A team of scientists offered cautious support for rearing sterile Asian oysters in aquaculture in the Chesapeake, but warned against any effort to establish a wild population without years of additional research.
The much-anticipated report from the National Academy of Sciences also recommended against a “do nothing” option that placed all hopes on restoring the Bay’s native oyster. “Do nothing is not a good option, either for the industry, or the ecology,” said said James Anderson, chair of the Department of Environmental and Natural Resource Economics at the University of Rhode Island, who co-chaired the committee that wrote the report.
That could lead to a “rogue introduction” in which someone imported oysters directly from Asia and placed them in the water—along with any hitchhiking organisms that may be attached. By contrast, the aquaculture option could be more carefully controlled.
In that sense, the academy generally endorsed the approach being pursued in Virginia, which has approved the use of 1 million sterile Crassostrea ariakensis oysters in a large-scale aquaculture test beginning in September.
But it said the outright introduction which has recently been advocated by Maryland is “an imprudent course of action” given how little is known about the oyster and its potential impacts.
Interest in the foreign oyster is extremely high because tests in recent years showed that it grows fast in Bay conditions, resists diseases that have devastated native oyster populations, and has a taste that appears to make it highly marketable.
While interest has risen in C. ariakensis, populations of the already severely depleted native C. virginica sank even lower in recent droughts, which allowed diseases to thrive. This year’s harvest was an all-time low.
Besides being a marketable commodity, proponents see ariakensis as potentially filling the ecological niche once occupied by C. virginica by building reef habitats and filtering the Bay’s murky, algae-filled water.
Given all of the issues, state and federal agencies last year funded the academy, which is known for assembling teams of experts to analyze scientific issues, to review the potential of C. ariakensis—also known as the Suminoe oyster—in the Bay and make recommendations.
The 11-member team’s report offered a sobering assessment of the status—and future—of oysters in the Chesapeake. Neither C. ariakensis nor C. virginica is likely to populate the Bay in large numbers anytime soon, they concluded, repeatedly stating that there is no “quick fix” to the Bay’s oyster woes.
The report suggested the often touted benefits of oysters—providing habitat for other species and filtering water—while important, are likely overstated. And it’s unclear how much impact even a large population of oysters would have in today’s degraded Bay, which is beset with a host of other problems.
“The committee cautions decision makers and observers that it is unlikely that there exists any ‘quick fix,’ to the Chesapeake oyster situation,” Anderson said at a media briefing. “It is also unrealistic to expect that the oyster industry and the Chesapeake Bay water quality could every be fully returned to conditions found in the past.”
Although the committee generally endorsed long-term strategies being developed to restore the native species, it labeled the Chesapeake 2000 agreement’s commitment to achieve a tenfold increase in native oysters by 2010 as “naive.” Given the daunting problem of disease, significant increases in the native species may take decades, it said.
Aquaculture of sterile C. ariakensis is likely to have relatively high costs, which may limit production to the half-shell market which pays premium prices—something that would keep aquaculture at a relatively small scale in the Bay.
Even if reproducing oysters were introduced outright in the Chesapeake, it’s unclear that they would necessarily have a rapid rate of population growth. The spread of C. ariakensis would also be limited by some of the poor water quality conditions that affect the native species. About half of the historic oyster habitat in the Bay has been covered by increased sediment loads entering the Bay, preventing its use by either species.
The report cautioned that the Suminoe is no super oyster that can fend off all diseases. While it has not been affected by the oyster parasites MSX and Dermo, which have devastated the native oyster population, the report said that C. ariakensis should not be considered “disease resistant.”
There have been reports of large die-offs of C. ariakensis in China, and the oyster was deemed unsuitable for use in France because it is easily killed by a parasite that devastated the European flat oyster population. That parasite, Bonamia ostrea, is found as close to the Bay as Maine, although at low levels, the report said.
Understanding the threat posed by B. ostrea was one of the committee’s research recommendations.
Such issues underscore how little is known about C. ariakensis. Dennis Hedgecock, a committee co-chair and professor at the University of California’s Bodega Marine Laboratory at the University, said it would likely take five years of research before a better decision could be made about turning a breeding population loose in the Bay. “It is remarkable how little we know about ariakensis biology,” he said. The committee, in fact, said all options need more research.
