Contents

Crisis and Controversy

A Timeline For More Information

What's Killing the
Native Oyster?

Summary of a Field Trial

The Hatchery Connection

Conferences Publications Web Resources

Oyster Research and Restoration Meeting

By Merrill Leffler

The inability so far to restore sustainable native oyster populations or to successfully cultivate them has left watermen and processors calling for, if not demanding, introduction of a non-native species - the Suminoe or Chinese oyster Crassostrea ariakensis - that
they believe will survive.

Years of parasitic disease have left Chesapeake Bay oysters and the industry that has depended on them a faint shadow of what they once were. In 1982, the Maryland Department of Natural Resources (DNR) issued nearly 5300 licenses to watermen who had been hauling an average of 2.5 million bushels of oysters a year from public grounds. The speculation is that harvesters this year may be lucky to bring in 50,000 bushels. Virginia watermen have been considerably worse off. Before MSX disease began killing oysters in the lower Bay in the late 1950s and Dermo in the 1980s, Virginia's private leaseholds and public grounds had yielded more than four million bushels - in 2000 and 2001, the yield has sunk to 20,000.

Many in the Bay industry feel that Crassostrea virginica, the Bay's native oyster species, is on the verge of failure, at least as far as the traditional oyster fishery goes. "This could be the year that we declare the economic extinction of the Chesapeake Bay oyster fishery," says Pete Jensen, former head of Fisheries for Maryland DNR. It is because of the inability so far to restore sustainable oyster populations or to successfully cultivate them that watermen and processors are calling for, if not demanding, introduction of a non-native species - the Suminoe or Chinese oyster Crassostrea ariakensis - that they believe will survive. Given the state of the native oyster, the question of whether or not - let alone how - to introduce a new species to the Chesapeake is one that poses complex challenges that have ecological and social implications.

The Crisis:
Desperate Efforts to Restore the Native Oyster

Reef Building

Millions of dollars are being spent to try to restore reproducing populations of native Bay oysters. "Reproducing" is the operative word. In Maryland so far, disease-free oyster seed (called spat) planted in low salinity locations often will contend with disease and eventually reach harvestable size, says Kennedy Paynter of the University of Maryland College Park. However, he is quick to add, oysters in these regions sometimes grow slower and recruitment of young oysters, or spatfall is infrequent. Historically, Virginia's high salinity waters provided richer conditions for oyster spawning - in the James River, the Great Wicomico and elsewhere. Seed oysters from these rivers provided state growers with spat that they could purchase and plant on their leased grounds. Those once abundant seed grounds have largely fallen victim to MSX and Dermo.

The Chesapeake Bay Program is committed to a tenfold increase in oysters by 2010 (over the base year of 1994) as part of the Chesapeake 2000 agreement, a broad range of targeted goals that state and federal officials have officially signed on for. The signatories include the governors of Maryland, Virginia and Pennsylvania; the Mayor of the District of Columbia; the head of the U.S. Environmental Protection Agency; and the Chesapeake Bay Commission, a tri-state legislative body. The commitment to restoring oyster populations gives focus and a deadline to efforts that were already underway in Maryland and Virginia, particularly to help rehabilitate their fisheries.

A decade ago, the Virginia Marine Resources Commission (VMRC) began large-scale construction of oyster reefs in the mainstem Bay and its tributaries. Once a structural feature of the Chesapeake, oyster reefs were virtually leveled over the nineteenth and twentieth centuries by harvesting techniques; they were then silted over by runoff and the remaining oyster populations have been battered by disease. Based on historical records and scientific studies, it was reasoned that broodstock planted on reconstructed three-dimensional reefs would help oysters once more produce sustainable populations.

Like other Crassostrea species, C. virginica reproduces by "broadcasting," or releasing, millions of eggs and sperm directly into the water; the fertilized eggs then become free-swimming larvae. Large reefs, with spawning oysters in close proximity to each other, would increase the probability of many more larval oysters. It is those larvae that after two or three weeks of feeding and swimming search for a hard surface - preferably other oyster shells - on which to cement themselves.

