Interest in bolstering the Bay’s flagging oyster harvests by using a nonnative species is accelerating among watermen in both Virginia and Maryland, greatly increasing the likelihood that a foreign oyster will ultimately be introduced into the Chesapeake.
Whether that is good or bad, no one can say for certain.
But a recent symposium on the issue that brought together scientists, policy makers and watermen from both states suggested that the time has come to begin evaluating what could happen if a nonnative oyster population takes hold and begins expanding in the Bay.
Until now, research has been largely confined to the notion that hatchery-reared, reproductively sterile oysters — known as triploids because they have three sets of chromosomes — might be used in aquaculture to produce the foreign oysters. Theoretically, that would prevent a reproducing population from being established in the Chesapeake.
But symposium participants concluded that process was not fail-safe. Ultimately, they said some oysters would revert to “diploids” having the normal set of two chromosomes. In that case, they might spawn, launching a self-sustaining population in the Bay and, ultimately, the East Coast.
Participants were divided whether that would be helpful or harmful to the Bay, but most agreed that the time had come to start answering that question.
“A lot of the research questions we need to address now are going to be related to diploids,” said Gene Burreson, director of research for the Virginia Institute of Marine Science, which hosted the symposium. “I think the research focus is going to shift.”
At the center of the issue is the future of Crassostrea ariakensis, an oyster native to Southeast Asia. Research has shown that it not only thrives in the Bay — growing much faster than the native Crassostrea virginica — it also appears resistant to the diseases that have devastated the native species.
Further, taste tests have shown that most people can’t tell the difference between ariakensis and virginica, raising the possibility that it could become a unique Chesapeake Bay product in the marketplace.
‡or the past two years, the Virginia Seafood Council has secured permits from the Virginia Marine Resources Commission to grow sterile ariakensis oysters in controlled aquaculture projects in different parts of the Bay. Last year, 6,000 oysters were grown and used in market studies; this year 60,000 were put in the water.
Although no formal request has been made, it’s widely expected that the council next year will seek 1 million triploid ariakensis oysters — the maximum number that can be produced at VIMS. “It is only a matter of time before we get another request for triploids,” said Jack Travelstead, the VMRC fisheries chief.
But 1 million oysters is only a fraction of market demand for 270 million oysters that industry officials say exists in the state. They would like to see production ramped up to that number within five years by using private hatcheries to rear more tripl˜id oysters. “I’d like to see the triploids move forward immediately,” said Tommy Kellum, of Kellum Seafood, an industry representative on the council.
In addition to aquaculture, industry and watermen representatives at the symposium said they would like to see an outright introduction of diploid ariakensis oysters in the Chesapeake beginning in 2003. That would jump-start the creation of a reproducing nonnative population that could eventually be harvested in the wild.
With oyster harvests almost nonexistent in Virginia, interest in ariakensis is so high that five counties have already passed resolutions calling on the state to begin stocking diploids in the wild.
That has raised concern among many scientists who worry that such an introduction could bring unpredictable consequences for the Bay, possibly introducing a new virus into the Chesapeake, or competing with the native oyster for available habitat.
Because of such concerns, Maryland officials have staunchly opposed any use of ariakensis — even triploids — in the wild.
“Whether it’s a triploid or diploid, the state is opposed at this point to an introduction of a nonnative species into the open waters of the Bay,” said Carolyn Watson, assistant secretary of the Maryland Department of Natural Resources. “There is a risk element, and we don’t want to take that risk with the Chesapeake Bay.”
But several Maryland scientists at the symposium suggested the time had come for the state to begin experiments with the foreign oyster.
½nd, Larry Simns, president of the Maryland Watermen’s Association — which in the past opposed the use of other foreign oyster species — agreed that Maryland should begin its own research.
“I’m very supportive of doing some research on it to see if there would be any positive or negative effects,” Simns said. “If Virginia goes ahead without us, we could be left behind.”
Like watermen in Virginia, Simns said if the oyster is used in the Bay, it should include the stocking of a reproductive population and not be limited to triploid oysters reared in aquaculture.
If it’s restricted to aquaculture, he said, “it means no one but some big private company is going to take over the whole thing” — leaving many watermen no better off than they are today.
As recently as the the late 1970s, oysters were the Chesapeake’s most valuable commercial fishery, with Baywide harvests of about 7 million bushels annually. But the arrival of two diseases — MSX and dermo — devastated the oyster population, killing the vast majority before they can reach market size. Oyster harvests have been almost nonexistent in Virginia over the past decade, and have ranged between 200,000 and 400,000 bushels in Maryland in recent years.
Maryland is slightly better off because its portion of the Bay is periodically flushed with low salinity water, which reduces the virulence of both diseases. As a result, officials believe they can craft a program that would rebuild the native oyster population over time. In Virginia’s high salinity water, the diseases are always present, and officials there believe it could take decades for native oysters to build enough disease tolerance to substantially rebuild the population.
In 1994, the Virginia General Assembly ordered VIMS to research the possibility of using nonnative oysters in the Bay, both in aquaculture, and for a possible introduction of a self-sustaining population.
Initial work with Crassostrea gigas, an oyster widely used in aquaculture around the world, yielded disappointing results. But work in recent years found that ariakensis — an oyster not widely used elsewhere — seemed to thrive in the Bay.
The focus of the VIMS research has been on finding ways of mass-producing triploid oysters that could be grown without launching a reproducing population in the wild.
