The new oyster wars are different. They are being waged under water, not by watermen, but by marauding parasites against nearly defenseless oysters. These marauders are protozoans known as Dermo (Perkinsus marinus) and MSX (Haplosporidium nelsoni). These microscopic organisms have been devastating oyster populations throughout the Chesapeake Bay. This killing field is reflected in the commercial harvest. In the last five years, harvests have fallen so low their landed value is less than the sale price of a comfortable home on a waterfront property. Before this devastation their landed value amounted to millions of dollars.

So well-established is Dermo on the bay bottom, that even with good sets of oyster larvae, the chances of oysters reaching harvest size are slim to nonexistent. Why can't oysters defend themselves? Why can't they fight against Dermo and MSX as they have against other pathogens in the past? And on the other side, why are these protozoans so successful in escaping the defenses of the oyster's immune system? Can anything be done to halt the devastation that these diseases have been effecting?

Until recently few answers were forthcoming. Now, however, marine scientists in Maryland, Virginia and Delaware are making quantum leaps in some areas of understanding. One reason for the advances has been a Congressionally funded program of research on oyster disease. It is the near-demise of the oyster fishery that moved Congress to fund the Oyster Disease Research Program.

Research involves molecular studies on the interaction between the protozoans and the oyster immune system. It involves also the development of sophisticated techniques for monitoring the presence of Dermo and MSX. Attempts are also being made at breeding strains of oysters that may eventually be able to resist the attacks of these protozoans.

Many of these studies depend upon large amounts of Dermo. Because of recent breakthroughs, scientists now have the ability to grow Dermo in continuous culture in the lab, and in abundant quantities. Growing Dermo in petri dishes makes it possible to study its life cycle and how different environmental conditions (as salinity, temperature, heavy metals, chemicals, etc.) affect its growth and behavior.

Dermo did not appear in strength in the upper Chesapeake Bay until the 1980's. However, it has been in the Gulf of Mexico and other southern waters since 1950. Because southern strains of oysters have been subjected to Dermo for so long, these oysters may have devloped natural immunities that Bay stocks do not have. The assumption is that geographically separated oyster populations behave differently with regard to Dermo. Some are simply less susceptible.

To test that assumption, investigators will try to identify those populations that are less susceptible to disease. Using southern oysters from Texas, Louisiana and Florida and strains from the Carolina's and the Delaware Bay they are placing oysters in floating trays at different sites in the Bay. The hope is to identify populations that are less susceptible to Dermo. If differences are found, then they may find a genetic marker to identify resistence.

As one scientist said, it has taken many years to deplete the Chesapeake Bay, it will take more than just a few years to replenish it.

"The New Oyster Wars" by Merrill Leffler. Maryland Marine Notes, Summer 1995. Maryland Sea Grant College, University of Maryland, College Park, MD 20742