In December 2003, the Scientific and Technical Advisory Committee of the Chesapeake Bay Program convened a workshop, which was attended by more than 60 scientists and managers from throughout the United States, to identify and prioritize the research required to evaluate the ecological risks and benefits of introducing diploid (reproductive-capable) Crassostrea ariakensis into the Chesapeake Bay. The impetus for the workshop was the proposal by the states of Maryland and Virginia to introduce and establish reproductive populations of this nonnative oyster species.
A year after the federal Environmental Impact Statement development process was launched, and with the potential for a decision to proceed with an introduction of C. ariakensis late this spring, it seems important to review the major conclusions and recommendations of the workshop.
Perhaps the most important conclusion was that neither the potential risks nor the potential benefits of an introduction of C. ariakensis to the Bay are adequately known.
We do not know whether there is a greater likelihood of successful oyster restoration using the Oregon population of C. ariakensis or using wild or disease-tolerant strains of native oysters.
The risks that C. ariakensis might pose to native oysters or other organisms within the Bay, and in regions outside the Chesapeake, are not well understood. Similarly, what ecosystem services—such as water filtration or fish habitat—might be provided by C. ariakensis relative to the native C. virginica and whether the Asian oyster is a suitable replacement for native oysters for fisheries are not known.
Finally, we do not know whether human health risks for the consumption of C. ariakensis are the same as native oysters.
Given the uncertainty surrounding the potential risks and benefits of an introduction, three issues on which participants determined there was already sufficient evidence to reach a conclusion without additional research are critical to highlight:
An introduction of diploid C. ariakensis is likely to be irreversible. In reaching this conclusion, the STAC workshop concurred with the National Research Council Report. Even on land, where animals can be highly visible, it can be extremely difficult, and often impossible, to eliminate nonnative species that are well-adapted to grow and reproduce in the environment to which they have been introduced.
The difficulty of distinguishing small C. ariakensis from juvenile native oysters, the low probability that all adult C. ariakensis could be located underwater and removed, and the ability of oysters to spread within the Bay beyond their site of introduction through larval dispersal would likely make it impossible to eliminate this nonnative species if it were introduced and thrived in the Chesapeake Bay.
The spread of C. ariakensis beyond the borders of the Chesapeake Bay is inevitable if a self-sustaining population is established. The hope of agencies proposing the introduction of C. ariakensis to the Chesapeake is that it will be well-adapted to grow, reproduce and spread beyond the specific reefs on which it is placed, thus filling the ecological and fisheries roles that native oysters once played.
Substantial evidence from the patterns of spread of other nonnative estuarine species makes it a virtual certainty that C. ariakensis, if successful in the Bay, will spread to other estuaries. Research will therefore need to consider the risks of a C. ariakensis introduction outside the Chesapeake Bay
The ‘Oregon population’ of C. ariakensis stems from a very few individuals; the breeding population may have been represented by as little as six or fewer adults. Therefore, the genetic diversity is very low. Low genetic diversity within a population can result in most or all of the individuals having similar susceptibility to predators and parasites, and is generally not a desirable trait for species used in ecological restoration. An extreme example of the potential problems of low genetic diversity can be seen in agricultural crops. In high intensity agriculture, new strains continually need to be developed to overcome the race between the crops and their pests and diseases.
Although the genetic diversity of the initial introduction of Oregon C. ariakensis could be increased by a later introduction of strains from Asia, it is not clear where the best source population for such animals is located.
There is also considerable taxonomic confusion in field identifications of oysters within the native range of C. ariakensis, and it is not clear which population would be best suited for the physical and biological environment of the Chesapeake. It is not clear which, if any, Asian population of C. ariakensis forms the extensive, ecologically complex reef systems that native oysters have created in the Bay.
A fourth conclusion points to the need for disease research that extends beyond simple tests of the susceptibility of C. ariakensis to the two pathogens that have decimated oysters in the Chesapeake Bay. The potential for novel interactions between oyster pathogens—those resident in the Bay and others that may emerge—and C. ariakensis is uncertain and impacts may be unpredictable for both this oyster and other species over time. It is important to consider the potential that C. ariakensis might be susceptible to pathogens that do not affect native oysters, as well as to serve as a host for pathogens that are not currently problematic in the Bay.
The STAC Workshop participants estimated that 5 years will be needed to generate sufficient information to reduce the uncertainty surrounding risks and benefits of introducing C. ariakensis.
This is in close agreement with the conclusion of the National Research Council report, and is a number arrived at with substantial restraint on the part of the research community. This time frame—considered the minimum needed—will require a massive marshaling of effort by researchers, the construction of quarantine facilities, an infrastructure to produce oysters and sufficient funding to conduct research.
Given the dismal state of the oyster fishery in the Chesapeake Bay, there is an understandable desire to complete the required research as quickly as possible so that a decision on whether an introduction should go forward can be made. There are important limits, however, to how quickly the needed data can be acquired.
For instance, sufficient numbers of C. ariakensis must be spawned and reared for use in studies that evaluate the performance and risks of oysters that are several years old—not just juveniles.
In addition, there is a wide range of environmental conditions to which oysters in the Bay are exposed, as well as a variety of ecosystem and fisheries functions considered critical by both the public and the fishery.
The effect of any single nonnative species, including oysters, can range from economically beneficial to economically and ecologically harmful across the variety of locations in which it becomes established. Yet most research done to date has been extremely limited in scope, addressing only a small subset of the Chesapeake Bay environment, and an even smaller subset of the Atlantic Coast environment.
Tests of the ecological and fishery value of diploid C. ariakensis will require multiple age classes, and in some cases, large numbers of individuals. Tests on small numbers of juveniles are simply not adequate.
It is also important to recognize that research is often a sequential process—directions are determined by early findings.
And finally, as with any venture—scientific or otherwise—experiments don’t always work the first time they are attempted. Pipes break, oysters don’t spawn when needed, and standard procedures can fail.
The question of how much risk is acceptable, what kinds of risks are acceptable and how much benefit is required to make risks acceptable, are policy decisions, not scientific decisions.
What research can do is to identify and help to quantify the risks and potential benefits so that decisions can be made based on a firm foundation of facts.
Gathering the needed information will take time, funding and commitment from all stakeholders concerned with the restoration and protection of the Chesapeake Bay.