Aquaculture of Triploid

Crassostrea ariakensis
in Chesapeake Bay

A Symposium Report

The symposium organizers provided the three stakeholder groups with questions related to their particular interests as a means of catalyzing discussion of key concerns and issues (see Appendix 1). The groups were not constrained to considering only these questions.

While the group discussions were directed to focus on the aquaculture of triploid C. ariakensis, each group independently found that it is difficult to consider the risks of aquaculture of triploid (infertile) C. ariakensis as separate from the risks of diploid (fertile) C. ariakensis. That is, there was consensus that triploid aquaculture would inevitably lead to some introduction of reproductive individuals in the Bay, with unknown outcomes for population growth. Because VIMS data and industry field trial findings to date indicate that C. ariakensis has superior resistance to MSX and Dermo disease, can reach harvest size much more quickly than the native oyster, and appears to be indistinguishable in taste, concern was raised over the potential for unauthorized release of diploid broodstock into Bay waters.

The industry group urged scientists to begin studying the environmental and ecological impacts of diploids in the wild immediately. Scientists recommended that ecological risks of introducing diploids must be assessed over a broader geographical region than just the Chesapeake because an introduced species could potentially spread throughout the Atlantic and Gulf Coasts. Researchers in North Carolina apparently are beginning to work with field plantings of triploid C. ariakensis, and so all east coast states must be included in any discussion of a possible introduction.

Industry Discussion Group

The industry participants reported a sense of urgency about the need to move forward rapidly because the very survival of many commercial operations is at stake. The group's key conclusions are:

• If allowed to proceed with production of triploid C. ariakensis, the Virginia industry expects to produce one million "natural" triploids in the first year, and could saturate the regional market demand of 270 million oysters within five years.
  
  
• If 100% natural triploid oysters (see summary of Triploid Strategy and Risks) are unavailable, the industry would be willing to use chemically induced triploids.
  
  
• Virginia growers would be willing take reasonable measures to confine triploid oysters and to undergo a training course on how to grow biosecure oysters. Course completion could be tied to the granting of a permit for growing oysters.
  
  
• Industry members would be willing to open their production records on purchase, movement, harvest, and sale of triploid C. ariakensis product to outside scrutiny, but are not willing to share access to customer lists and financial information. Virginia growers recognize the Virginia Marine Resources Commission as the responsible agency for managing and mitigating any risks, with the Virginia Institute of Marine Science serving an advisory role.
  
  
• Virginia producers expressed solidarity with Maryland producers, who also are interested in C. ariakensis, but currently face a regulatory climate that opposes introduction of triploid C. ariakensis. Maryland producers are specifically interested in a diploid introduction and might oppose the introduction of a triploid without a concurrent plan for a diploid oyster. Their concern is that a triploid-only introduction in Virginia waters would threaten their competitive stance in the marketplace and allow Virginia to "get ahead" of Maryland. The sentiment, "Give us both or nothing," was repeated several times.
  
  
• Industry strongly encouraged an undertaking to develop a disease-free diploid stock by January 2003. The industry reasoning includes the importance of taking the long view, especially that getting oysters back on the bottom in natural oyster bars is the only viable solution for getting the industry, including processing houses, back on track. The Washington State oyster industry, which is based primarily on hatchery production, was discussed as a model of the approach and scale needed in the Chesapeake Bay.
  
  
• Although most industry participants agreed with the views summarized here, a minority favored immediate introduction of diploid C. ariakensis.

Science Discussion Group

In considering risks associated with the introduction of a non-native species, there was consensus that some risks are indeed unknowable and, hence, complete certainty regarding the risks involved may never be acheived. However, a more complete understanding of the biology and ecology of C. ariakensis would help identify these risks and perhaps assuage some of these concerns. While all risks can be avoided by not permitting the introduction of C. ariakensis, there also are risks associated with doing nothing. These include the lack of economic benefit associated with having a viable commercial oyster species as well as ongoing degradation of habitat and water quality in the Bay and other locations on the east coast that lack major oyster populations.