The Virginia Oyster Heritage Program is a more recent initiative that, under the direction of VMRC's Jim Wesson, has been building three-dimensional reefs (six- to eight-feet tall) with the concept that they would serve as breeder reefs: stocked with broodstock, larvae might set on the reef or in surrounding 25-acre area of deep layers of shell.

Maryland Department of Natural Resources (DNR), too, undertook new approaches for promoting oyster recovery by developing sanctuary sites and managed harvest reserves. Sanctuaries, which are off-limits to harvesting, were developed with the idea that they would function as breeder reefs, some of which have been planted with disease-free oyster seed (see "Don Meritt: The Hatchery Connection") and others with natural seed that DNR moves from public grounds that historically have gotten good "strikes" of spat.

"Most of those native oysters will die before they reach market size. . . . It's worse than playing the stock market when you put oysters in the Bay."

The reserves, by agreement among DNR, the Maryland Watermen's Association (MWA) and the Oyster Recovery Partnership (ORP), a non-profit organization that develops and implements restoration projects, are closed to harvest until oysters reach four inches (Maryland's legal minimum is three inches). The reserves are to be monitored regularly - if disease is found to be impacting under-four-inch oysters, the reserves will be opened to immediate harvest. If the oysters reach four inches, then "a predetermined percentage of harvested oysters will be allowed before each site is again closed," says Charles Frentz, ORP director. Managing for sustainability is a new idea in Maryland - whether or not it will work depends on getting oysters to survive.

The sanctuaries and reserves are well and good, says waterman Larry Simns, president of the MWA, "but most of those oysters will die before they reach market size. . . . It's worse than playing the stock market when you put oysters in the Bay." Again, this has been especially so in Virginia where Jim Wesson has overseen the construction of 50 reefs that have held so much promise. "We get high spat set on the reefs," says Wesson, "but the oysters just don't survive to become marketable adults." There are oysters that do survive, of course, animals that have an inherent genetic make-up that enables their immune system to fight the withering effects of MSX or Dermo.

Over enough generations, survivors of each spawn might theoretically rebuild their own populations naturally. How many generations would that take? Twenty-five? Fifty? One hundred? For those in the industry, it is not soon enough. The same goes for those who are working to restore oysters for their ecological value. In the meantime, the reefs themselves could collapse because oysters are not surviving and building shell faster than they are falling apart from erosion, sedimentation and other physical processes, and from predators such as boring sponges and oyster drills.

"What we're trying to restore is ecological and economic function," says Wesson. "That goal of a tenfold increase in Bay oysters is a just descriptor. What we're really trying to get back is a tenfold increase in services that oysters provide - in filtration, in habitat reconstruction and in harvest. The only way we can get that," he says, "is with an adult oyster that survives." With an estimated cost of $350,000 for each one-acre reef and 25 acres of surrounding shell, and with oysters not surviving to harvest size, it is no wonder that he and others have become so discouraged.

Managing around Disease

When it comes to Chesapeake Bay oysters, one waterman says, disease is in the driver's seat.

More than a decade ago, the recognition that disease was the overriding issue in the Chesapeake, and potentially in other coastal waters, led to Congressional legislation that established the Oyster Disease Research Program (ODRP). Its major goal has been to develop research-based approaches for restoring the commercial and ecological viability of oysters that have been decimated by disease, says James McVey, who is with NOAA's National Sea Grant Program, which administers the program.

ODRP has underwritten a number of scientific and technological advances that are now being employed by state agencies and commercial operations. Among them are molecular tools for rapid diagnosis of Dermo infections, which are caused by the protozoan Perkinsus marinus. With our new technologies, we can detect just one cell of Perkinsus, says Gerardo Vasta of the Center of Marine Biotechnology, part of the University of Maryland Biotechnology Institute. Such tools as these, which are currently being field tested, can help aquaculturists and resource managers monitor oyster populations regularly and, if Dermo infections are found to be increasing, that may be a signal for precautionary measures such as growers moving cultured oysters to lower salinity waters or managers developing plans for harvests of reserves before disease becomes endemic.

