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Research, Education, Outreach Summer 1995 SPOTLIGHT ON RESEARCH The New Oyster Wars: Can America Save Battling Disease in the Lab and Bay Its Fisheries? Many U. S. fisheries — from coast to coast and in the Great Lakes — are facing BY MERRILL LEFFLER historic lows. Will new gear restrictions, limited entry or n the final decades of the last other management tools be century, oyster wars in the able to turn the tide? Have Chesapeake pitted watermen our fisheries, a public trust I against the oyster police and resource, become another each other as they battled over the casualty of the “commons”? riches of the Bay’s “winter gold.” On September 11, 1995, No more. at the National Press Club in With those riches gone, oyster Washington, D.C., the national wars in the final decade of this network of Sea Grant pro- century are being fought below grams will sponsor a public water, not by watermen but by issues forum entitled, “Can poorly defended oysters and ma- America Save Its Fisheries?” rauding protozoans. Known as Panelists will include Michael Dermo (Perkinsus marinus) and Sissenwine, chief scientist for MSX (Haplosporidium nelsoni), these the National Marine Fisheries microscopic parasites have been Service; Bart Eaton, president battering oyster populations through- Probing the immune system of the oyster, of Trident Seafoods; Suzanne out the Chesapeake. One measure researchers witness a raging molecular Iudicello, vice president of the of this onslaught can be seen in battle between relentless parasites and the Center for Marine Conserva- commercial harvests — over these mollusc’s faltering defense mechanisms. tion; Billy Frank, chair of the last five years, harvests have fallen Northwest Indian Fisheries so low their landed value in Virginia, mistake. “This year,” he says, “we Commission; William Amaru, says Roger Mann of the Virginia have had the highest MSX infection a Northeast ground fisherman; Institute of Marine Science (VIMS), since 1959.” Wilma Anderson, executive “is less than the sale of one median Why are oysters so defenseless? director of the Texas Shrimp house in Hampton Roads.” Why aren’t they able to mount an Association; John Magnuson, So entrenched is Dermo on effective counterattack against Dermo University of Wisconsin; and bottom grounds in the Bay that even and MSX, as they have against other many others. in summers with good sets of new pathogens? Or conversely, why are For more information, call oyster larvae, the chances of oysters these protozoans so successful in Ben Sherman at Sea Grant’s surviving to harvest size by the eluding defenses the oyster immune national media relations office second or third year are at best slim, system throws at them? And can (301) 405-6381. at worst, nonexistent. According to anything be done to reverse the Eugene Burreson, a scientist at VIMS, devastation that these diseases have Dermo commands all of Virginia’s been wreaking? oyster bars except the upper James Until five years ago, there were few River. With all the emphasis on answers that evoked optimism, and no Dermo, people have tended to forget long-range plan for help. That is no MSX, says Burreson — that’s a (Continued on page 2) Oyster Wars, continued longer the case. In the last several years, says Roger Mann, “we have made quantum leaps in some areas of understanding.” One reason for these rapid advances has been a Congressionally funded program of research on oyster disease that has made consistent support possible on numbers of fronts, from molecular studies on the interaction between protozoans and the oyster immune system, to development of sophisti- cated techniques for monitoring the presence of Dermo and attempts at breeding strains of oysters that may eventually be able to resist the attacks of Dermo and MSX. The Cellular Front Once the Chesapeake’s most lucrative fishery, the oyster has fallen on hard times. Maryland’s 1994-95 harvest of some 162,000 bushels represents a fraction — about Scientists have long known that 14% — of the harvests of only a decade ago. hemocytes, cells in the oyster’s circu- lating fluid, play a major role in fending off invaders. Analogous to through a microscope. “You could go metals, chemicals — affect its growth the human body’s white blood cells, blind,” he says. “These new method- and behavior. though far less sophisticated, hemo- ologies give you a chance to count “Culturing the Dermo cell,” says cytes are the oyster’s first line of three million cells, not 300.” Chris Dungen, a research scientist at defense: in general, when a microbe Many of these studies depend on the Oxford Cooperative Lab, “was a invades, the hemocyte binds, then large amounts of Dermo. Thanks to breakthrough whose major benefits surrounds the attacker, and engulfs recent breakthroughs, scientists now we have yet to realize.” Two paths of it in a process called phagocytosis. have that advantage. The ability to investigation, one in Gerardo Vasta’s The cells release bursts of toxic com- grow Dermo in continuous culture in lab