Adverse Risks

Potential hazards associated with the introduction of C. ariakensis were ranked from highest to lowest. Some of these hazards follow from the consensus viewpoint that the use of triploid oysters for aquaculture purposes will inevitably lead to the introduction of diploid oysters through the three mechanisms below, listed in order of severity.

• Illegal Introductions. Uncontrolled illegal introductions of diploid oysters using methods not in compliance with ICES (International Council for the Exploration of the Sea) protocols for purposes of establishing naturally reproducing oyster populations. C. ariakensis is being reared in a limited manner in at least one commercial oyster hatchery in the Pacific Northwest, using broodstock that were introduced many years ago during shipment of Japanese oyster seed. Theoretically, these oysters could be raised commercially and hence would be widely available in the seafood market in addition to being available from native stocks in China. The possibility of an illegal introduction argues for public education about this problem because it is by far the highest risk, worst-case scenario for the Bay. It also emphasizes the importance of an organized, officially controlled introduction (assuming one proceeds) under ICES protocols.
  
  
• Catastrophe. Possibility of storms and other events destroying aquaculture biosecurity measures that results in the loss of triploid oysters to the wild. There is a high probability that aquacultured triploid oysters lost through disaster, and left unharvested, could revert to diploidy and gain fertile status as they grow older. This may lead to reproductively competent oysters in the Bay (see summary on Triploid Strategy and Risks for discussion of "reversion").
  
  
• Biological/Biosecurity. Variability in the degree of triploidy (see summary on Triploid Strategy and Risks) and level of harvest success in recapturing aquaculture-planted triploid oysters (e.g., there is a risk of triploid reversion to diploidy) are hazards whose risks can be minimized in a contained aquaculture system. These risks can be reasonably well quantified using the risk model (see summary on Risk Model).

Another hazard of introducing C. ariakensis is disease transmission or opportunity.

• Disease Risk. Possibility of introducing an unknown or unidentified disease in oyster broodstock. This risk can be minimized by performing introductions under the ICES protocols, as has been done with all work on this species by VIMS. Unfortunately, there remains some risk that viruses may be transferred even when using ICES protocols. As Dr. Eugene Burreson pointed out (see summary on Disease), more testing for viruses in C. ariakensis broodstock using the latest molecular techniques will provide a higher level of assurance, although even that approach cannot guarantee that all viruses will be found. A study of diseases in the natural range of C. ariakensis in China would enable us to become cognizant of any potential diseases and parasites that this species might harbor. Such analysis also should include this species in the Pacific Northwest. Also unknown is whether C. ariakensis, as a new species in the Bay community, will prove a host for a disease not yet problematic.

Potential Scenarios from C. ariakensis Introduction

• Competition of C. ariakensis and C. virginica. Either a triploid that reverts to diploidy or an introduced diploid will have limited opportunity to compete with native C. virginica oysters in Virginia simply because of the decimated populations in Virginia's higher salinity waters. In Maryland, however, with lower salinity waters and less disease pressure, there is still hope of restoring the native species, C. virginica. (The ongoing attempts to breed and select eastern oysters that can better tolerate MSX and Dermo is an ongoing strategy to help restore oyster stocks [Restoring Oysters to U.S. Coastal Waters 1999]. Some researchers pointed out, however, that such selective breeding is altering the native species genetically, such that it may be a "native" oyster in name only.) Thus, potential interspecific competition between these two species in Maryland, and in other states along the east coast of North America, is a concern. It also is possible that there might be synergies between the two species (e.g., the recently completed field trials showed that eastern oyster larvae set and grew on the shells of triploid C. ariakensis). Certainly, the use of C. ariakensis for aquaculture could reduce fishing pressure on dwindling stocks of eastern oysters. In any event, research is needed to explore some of these possible interactions. Triploid C. ariakensis that are maintained under appropriate biosecurity measures could be used to explore some of these possible interactions in both the laboratory and field. Any such experimental work should be subject to rigorous oversight to ensure that experimental design and biosecurity concerns are met. Probably the greatest area of ignorance that needs to be addressed is how well diploid C. ariakensis will reproduce, recruit and survive under natural conditions in east coast waters. Studies of the west coast stocks may help to answer some of these questions. Even after more research, the ultimate outcomes of any introduction can never be predicted with certainty.
  