ODRP has assisted researchers in designing predictive models to manage around disease and particularly in furthering the development of hatchery-bred strains of disease-resistant oysters. "We've had pretty decent results with breeding oysters resistant to Dermo and to MSX," says Standish Allen of the Virginia Institute of Marine Science (VIMS), "though getting resistance to both is the trick." Allen is a geneticist who has been leading the development of strains known to scientists as CROSBreeds and DEBYs, two of several that are being tested in Chesapeake and Delaware bays. With ODRP support, Allen has been working with researchers in Maryland, Delaware and New Jersey on field studies to compare these strains with local oysters and those from elsewhere on the east coast, particularly from Gulf coast waters in Louisiana where Dermo has been present since at least the 1940s.

"Our original intent was to develop superior strains of oysters for aquaculture," says Allen, "but there is a different intent now, which is to use them for restoration." Is it appropriate, he asks? Can they be used for the ecological "services," such as filtering and habitat construction and for enhancing the fishery as well? "In Virginia, there's not much of a choice," he says. "If we use wild stocks, we simply will not get survival. So we are doing both."

CROSSBreed and DEBYs are being planted on reefs, though not yet in large numbers. What is the appropriate planting density on a reef? How many reefs are necessary in a particular river system? What dimensions? Where should they be located? With all that is known about oysters, there is so much we don't know, says Kennedy Paynter.

A strong advocate of reef reconstruction, Paynter has been working with the Oyster Recovery Partnership and the Maryland DNR on sanctuary reefs in the Patuxent, the Choptank and the Chester rivers and is carrying on long-term comparative studies of reefs planted with disease-free spat from the hatchery and spat that have been moved from public grounds. He is trying to develop sophisticated measures of the ecological value of reefs and has been studying oyster longevity in relation to disease and reef structures. He has found, for example, that the mean time to infection with hatchery seed planted on clean bottom may be several years, while for seed planted on top of infected oysters it could be months. The problem, though, is that while oysters may survive for more than four years in low salinity (under 12 ppt salt), spat settlement is typically infrequent. The salinities are at the low end of the oyster's spawning range. On the other hand, if salinities rise significantly, they are then subject to disease.

"Unfortunately, we've learned that we don't have a way to design restoration strategies to get around MSX," Paynter says. "The oysters we put in low salinity waters will be long-lived, create substantial habitat and filter significant amounts of water." However, though these oysters provide "ecological service," researchers don't know if they will contribute to annual recruitment and enhance sustainability of the population overall.

Non-native Oysters
in the Chesapeake

1949
Oyster disease Dermo found in Chesapeake Bay

1959
Oyster disease MSX devastates populations in Virginia portion of Chesapeake Bay

1985
Dermo disease causes steep declines in oyster populations in Maryland portion of Bay

1991
Virginia aquaculture industry requests introduction of non-native oysters

1993
Chesapeake Bay oyster harvest reaches historic low; Chesapeake Bay Program (CBP) adopts non-native oyster policy (Crassostrea gigas and C. ariakensis); VIMS conducts first field tests of disease tolerance in C. gigas

1995
VA legislature mandates VIMS to develop a strategic plan for shellfish research

1996
CBP forms ad-hoc panel to guide research on C. gigas and C. ariakensis

1997
CBP's Living Resources Subcommittee (LRSC) accepts ad-hoc panel's recommendations

1999
VIMS publishes research showing low commercial potential for C. gigas; Virginia Marine Resources Commission (VMRC) approves VIMS marketability proposal for C. ariakensis

2000
CBP ad-hoc panel approves VIMS marketability proposal; Virginia Seafood Council (VSC) requests C. ariakensis introduction; Virginia Marine Resource Commission (VMRC) approves VSC request with VIMS monitoring

2001 (October)
VIMS hosts symposium on Aquaculture of triploid C. ariakensis (see report)

2001 (December)
Agencies issue statements on the use of C. ariakensis for aquaculture in Chesapeake

2002
Maryland legislature passes bill calling for research on C. ariakensis

National Academy of Sciences agrees to review C. ariakensis issue

The Controversy:
Is It Time for a Non-Native Oyster?

