Scientists say a proposal by Maryland and Virginia officials to populate the Chesapeake Bay with the “Oregon strain” of Asian oysters faces a key problem: There aren’t enough of those oysters to do the job.
Only a handful of the so-called “Oregon strain” of the foreign Crassostrea ariakensis oysters are available to begin rearing the millions—if not billions—of oysters that would be needed to repopulate the Chesapeake, according to a report by the Bay Program’s Scientific and Technical Advisory Committee.
Oyster researchers say scores more would have to be brought from the oysters’ native habitats, most likely in China or Korea, to prevent inbreeding which could cripple efforts to build a self-sustaining population.
“There just flatly are not enough animals to do it with,” said Mark Luckenbach, a scientist with the Virginia Institute of Marine Science, who has been doing research on C. ariakensis. “I don’t think that was widely appreciated, especially by the management agencies.”
Stan Allen, the VIMS scientist who has been breeding C. ariakensis oysters for tests in the region, said all C. ariakensis brood stocks in the Bay stem from a “founder” population of fewer than 10 males and 10 females of the Oregon strain to breed. While that is adequate to produce oysters for research and the production of sterile oysters for aquaculture, he said more than 100 unrelated oysters should be used if a stocking program is begun.
“The bottom line is there isn’t enough genetic variability to do this responsibly,” Allen said.
Like humans, each oyster has its own unique set of genes which allows each individual to do some things better than other; some may reproduce better, while another may be superior at withstanding disease, and yet another adapts better to changing environmental conditions. Ideally, a population should contain as many of those genetic characteristics as possible.
“If you have a very limited genetic diversity, there is a tendency for the population to be less stable and more prone to unexpected events like disease or extreme climatic events,” said Christopher Langdon, a fisheries scientist at Oregon State University.
In addition, too few oysters increases the chances of inbreeding, which weakens the population. “We know from work with the Pacific oysters that if you inbreed them, their overall performance is reduced, so they tend to survive less and grow less,” Langdon said.
The shortage of oysters does not mean a stocking effort could not begin, scientists note, as long as there is a program to supplement the population with other C. ariakensis oysters.
But that means management agencies would have to do something they hoped to avoid—import oysters directly from Asia.
To minimize worries that the use of a foreign oyster could result in the accidental introduction of diseases, viruses or other unwanted organisms, the proposal from Maryland and Virginia specifically made the use of the “Oregon strain” of C. ariakensis their preferred alternative, because the oysters had been maintained in U.S hatcheries for decades, and are considered less likely to carry diseases or other pathogens than those imported directly from Asia.
Tom O’Connell, project management for C. ariakensis with the Maryland Department of Natural Resources, said concerns about limited genetic variability would be addressed this year during the development of an Environmental Impact Statement regarding a potential introduction. He said the Oregon strain was attractive because it has performed well in tests and would be available as a “starting point” for an introduction next year.
Any new oysters brought from Asia to support an introduction program would have to adhere to international protocols that call for at least two generations to be kept in quarantine before any animals are released into the wild.
“If you say you are going to use an Oregon strain, it is much less provocative than saying you are going to use Chinese oysters,” said Langdon, who works with C. ariakensis and other oyster species. “I think there are some major concerns that a geneticist would have if one used just the Oregon strain for restocking the Chesapeake. You need much greater genetic diversity.”
Langdon said it was a “great stretch” to refer to any C. ariakensis oysters as an Oregon strain. C. ariakensis arrived on the West Coast by accident in the 1970s while another species was being imported. But attempts to introduce oysters to West Coast waters were unsuccessful—no self-sustaining populations are known to exist in the wild in California, Oregon or Washington.
Only a handful of oysters were maintained by Langdon and others, and they are the “founders” from which almost all of the C. ariakensis oysters in the United States stem from. A few more have been brought from Asia in the past few years, but there are still too few to create the needed genetic diversity, scientists say.
Allen said it would be possible to begin an introduction into the Bay with oysters that are available now, but a plan needs to be put in place soon to supplement those with other oysters. He said it could take six to seven years to bring additional oysters from Asia, maintain them in quarantine for at least two generations, and then gear up to support a large stocking program in the Bay.
“You could certainly start the process,” he said, “but you wouldn’t want to rely on that as the sole source of material. That is my professional opinion on that subject.”