Before any actions are taken beyond this year’s million-oyster test, federal and state agencies have agreed to a comprehensive environmental impact statement to explore the risks and benefits of using C. ariakensis in the Bay. Maryland officials have said they would hope that process could be completed in a year.
After the release of the report, Maryland Department of Natural Resources Secretary C. Ronald Franks said he would like to stick with an “aggressive time line” and insisted that key answers could be achieved rapidly. “When you look at the serious condition that exists in the oyster industry, it’s an acute problem,” Franks said.
Bolstering oyster stocks with nonnative species is nothing new, the committee pointed out. Globally, almost 99 percent of the oyster harvest consists of the Pacific oyster, C. gigas, which has been introduced in France, the West Coast, Australia and elsewhere to boost production.
Yet introductions using a relatively well-known species have had a wide range of results, which points to the difficulty in predicting what would happen in the Chesapeake with a poorly studied oyster.
France successfully introduced C. gigas to replace native oysters that were devastated by disease, causing a collapse in the oyster industry. Beginning in 1971, hundreds of tons of C. gigas were released into sanctuaries. Aided by successful reproduction, the populations quickly expanded into surrounding areas and by 1975 it was supporting a harvest. The fishery is now self-sustaining.
But extensive efforts to introduce reproducing stocks of C. gigas into the West Coast failed, and the accidental introductions of several harmful, nonnative species were a result of those attempts. Today’s West Coast oyster fishery is maintained through hatchery production and the oyster industry has switched largely to aquaculture.
By contrast, when C. gigas was brought to New Zealand and Australia, it unexpectedly outcompeted the commercially valuable native species, sharply reducing its harvest.
Numerous efforts in past decades have tried to stock C. gigas in the East Coast and in the Bay. None succeeded, although one of the failed efforts resulted in introducing the deadly oyster disease MSX to the region, which has since plagued the native oysters.
“Our committee’s study revealed that despite the positive results of some oyster introductions, some extremely negative consequences have been observed as well,” Anderson said.
C. ariakensis is even more difficult to predict. The committee repeatedly commented on how little information was available about the oyster. Much of what is known comes from laboratory tests which may not replicate real-world conditions.
The oyster, a native of China, does grow successfully in Japan. It was inadvertently introduced to Oregon in the 1970s with shipments of other oyster spat from Japan, but conditions apparently were not favorable. No known wild populations exist on the West Coast today, although some stocks are retained at hatcheries.
On the surface, the report said C. ariakensis appears to be “well suited” for the Chesapeake. It seems to live in roughly the same conditions as the native species. If introduced, preliminary studies suggest it is “very likely” to become established wherever C. virginica was historically found. The two oysters would likely overlap in range and consume similar food, but it’s unknown how they would compete in the wild.
Limited laboratory studies suggest larval C. virginica would outcompete larval C. ariakensis for space. But if there is competition, the species that spawns first would likely have an advantage, the report said, and it’s not clear which would be the first spawner.
If it became established in the Bay, the Suminoe oyster would likely provide similar ecosystem functions, such as water filtering, as the native species, but its impact on the Bay would depend on the density of oysters. The report said it would likely take “decades” to build a population that would resemble C. virginica before its decline—the time frame would depend on how well C. ariakensis adapts to the Bay’s environmental conditions and how long it takes wild populations to establish themselves.
At the media briefing, scientists said stocking C. ariakensis in the Bay would require a larger effort than the successful stocking of C. gigas in France, which is the largest introduction effort to date and took nearly a decade to complete.
A major unknown is whether C. ariakensis builds reefs like the native oyster. Reports suggest it does occupy reefs in its native habitat, but the committee said that it’s unclear whether the reefs were actually formed by C. ariakensis. If it does not build vertical reefs in the Bay and instead grows horizontally over the bottom, it could crowd out native bivalves, some of which are important food for blue crabs. On the other hand, if it behaves like C. virginica, it is unlikely to compete with the native bivalves.
