e t w o r k news 



North Carolina Sea Grant is part of One of the first steps in under- 

 a network of Sea Grant programs that standing Dermo came in the ability to 

 rim our nation along the Great Lakes culture the disease in the laboratory. 

 and ocean coastlines. There are 29 Researchers from the Virginia Insti- 



programs, reaching from Hawaii to tute of Marine Science (VIMS). 



Puerto Rico, from Alaska to Florida. Rutgers University in New Jersey and 

 Each sponsors an innovative 

 array of research projects, 

 education and outreach 

 activities. 



Beginning with this 

 issue, Coastwatch will peri- 

 odically update you on the 

 research results, extension 

 projects and publications 

 produced by the Sea Grant 

 network. We hope you '11 

 develop a better understand- 

 ing of Sea Grant and its 

 nationwide efforts to pro- 

 mote the wise use and stew- t^^^mBB^KBEflf 

 ardship of our ocean and WSE&F^ 

 Great Lakes resources. 



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Battling Oyster 

 Diseases 



Two microscopic 

 parasites, known as Dermo 

 (Perkinsus marinus) and 

 MSX (Haplosporiduium 

 nelsoni), have taken their 

 toll on oyster populations on 

 the East Coast. The diseases 

 have ravaged the famed 

 Chesapeake Bay oyster 

 grounds, and they've had 

 devastating effects in North 

 Carolina too Growing oysters at the surface helps avoid diseases. 



To better understand 



the parasites and their killing effects on the University of Maryland Center of 



oysters, a battalion of Sea Grant re- Marine Biotechnology (COMB) 



searchers is studying the diseases, the developed techniques for continuous 



environmental factors that favor the culture that make it possible to study 



parasites' spread, the oyster's lack of the parasite's life cycle and how 



natural defense and possible ways to different environmental factors — 



control or eliminate the diseases. This salinity, temperature, heavy metals, 



research is part of the Oyster Disease chemicals — affect its growth and 



Research Program funded by Congress behavior. 



as a special initiative of the National Sea VIMS scientists are tracking the 



Grant College Program five years ago. enzymes that Dermo releases when it 



attacks an oyster cell. Called proteases, 

 these enzymes break down oyster 

 tissues and likely contribute to the 

 oyster's death. The researchers found 

 that Dermo can grow and divide in an 

 oyster's hemocytes, cells in the 



mollusk's circulatory system 

 that fend off invading dis- 

 eases and bacteria. Since the 

 hemocytes don't ward off the 

 Dermo, other factors may be 

 important in resistance. 



In particular, the Pacific 

 oyster {Crassostrea gigas) 

 has been found to be more 

 resistant to Dermo than the 

 Eastern oyster {Crassostrea 

 virginica). This resistance 

 may be linked to special 

 inhibitors in the Pacific 

 species. If identified, pro- 

 tease blockers could be 

 developed that would behave 

 like antibiotics in fighting the 

 parasite. 



At COMB, scientists are 

 studying how the availability 

 of iron affects Dermo' s 

 presence and growth. Recent 

 studies indicate that Dermo 

 has a strong need for soluble 

 iron, and its growth rates are 

 correlated with iron availabil- 

 ity. 



Environmental factors in 

 Chesapeake Bay and North 

 Carolina estuaries may 

 increase the availability of 

 iron. Low concentrations of 

 oxygen, called hypoxia, occur in both 

 areas in the summer and trigger chemi- 

 cal reactions in the sediment that 

 release iron into the water. This may 

 explain why Dermo is more prevalent 

 in summer months in oysters located in 

 estuarine waters with low dissolved 

 oxygen. 



Scientists speculate that excessive 

 iron accumulation in the oyster in 

 summer promotes the proliferation of 



22 NOVEMBER/DECEMBER 1995 