In limited field trials, Crassostrea ariakensis, a species native to China, has given strong evidence that it is much hardier than the Bay's Eastern oyster when it comes to battling disease. In comparative growth studies between the two in Virginia, and more recently in North Carolina, C. ariakensis was not only able to fend off MSX and Dermo but grew substantially faster and larger than the native would have if it wasn't being killed off by the diseases.

The Virginia studies were conducted in accordance with protocols of the International Council for the Exploration of the Seas (ICES) that require using second generation offspring of non-native broodstock - this minimizes the introduction of new pathogens and parasites. (Eugene Burreson of VIMS has pointed out, however, that ICES protocols cannot protect against exotic viruses.) Importantly, the young oysters were rendered infertile in the hatchery using a chemical technique that gives them three chromosomes. In August 2000, sixty thousand triploid seed oysters were distributed to Virginia growers who reared them under different salinity conditions in various confinements, including corrals, floating cages and sunken trays. Easy retrieval of all oysters was critical - studies by Allen and others have shown the capability for a small proportion of chemically-induced triploids to revert to diploids and therefore to become potentially reproductive.

It is the outcome of the Virginia trials that has created so much excitement about C. ariakensis as a complement, if not an alternative, to the Bay oyster. "None of us is against our native oyster," says Virginia waterman George Washington. "The Virginia Heritage program promised a tenfold increase [but] the oyster industry can't wait another ten years or even this year. I want to save the native oyster," he says, "but I want the industry to be around when we do."

Earlier in 2002, the Virginia Seafood Council proposed testing one million C. ariakensis at 39 locations in Virginia's portion of the Chesapeake between June 2002 and May 2003. An ad-hoc panel of the Chesapeake Bay Program's Living Resources Committee recommended not approving the request on a number of grounds. A major factor, though not the only one, was that the chemical method for inducing sterility may not be permanent; an alternative method that uses tetraploids, or animals given four chromosomes, has less risk, though that technique could not have furnished a million oysters for the trials.

While watermen and processors make a compelling case for growing C. ariakensis in the Chesapeake, there are a host of biological and ecological concerns about the impacts of a non-native oyster - and policy makers, sympathetic though they may be to the industry's plight, have been unwilling to give the green light until there is some assurance of just what those impacts might be. Will C. ariakensis survive throughout the Bay and how might it affect other species, especially the native oyster? Will it build reefs? Is it likely to be resistant to local predators, pests and diseases? If it grows so fast and so large, will it concentrate more pathogens than the native does?

In experiments conducted at VIMS, Mark Luckenbach found that juvenile Bay oysters were more competitive than C. ariakensis, as measured by increases in shell length and weight. Under these conditions, he says, C. virginica grew faster and had higher survival. When C. virginica were present, C. ariakensis had poorer survival and grew more slowly. These findings were conducted under laboratory conditions and carried only to the juvenile stage; nor do they account for the effects of MSX and Dermo, Luckenbach points out. This is to say that these and other findings cannot be extrapolated to field conditions.

Because of the ecological uncertainties on the one hand and the demands of the industries in Maryland and Virginia on the other, agencies and organizations in the Bay region have partnered in commissioning a study by the National Academy of Science_(NAS) to assess the ecological and economic issues of introducing C. ariakensis into Chesapeake Bay. Under consideration are (1) the risks and benefits of aquaculture of triploids, (2) introduction of reproductive diploids, or (3) no introduction at all. The NAS recommendations are due by August 2003.

Maryland vs. Virginia - Differences of Opinion

While there is strong resistance by federal and state decision makers to importing non-native oysters capable of reproduction, there has been a strong policy, if not philosophical, divide between Maryland and Virginia. As Jack Travelsted of VMRC has observed, "Virginia is at the more liberal end of the [introduction] spectrum."

In 1995, with the decline of the Virginia oyster industry impacting so many Bayshore communities, the General Assembly authorized VIMS to develop strategic plans for evaluating non-native species - those plans centered on the Pacific oyster Crassostrea gigas and the Suminoe C. ariakensis. C. gigas, which is native to Japan, is the dominant commercial species throughout the world - it was first imported to the U.S. northwest early in the twentieth century and is the basis of the industry there, as it is in France, England, Australia and much of New Zealand.