at COMB and another in pounds, specifically reactive oxygen the lab resulted from a near-simulta- Mohamed Faisal’s lab at VIMS, have intermediates (ROIs) such as hydrogen neous discovery two years ago by been revealing molecular armaments peroxide, says Robert Anderson of Mohamed Faisal and Jerome F. La by Dermo that are especially provoca- the University of Maryland’s Center Peyre at VIMS, Sharon Shrunk and tive, though the work is in early for Environmental and Estuarine Stephen Kleinschuster at Rutgers stages of investigation. Studies (CEES). When Anderson University, and Gerardo R. Vasta and Mohamed Faisal and Jerome La exposes these hemocytes to Dermo, Julie D. Gauthier at the University of Peyre are tracking enzymes that however, the hemocytes engulf the Maryland System’s Center of Marine Dermo releases when it attacks an parasite but he doesn’t see the ROIs. Biotechnology (COMB). oyster cell. Called proteases, these The question, of course, is why not? enzymes break down oyster tissue Dermo may survive for a number of and likely contribute to the oyster’s reasons, says Anderson. The parasite We have made quantum demise. The researchers found that may prevent oyster hemocytes from Dermo can grow and divide in triggering the ROIs, it may for some leaps in our understanding hemocytes of infected oysters, reason be able to withstand them, or suggesting, Faisal says, that “factors it may produce substances that are other than hemocytes may be impor- toxic to hemocyte cells. Before having that capability, it tant in resistance.” New molecular tools have been was difficult to obtain Dermo in pure While they have observed the making it possible for Anderson and form. Moreover, says Anderson, you presence of Dermo in the Pacific other scientists to better examine the could not get enough of it. “Now oyster (Crassostrea gigas), that oyster chemical weaponry that both oysters you can make it by the bucketful — appears more resistant than the and protozoans deploy. For example, it’s duck soup.” Growing Dermo in Eastern oyster (Crassostrea virginica). using molecular probes and chemilu- petri dishes makes it possible to Faisal is focusing on the possible minescent analysis to detect and study its life cycle and how different presence of special inhibitors in the quantify ROI production, Anderson environmental conditions — for Pacific oyster. If he can identify these, no longer depends on counting cells instance, salinity, temperature, heavy he could potentially develop “pro- 2 • MARYLAND MARINE NOTES tease blockers” that would act D E R M O M S X something like antibiotics in fighting the parasite. Perkinsus marinus Haplosporidium nelsoni Still another molecular battle may be taking place over iron. Iron is critical for growth, both to parasites like Dermo and host organisms like oysters. Because iron is generally much less available than other metabolic needs, competition for iron between the parasite and the host cell is intense, says Gerardo Vasta. Vertebrates have developed strategies against malaria, Vasta points out, by producing iron-binding proteins to reduce the levels of iron available to malarial parasites — “this slows the parasite’s growth rate and reduces the pathogenicity of the infection.” Recent studies in his lab, Sites of major MSX infestation he says, “indicate that Dermo has a Sites of major Dermo infestation Sites where MSX is reported, but strong requirement for soluble iron no major outbreaks and its growth rates are correlated with iron availability.” Environmental factors in the Often inadvertently spread from place to place, oyster diseases have plagued stocks of the Chesapeake may increase the avail- popular mollusc through this country and abroad, and have largely ravaged the famed ability of iron. For example, low Chesapeake oyster grounds. Maps reprinted courtesy of Susan Ford, Rutgers University. concentrations of oxygen — or its complete absence (anoxia) — occur in the Chesapeake Bay during summer months and trigger chemical reactions in the sediments that ity of oysters to Dermo. Fu-Lin Breeding for Disease Resistance release iron into the water. “This may Chu, also at VIMS, has done “The most important thing we’re help explain,” says Vasta, “why comparable studies with poly- doing that could make a difference in Dermo is more prevalent during the aromatic hydrocarbons (PAHs), the relatively near term is a cross summer months in oysters that are which, once released from the breeding program,” says Stan Allen of located in low dissolved oxygen combustion of fossil fuels, gather Rutgers University’s Haskins Shellfish estuaries like the Bay.” in Bay sediments. Laboratory on Delaware Bay. For Vasta speculates that “excessive The interrelated effects of some years, Hal Haskins and Sue iron accumulation in the oyster in multiple pollutants and the envi- Ford, also at Rutgers, have employed summer promotes proliferation of ronment remain a complex and traditional genetic breeding techniques Dermo, which may inhibit the oyster tangled web.

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