Due to an editing error, an article Saturday about the role of oysters in controlling harmful algae such as Pfiesteria microorganisms misstated the view of three scientists. The three had spoken in another context, agreeing that Chesapeake Bay seafood appeared to be safe. They were Dr. Sandra E. Shumway of Southhampton College at Long Island University, Dr. Katherine Richardson of the Danish Institute for Fisheries Research and Dr. Patrick Gentien of the French Institute for Sea Research.
The Sun regrets the error.
Decimation of the Chesapeake Bay's once-abundant oyster population over the past century may have removed one of the bay's natural mechanisms for controlling organisms such as Pfiesteria piscicida, scientists say.
FOR THE RECORD - CORRECTION
Percy Donaghay of the University of Rhode Island Graduate School of Oceanography said yesterday that oysters are a kind of marine "grazer." They remove algae and other microscopic phytoplankton such as Pfiesteria -- and the nitrogen they contain -- from the water.
The oysters' feces are then processed by bacteria in bottom sediments. The bacteria convert the nitrogen to a gas and remove it from the ecosystem.
"They're the equivalent of sewage-treatment plants," said Roger Newell, a professor at the University of Maryland's Center for Environmental Science at Horn Point.
By nearly wiping out the Chesapeake's oysters, Donaghay said, humans -- and more recently oyster parasites -- have created a bay in which thenutrients stored in one-celled algae are no longer removed from the ecosystem when the algae die. Instead, they are left to be consumed by the next well-fed generation of algae.
Chesapeake is an Algonquian Indian word meaning "great shellfish bay." The bay was once studded with oyster reefs so large that they rose above the surface in places.
In the past century, over-harvesting has reduced the bay's oyster population by 99 percent.
The 1996-1997 harvest was about 130,000 bushels, down from annual harvests of 2 million bushels two decades ago.
Newell said oysters once were abundant enough to filter the bay's water in three to five days. Today it takes them 300 to 400 days.
The bay's waters are rich in nutrients, making them ripe for the growth and frequent "blooms" of a variety of phytoplankton. Some of those organisms can be expected to be harmful or toxic.