In contrast to Virginia, the state of Maryland until late this year has actively rejected consideration of importing a non-native oyster. While ecological uncertainty may be a key reason, there has also been a belief in Maryland that its lower salinity waters offer greater potential for restoration of C. virginica, though the last several years of low rainfall have increased Dermo and MSX and caused heavy oyster mortalities. With harvests once more on the downturn and the strong lobby for importing triploid C. ariakensis to Virginia, the Maryland General Assembly passed a bill that for the first time authorizes research on the Suminoe in order to judge its benefits for aquaculture.

As divided as Maryland and Virginia have been on the issue of pursuing the potential of a non-native oyster, they have also been divided, historically, on the management of their oyster fisheries. While watermen in both states have always harvested public grounds, much of Virginia's production (until disease became so rampant) derived primarily from businesses and independent watermen who grew oysters on private leaseholds in the Bay and its tributaries. Maryland's production, however, derived primarily from wild harvests, with private leaseholds - though acre for acre considerably more productive than public grounds - contributing very little.

Early in the twentieth century, both states had their public oyster grounds surveyed - the Yates Survey in Maryland and the Baylor Survey in Virginia identified nearly 500,000 acres of grounds that supported or at one time supported natural oyster populations. These grounds were then legally closed to leasing for oyster cultivation. The only leasable grounds available in both states were those on which oysters had never grown naturally. While both states had laws that made leaseholds available, Virginia promoted leases and made it legal for businesses to obtain them. Though numbers of Maryland watermen held leaseholds, for the most part watermen in the state opposed them and were instrumental in legislation that prohibited businesses from obtaining leases. As a result, oyster farming in the state has always been negligible.

Just as Maryland and Virginia have been divided, historically, on the management of their oyster fisheries, they are divided on whether or not to introduce a new oyster species.

While many watermen in Virginia had small leaseholds, from one to ten acres, says Mike Oesterling of VIMS, the biggest lessors were packers. It is they who could afford to shell their bottom grounds so that seed oysters brought in from the James River, the Great Wicomico or other areas would not sink.

Shelling could be expensive. "Some packers had leases that got reliable strikes [of spat] regularly, after they put down shell," Oesterling says, "so they could even produce their own seed." If you harvest the same ground year after year, eventually it will soften up, so you'll have to shell the bottom to stabilize it again. "Packers had husbandry plans," he says. "They were farmers."

In both states, oystermen could only harvest public grounds during the open Virginia season (generally October to April) - leaseholders, however, could harvest their grounds all year round. In effect, Virginia packing houses and the small number of growers in Maryland had a 12-month industry, with oysters largely from the Chesapeake. The history of leaseholds and cultivation in Virginia is a primary reason that the Virginia Seafood Council, which represents packers and other leaseholders, requested authorization to grow one million triploid Suminoes. Though seafood processor Tommy Kellum would like to see reproducing C. ariakensis in the Bay, it is only the triploids that he is now concerned with getting authorization to raise. Because leaseholds and cultivation have a relatively small niche in Maryland, watermen in the state have opposed the use of triploids and have called for introducing diploids. "If Virginia is successful using triploids," more than one waterman has said, "C. ariakensis will be introduced in Maryland."

"I wouldn't have said this five years ago - we've lost our oyster," says Larry Simns. "Talking of disease-resistance is pie in the sky. And I don't even want to talk about triploids. Maryland and Virginia need to do this together," he argues, "we need to go to diploids." How harmful can they be, what is the risk, Virginia waterman George Washington asks rhetorically. "We don't have any oysters to have a risk."

To Release or Not to Release a Non-native?

If reproducing C. ariakensis were brought into the Bay, what are the worst-case concerns, even if they were introduced adhering strictly to ICES protocols? Would they introduce a new disease or new parasite? Would they displace C. virginica from some part of its range? If they grew really well, could they cause a fouling problem? Are there potential food web effects that cannot yet be predicted? What impact would boring sponges, cownose rays, crabs and other predators have? What is the disease tolerance under different conditions?