  
• Return to Benthic-Dominated Ecosystem. While there was general agreement that more oysters could restore the Chesapeake Bay to a benthic-dominated system, participants disagreed about the merits of such ecosystem-level changes. If established, widespread oyster populations likely would promote water quality and habitat benefits, including declines in gelatinous zooplankton as predicted by ecosystem-level models; however, a benthic-dominated system has the potential for reduced finfish populations. This scenario is highly speculative and should be explored among a wider range of scientists than was present in this workgroup.
  
  
• C. ariakensis a Nuisance Species? It is possible that C. ariakensis could so establish itself in the bay that oyster populations would become overcrowded, potentially resulting in small, commercially unacceptable oysters. Such high production could drive down market values. There were suggestions that if C. ariakensis became extremely prolific, it could turn into a costly nuisance, for example, fouling boat bottoms and water intake pipes; however, this argument is based on problems associated with such accidentally introduced species as the gypsy moth and zebra mussel that have escaped the natural biological controls imposed by predators in their native range. Because C. ariakensis is so similar in size, shell characteristics, reproductive mode, etc., to the native C. virginica, the suite of current predators (from humans, cownose rays, and blue crabs to the ubiquitous polyclad flatworms, Stylochus ellipticus) likely would control the abundance of C. ariakensis as was done historically for C. virginica.

Need for Risk/Benefit Analysis

There is a need to undertake a risk/benefit analysis that emphasizes an understanding of the economic and ecological consequences of having C. ariakensis introduced into the east coasts of North America. This analysis must take into account the ecological, social, and economic implications to Atlantic Coast stakeholders. For example, some groups such as watermen and processors would likely embrace an increase in oysters, whether they be C. virginica or another species, while others may object to a non-native oyster on the Atlantic Coast.

Research Support

Because of the identification of a number of research issues, it was recommended that the National Sea Grant Program's Oyster Disease Research Program (ODRP) be broadened to support research on non-native oyster species. The ODRP website is www.nsgo.seagrant.org/research/oysterdisease.

Regulatory and Policy Discussion Group

There was consensus on the need for additional resources and technical expertise for expanding the capability of looking at a "considered opinion" on the commercial use of triploid non-native oysters in the Chesapeake Bay. The group considered what is reasonable to ask and how much must be known in order to make an informed decision on whether and how to go forward with aquaculture of C. ariakensis. Key information needs for reaching defensible decisions include the following:

• More knowledge of basic species biology of C. ariakensis.
  
  
• More simulation modeling, including modeling of the economic dimension. There is a need to validate the risk model's predictions through field observations and experiments.
  
  
• A better sense of user need conflicts, for example, the effects of C. ariakensis culture on: (1) blue crabs, finfish fisheries, and boating in the Chesapeake Bay and (2) Atlantic Ocean and possibly even Gulf Coast ecosystems.
  
  
• A better sense of possible benefits to ecological function by restoration of filtering capacity using C. ariakensis.
  
  
• A better sense of the ecological consequences of introduction of the diploid C. ariakensis.

Biosecurity

Biosecurity concerns could be addressed by incorporating risk minimization strategies into the permitting process. The group discussed the possibility of including a bonding requirement in the permit. It also had an inclusive view of who should be included among the responsible parties in managing and mitigating any risks, including not just state agencies, but also federal agencies and the permittees themselves.

Maryland Opposition to Introduction of Non-Native Species

Although most participants agreed with the viewpoint of proceeding with caution, Maryland agency representatives oppose the introduction of a non-native species in any form.