Researchers at Rutgers University, University of Maryland, University of Delaware and the Virginia Institute of Marine Science are working to breed a better oyster that is more likely to survive diseases in the Bay’s water.
Cross-breeding native oysters at research institutions throughout the mid-Atlantic region has produced an oyster that is resistant to MSX and more tolerant of Dermo. Dubbed “CROSBreed,” this oyster is currently being produced in hatcheries and will be planted on reefs this fall.
In addition, efforts are under way to selectively breed older, larger and presumably disease-tolerant oysters collected from areas throughout the Bay. Altogether, researchers say that as many as a dozen strains with different disease-resistant traits are currently being bred.
In fact, Stan Allen, Director of the Aquaculture Genetics and Breeding Technology Center at VIMS, envisions that someday a catalog will allow aquaculturists and oyster gardeners to choose oyster varieties best suited for their local water conditions. Aquaculturists need oysters that will survive to harvestable size, so disease-tolerant varieties that can reliably survive two to three years would substantially boost the struggling industry.
Selectively bred, disease-tolerant oysters may help produce stronger stocks for restoration, but their long-term potential for that purpose remains unknown. Hatchery-reared, disease-tolerant oysters are reproducing under natural conditions, but in nature they spawn with wild oysters, immediately diluting their selective breeding. The monitoring of how well selectively bred oysters survive, reproduce and pass on their disease-tolerance is just beginning.
A recommendation from Virginia’s Holton Plan, a blue ribbon panel report compiled in 1991 by an advisory group of stakeholders, directs VIMS to explore the feasibility of introducing non-native oyster species to the Chesapeake Bay.
VIMS recently completed a field study comparing Crassostrea virginica, the Bay’s native species, to Crassostrea gigas, a Pacific Ocean native. Results showed Crassostrea gigas survived disease better and grew faster than the Bay’s native oyster in high salinities typical of the Atlantic Coast along Virginia’s Eastern Shore. The native oyster outperformed the Pacific oyster in low salinities.
Tom Gallivan, a marine scientist with the Aquaculture Genetics and Breeding Technology Center and Virginia Sea Grant at VIMS, notes that raw Crassostrea gigas has a very poor flavor when compared with Crassostrea ariakensis, a disease-resistant species from the southern China region. C. ariakensis is in the early stages of study.
Because the introduction of non-native species can have wide-ranging and unpredictable consequences to ecosystems, researchers work with triploid non-native oysters under controlled conditions. Triploid oysters do not produce viable offspring.
Non-native species might be useful as sterilized aquaculture oysters, bred in hatcheries and raised under controlled conditions exclusively for harvest. As genetic research progresses, the possibility of transferring disease-resistant genes to native oysters also exists. At this time, the exploration of non-native species remains small-scale and tightly controlled.