Nutrient levels a growing worry for shellfish industry

The Fish Site
by The Fish Site
8 March 2007, at 12:00am

US - The commercial shellfish industry has more than a passing interest in the nitrogen and other nutrients entering South Sound.

As evidence mounts that increased nitrogen in the water from septic systems, stormwater runoff, lawn fertilizers and the like feeds algal blooms that, in turn, die and rob the water of oxygen, South Sound shellfish growers say they’re feeling pinched in several ways.

South Sound is home to roughly half of the state’s $100 million-a-year shellfish harvest. But it’s also home to a summer die-off of oysters in recent years that has reached 50 percent to 60 percent in some growing areas, including Eld Inlet.

A spike in the level of nutrients in South Sound appears to contribute to the summer mortality, stressing the oysters with too much food to eat at the same time they’re trying to reproduce, said Joth Davis, lead shellfish nutrition and genetics researcher for Taylor Shellfish, based in Mason County.

The increased algal blooms in the late summer also smother and suffocate clams, oysters and eelgrass growing in the intertidal zone, he said.

In some areas of South Sound, concerns over nutrient loading are more serious than the shellfish industry’s better-known, longstanding battle with bacterial contamination from failing septic tanks, stormwater runoff and animal wastes, Taylor Shellfish spokesman Bill Dewey said.

“Fecal coliform doesn’t kill the shellfish, and the sources of contamination can be corrected,” he said. “That hasn’t been the case with nutrients.”

As filter feeders, oysters, mussels and most clams capture and eat plankton and other particles suspended in the water. Historically, shellfish have been viewed as part of the nutrient pollution solution.

“Shellfish perform functions in the coastal ecosystem similar to the role that kidneys play helping to filter and regulate the flow of blood in the human body,” according to a 2003 paper on shellfish ecology prepared by the Puget Sound Action Team.

But a number of waterfront property owners living close to South Sound shellfish-growing operations are singing a different tune, suggesting aquaculture contributes to the nutrient problem, and disrupts the marine ecosystem.

Source: The Olympian