Scientists in China, for example, where the Suminoe has long been cultured, reported that since 1992 a series of mortalities, usually from February to May, occurred along the coast of the Pearl River valley, killing about 80 to 90 percent of affected oyster populations. Scientists found a "new intracellular microorganism in the tissues of diseased oysters" that has not yet been identified.

In France, where C. gigas is the basis of the entire industry, researchers are interested in other species such as C. ariakensis because of the potential for catastrophic mortalities of C. gigas from disease. The aim was to test the Suminoe's ability to adapt to local conditions. According to a scientific paper in Diseases of Aquatic Organisms, the oysters, which were maintained in laboratory quarantine, experienced some mortalities seven months after importation: nine of the dead oysters harbored a protozoan parasite that was never before reported to occur in the Crassostrea genus. As a result, the authors concluded, the Suminoe "is not considered to be a suitable substitute for C. gigas in France."

If large numbers of triploids are approved, could this lead to the introduction of an unknown parasite? Will an easing of restrictions lead to illegal introductions? On the other hand, could triploids spur the growth of a private aquaculture industry in Maryland so that watermen could both harvest native oysters that survive on public grounds and also farm triploid C. ariakensis on leased grounds? Farming oysters is more costly than harvesting public grounds and may not be economically feasible to produce for shucking houses, the traditional market for Bay oysters. The northwest may serve as a model where the half-shell market has been increasing dramatically: according to the Pacific Oyster Growers Association, 50 percent of the oysters produced in the northwest went for shucking a decade ago; today, 75 to 80 percent are destined for the unshucked market of bars and restaurants.

What is the potential for C. ariakensis to become established if it was brought into the Bay? "Given its rapid growth and resistance to disease, if a sufficient number of reproductively-capable animals are present, establishment does seem likely," says Luckenbach.

Since June, the National Academy of Science committee has heard from industry, scientists and state and federal agencies. In the months ahead, it will be sorting through all that is available - in reaching its recommendations, it will have to navigate the rocky waters between ecological uncertainty on the one side and socioeconomic demands on the other.

For More Information

Books

W.K. Brooks. 1996. The Oyster. Baltimore, Maryland: The Johns Hopkins University Press. Introduction by Kennedy T. Paynter, Jr. Original work published in hard cover edition by The Johns Hopkins Press, 1891. Revised edition, 1905.

E. Hallerman, M. Leffler, S. Mills and S. Allen, Jr. 2002. Aquaculture of Triploid Crassostrea virginica. A Maryland and Virginia Sea Grant Publication. Available from Maryland Sea Grant. (www.mdsg.umd.edu/oysters/exotic/workshops.html)

M. Leffler. 1999. Restoring Oysters to U.S. Coastal Waters: A National Commitment. A Maryland and Virginia Sea Grant Publication, in cooperation with the National Sea Grant College Program.

V.S. Kennedy, R.I.E. Newell and A. Eble, Jr. 1998. The Eastern Oyster: Crassostrea virginica. Maryland Sea Grant College Program. College Park, Maryland. (www.mdsg.umd.edu/store/books/Oyster) V.S. Kennedy and L Breisch. 1981. Maryland's Oysters: Research and Management. Maryland Sea Grant College. (www.mdsg.umd.edu/oysters/)

R. Mann and A. Rosenfield. 1992. Dispersal of Living Organisms into Aquatic Systems. Maryland Sea Grant College Program. College Park, Maryland.

M.W. Luckenbach, R. Mann and J.A. Wesson, eds. 1999. Oyster Reef Habitat Restoration: A Synopsis and Synthesis of Approaches. Virginia Institute of Marine Science, College of William and Mary, Williamsburg.

Websites

Virginia Oyster Heritage Program (www.deq.state.va.us/oysters/homepage.html)

Maryland Sea Grant (www.mdsg.umd.edu/oysters)

Virginia Institute of Marine Science (www.vims.edu)

Virginia Institute of Marine Science, C. ariakensis (www.vims.edu/abc/CA.html)

National Academy of Sciences (www.nationalacademies.org)

This page was last modified October 03, 2019