Study: Farmed Oysters Can Help Clean the Chesapeake

Now that native bivalves are nearly gone, farmed variety could bring some relief

Oysters have been the source of one of the Chesapeake Bay’s most valuable commercial fisheries for more than a century. Over the decades, the bay has lost more than 95 percent of its native oyster population and, in an ironic twist, a new report says introducing farmed oysters could help clean it up.

The study, funded by the U.S. Environmental Protection Agency (EPA), was conducted by researchers at Virginia Commonwealth University (VCU). They concluded that oyster aquaculture could produce meaningful results.

“Based on these results, it would take eight large-scale oyster farms harvesting one million 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,” said Colleen Higgins, of VCU.

In the late 19th century, the native oyster population could filter a volume of water equal to that of the entire Bay every three to four days. Today’s depleted population takes nearly a year to filter the same volume.

Scientists attribute the decline of the Bay’s oyster population to a combination of several factors, including:

• Historic fishing practices;
• Oyster diseases;
• Loss of habitat due to pollution from excess nutrients and chemical contaminants;
• Sedimentation from forest removal, and development and agricultural runoff.

Oysters process nutrients while while feeding on phytoplankton. They store the nitrogen in their shells and tissue through a process called bioassimilation.

According to EPA estimates, significant water quality improvement would require the bay’s watershed states to reduce the amounts of nitrogen getting into the bay by about 63 million pounds annually. Therefore, the impact of eight oyster farms likely would be minimal.

The study said aquaculture could be meaningful if it is used in targeted areas, such as coves. It follows a study by the Chesapeake Bay Foundation which concluded that the bay is showing signs of recovery, but is still struggling with pollution from farms, sewage treatment plants, urban and suburban streets, parking lots and lawns.

A day after the Foundation’s report, the EPA established a 200-page “pollution diet” for the bay which spelled out steps that Maryland, Virginia, West Virginia, Pennsylvania, Delaware, New York and the District of Columbia must take by 2025 to put the nation’s largest estuary on the path to recovery.