Oysters belong to a group of organisms known to biologists as filter feeders or suspension feeders: they take in water, filter out their nourishment, and expel what they don't need. In many cases, oyster waste becomes another aquatic animal's food.

Scientists
believe that 200 years ago, the filtering action of oysters actually cleaned the entire volume of the Chesapeake Bay in less than a week! Today, because there are far fewer oysters and far more sediments and other pollutants that need filtering, this same natural process may take more than a year.

Click on the image below to hear more about the water cleansing function of oysters and their value to the ecosystem of the Chesapeake Bay.

In the late 1800s, 10 to 15 million bushels of oysters were harvested every year from the Maryland waters of the Chesapeake Bay, but by the early 1990s, the annual haul had dropped to around 100,000 bushels--a tiny fraction of what was taken a century before. Over-harvesting was a big problem a hundred years ago-but the biggest problems today are actually caused by diseases.

The Oyster's
worst enemy today is a disease known as Dermo, caused by a very tiny protozoan parasite. Scientists at the Estuarine Research Center are among the many researchers trying to learn just how dermo attacks oysters and how long it takes to kill them once it takes hold.

The research begins with healthy young oysters placed in various parts of the Patuxent River. "We harvest some of the oysters every month and check them to see whether they have contracted dermo or not," says George Abbe, ERC senior scientist.

Click on the image below to hear Mr. Abbe describe how ERC researchers are using healthy oysters to learn more about the deadly Dermo disease.

Oysters may take up the infection in their first year of life, but research indicates that the infection generally doesn't prove fatal until the oyster is a little bit older. "We know that the oyster continues to feed and eat," says Brian Albright, who works with Abbe on the dermo research, "but somehow the disease inhibits the oyster's ability to store glycogen or fat." In time, the disease becomes a huge drain on the metabolic system of the oyster. Even though it continues to feed, it's as though the oyster is starving to death.

"At some point the infection becomes so great that it simply overwhelms all of the oyster's systems," says Mr. Abbe. "The oyster just fades away." By examining oysters at various parts of their life cycle, Abbe and Albright hope to get a handle on exactly what conditions cause dermo to become lethal. Like medical researchers studying the impacts of cancer or HIV on humans, Abbe and Albright acknowledge that in order to have any hope of helping the oyster, they need a better understanding of the disease.