The process that produces triploid oysters is not 100 percent effective, though, and over time some of the oysters begin to revert to diploids, which may have the possibility of reproducing, although that has not been observed so far in laboratory tests.
While risks can be minimized, scientists at the symposium concluded that over time, the widespread use of triploids would almost certainly lead to diploid ariakensis oysters in the Bay.
In large part, that is because catastrophic events such as hurricanes — and even less powerful storms — would scatter oysters from aquaculture facilities. As they could not be gathered for harvest, those oysters would have more time to revert to diploids. It’s also possible that such storms would flood hatchery operations, potentially freeing breeding stocks that are used to rear triploid oysters.
“Over the long term, we’re talking about diploids in the water,” Burreson said. “But we don’t know what that long term is. I don’t think it’s the next decade.”
A more imminent likelihood — and a bigger risk for the Bay — is that someone could take the matter into their own hands and bring a reproducing stock of ariakensis to the Chesapeake and illegally release them with hopes of starting a population.
Although native to Southeast Asia, the oysters can be obtained from hatcheries on the West Coast. Further, North Carolina plans to begin research with the species.
Such a renegade introduction was considered highly likely at the symposium. It was also considered to pose the greatest threat to the Bay because oysters brought directly to the Chesapeake from somewhere else could bring along other diseases and pathogens as hitchhikers.
In fact, scientists now believe that the disease MSX reached the East Coast through a failed attempt to introduce gigas in the region during the 1940s or 1950s.
÷It’s quite easy to introduce, and yes, you could have a lot of problems with it,” said Roger Newell, an oyster expert with the University of Maryland’s Center for Environmental Science. “There is also a high probability that someone will do it.”
Newell, who led the discussion among scientists at the symposium, said he supported the use of triploids in aquaculture because the risk of introduction could be better managed.
But the risks from a renegade introduction were profound, he said. It’s possible the foreign oysters would not survive in the wild, but they would carry diseases that might further afflict native oysters — in effect creating a “lose-lose” scenario for oysters, he said.
By contrast, oysters reared in laboratories are inspected for disease, and only the offspring of oysters brought from other locations are used for studies, minimizing the potential of disease introduction.
Even that is not a sure thing: Scientists acknowledge that while they can find parasites and pathogens, it is difficult to be certain that all viruses in foreign oysters could be detected.
With a likelihood that reproducing ariakensis could end up in the Bay, many symposium participants suggested stepped-up research to determine the potential risks and benefits of having a reproducing ariakensis population in the Chesapeake.
The foreign oyster could help clean up the Bay, by restoring the water-filtering capacity that was lost as the native oyster population plummeted. Newell has calculated that the Bay’s oyster population once filtered all of the water in the Chesapeake in a matter of days, while it takes today’s population about a year to do the same job.
Historically, it is thought that oysters were the most ecologically important species in the Bay. More oysters — even if they are nonnative — would restore that lost filtering capacity, not only reducing algae blooms, but also controlling undesirable species such as jellyfish, which have thrived as oysters declined.
By providing an alternate species for watermen, ariakensis could reduce fishing pressure on native oysters, possibly helping their stocks to recover. In addition, field studies suggest that ariakensis may provide a solid substrate on which virginica larvae could settle, thereby providing more oyster habitat.
At the least, shells from ariakensis aquaculture projects could be used to build reefs for native oysters: Restoration efforts increasingly face a shortage of oyster shells when constructing reef habitats.
On the other hand, the oysters do carry some serious risks, such as bringing undetected viruses.
There are also concerns that ariakensis may not build extensive reefs like virginica, which can provide important habitat for other species. Most of those reefs are now absent from the Bay as the result of harvest and disease.
If ariakensis and virginica oysters spawn at the same time in the wild, their sperm could fertilize each others’ eggs producing a hybrid that would die in its larval stage, never being able to reproduce. That could fill the Bay with unreproductive “duds” — as one symposium participant put it — and threaten the survival of both species.
“It’s difficult to figure out what level of coexistence we might have,” said Stan Allen, the VIMS scientist who has been leading much of the ariakensis work. “But it’s likely the two species will coexist.”
Another concern is that new emphasis on ariakensis could detract from efforts to restore the native oyster at a time when funding is already “pretty lean,” said Rob Brumbaugh, of the Chesapeake Bay Foundation, which has opposed the introduction of diploids in the past, but not taken a position on the use of triploids. “We would be diverting resources from restoration just to foster triploid aquaculture,” he said.
Many scientists at the symposium tended to oppose an outright introduction of diploids — at least until some of the key questions are answered.
For example, many scientists generally believe that ariakensis could spawn in the Bay, although no one is certain, and their exact spawning conditions are unknown. It would take more research to determine whether a reproducing population could actually survive in the Chesapeake — efforts to introduce gigas decades ago failed.
Even if they survive, many contend that the watermen’s hopes of establishing a harvestable population with reproducing ariakensis oysters in the Bay were highly optimistic: Most said it would take decades for a wild population to reach a harvestable size. “It’s a long-term process,” Burreson said.
But, Burreson said, if watermen and industry representatives are satisfied with using triploid oysters for several years, it would give researchers time to begin answering some of the questions surrounding ariakensis in the Bay.
“We can go a long way toward reducing some of the uncertainties,” Burreson said. “But we can never predict the ultimate consequences. It’s too complex of a system.”