At the extreme, the report cautioned that many characteristics that make C. ariakensis attractive—tolerance to a wide range of environmental conditions, rapid growth and high reproductive capacity—“are the same characteristics that have been attributed to aquatic nuisance species.”
If the population expanded rapidly and could not be held in check by natural predators and fishing, it could become a major fouling species like the zebra mussel in the Great Lakes, clogging water intake pipes, attaching to the hulls of ships, and displacing native species, including C. virginica. Such an event could alter the entire food web, causing a shift in Bay productivity from the surface to the bottom, a change that would favor bottom feeders such as sheepshead and bluefish over striped bass and menhaden.
If a reproducing population becomes established in the Chesapeake, the report said it is “highly likely” they will disperse to other areas. Because such an introduction is irreversible, and its potential impacts so hard to predict, the report called it an “imprudent” action at this time.
The committee recommended using sterile oysters in aquaculture because it allows some relief to the beleaguered oyster industry, while providing some time to learn more about the foreign species.
Hatchery-produced oysters for aquaculture present minimal risks of accidentally introducing diseases or unwanted species into the Bay. And the use of “triploid” oysters—ones bred to have three sets of chromosomes instead of two—has only a minimal risk of reproduction. The technique for rearing triploids being used in Virginia appears to be about 99.9 percent effective.
There is a chance that a small number of triploid oysters would revert to normal, two-chromosome “diploids” over time, but it would likely take three to four years for that to happen, and even then it’s unclear whether they could actually reproduce, the report said. Aquaculture practices that keep oysters contained—rather than placing triploids on the bottom for later harvest—would decrease the chance of oysters being in the water long enough to revert to diploids.
But the report acknowledged that aquaculture with triploids benefits Virginia more than Maryland. Watermen in Virginia have more experience with aquaculture, and the state’s long history of leasing bottom grounds for production provides in-water areas that can be used for aquaculture production.
Triploid aquaculture has its drawbacks. The cost of producing triploids and the need for “biosecurity” measures to track oysters and make sure they are not released into the water would add to production costs. The report expressed doubt that aquaculture could economically produce oysters for oyster packing houses around the Bay, which now import oysters to meet their needs.
“Watermen using these methods will want to make sure that they get the best return on their investment, and this return is more likely to be found in the half-shell rather than the shucked market,” the report said. That would reduce demand for triploid oysters, which, in turn, would likely reduce ecological benefits from the program as fewer oysters would be grown.
That is still a better option than doing nothing, the scientists said, as efforts to restore the native species are unlikely to produce any benefits soon. That would cause “irreversible” effects on watermen and their communities.
It’s likely that a comprehensive oyster management plan could achieve results over a period of time, especially if aided by the development and use of disease-resistant strains of C. virginica. But the report said the Bay Program’s Chesapeake 2000 agreement goal of achieving a tenfold increase in oysters by 2010—a project expected to cost at least $100 million—is overly optimistic.
“It will take decades and possibly centuries to restore native oyster populations and oyster reefs,” the report said. “The time frames presented in the Chesapeake 2000 agreement appear ambitious and probably naive.”
Relying on native oysters increases the likelihood that frustration would grow to the point where someone would attempt a “rogue introduction” of C. ariakensis, which the report identified as one of the greatest risks to the Bay. Such an introduction carries a large risk that parasites and other organisms would “hitchhike” along with the oysters and pose threats to native Bay species.
The report said a rogue introduction using C. ariakensis would be remarkably easy. It said public education was needed to warn people against such actions, and to increase public vigilance.
The report also raised the question about who—if anyone—has the responsibility to regulate the introduction of a foreign species. Although state and federal agencies have agreed to cooperate on the development of an environmental impact statement, it’s unclear that federal agencies can regulate introductions made by states.
It said binding regulations to govern introductions are needed, and suggested that the Bay Program should be given such authority. The committee praised the Bay Program’s handling of the issue, as well as its 1993 policy on nonnative introductions which created a framework for multiple jurisdictions to discuss the C. ariakensis issue, although recommendations are nonbinding.
“The committee feels that the process used so far is a model for elsewhere in the United States,” Anderson said.