and although many efforts have been taken to improve its water quality, nutrient pollution still keeps it at unacceptable levels. Chronic water quality problems caused by agricultural and urban runoff, municipal wastewater, and atmospheric deposition from the burning of fossil fuels lead to oxygen depletion, loss of biodiversity, and harmful algal blooms.

In a study funded by the U.S. Environmental Protection Agency and administered by the National Fish and Wildlife Foundation, biologists at Virginia Commonwealth University measured the nutrient removal capacity of the Eastern oyster, Crassostrea virginica.

Researchers found that an additional 2.5 cm of growth allowed a farmed oyster to remove 2.2 times the nutrients of a regular oyster. In fact, a large-scale oyster farm harvesting 1 million of these 76-mm oysters can remove 132 kg of nitrogen, 19 kg of phosphorus, and 3,823 kg of carbon. The full study is available in the January/February 2011 issue of the Journal of Environmental Quality.

Oysters were a novel yet obvious choice to enhance the ecosystem’s water quality. They process nutrients while feeding on phytoplankton, and then store the nutrients in their shells and tissue through a process known as bioassimilation. Although the Chesapeake Bay is a natural habitat for the Eastern oyster, 99 percent of the native population has been lost, prompting researchers to explore the use of commercial oyster farms.

Oysters were raised at two commercial-scale aquaculture sites in Chesapeake Bay as well as a site in Maryland and one in Virginia to represent two typical cultivation environments in the bay. The nutrient contents of the tissues and shells of oysters of various sizes were measured.

According to Colleen Higgins of Virginia Commonwealth University, “Based on these results, it would take eight large-scale oyster farms harvesting one million (of these) 76 mm oysters per year to remove one ton of nitrogen from the bay, providing managers with the ability to determine the practical implication of such an ecosystem service.”

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