Aquaculture of Triploid

Crassostrea ariakensis
in Chesapeake Bay

A Symposium Report

The Eastern oyster, Crassostrea virginica, was for three centuries the object of a major fishery in the Chesapeake Bay. In 1957, the protozoan parasite Haplosporidium nelsoni spread MSX disease southward from Delaware Bay to the lower Chesapeake Bay, devastating native populations of the eastern oyster. By the 1970s, MSX had wiped out vast tracts of oysters on Virginia's high salinity grounds. Through the 1980s, MSX was joined by a second virulent parasite, Perkinsus marinus (the cause of Dermo disease), which also began killing oysters. Dermo was thought to be limited to salinities greater than 15 parts per thousand (ppt); however, by the 1980s, it began to appear in lower salinity waters of 10 to 12 ppt. Together, both diseases have frustrated restoration and aquaculture efforts and have brought the Bay oyster fishery to near ruin, especially in Virginia. The immense loss of oysters and their capacity for filtering algae is likely to have contributed to the decline of water quality in the Bay. In addition, the entire industry is in jeopardy, as much of the infrastructure for processing and packing oysters could fold for lack of product.

During the late 1980s, several baywide workshops were convened in the mid-Atlantic region to explore the options for countering the impacts of disease. These workshops, which brought together resource managers, policy makers, scientists, commercial fishermen, aquaculturists and concerned citizens, focused on specific topics, among them, research needs to combat MSX and Dermo, socio-economics issues related to the oyster industry, and the ecological and genetic implications of introducing non-native oyster species. Another workshop focused on the implications of introducing Crassostrea gigas, then the major non-native oyster candidate (Synopsis of the Oyster Ecology Workshop 1991; Leffler and Greer 1991). The goals were to: (1) evaluate how C. gigas introductions affected ecosystems around the world; (2) provide an overview of the ecological factors that would affect the growth of C. gigas in the Bay; and (3) assess the ecological risks and benefits of its introduction in mid-Atlantic waters. The symposium reported on here occurred 10 years later, almost to the day. Clearly, interest in the use of non-native oysters persists.

In 1995, the Virginia General Assembly took a more directive approach to non-native oyster research. It charged the Virginia Institute of Marine Science (VIMS) to submit and initiate a strategic plan for evaluating non-native species; VIMS submitted the plan in 1996. Field studies began with C. gigas. Native to Japan, it had been imported to the U.S. west coast early in the century, where it has since been the mainstay of the industry that depends entirely on hatchery production of oyster seed. C. gigas is also the basis of oyster production industries on every continent except Antarctica.

In 1997, laboratory and field trials were undertaken with C. gigas; overall, these oysters exhibited unremarkable performance in growth, disease tolerance and taste acceptability compared to the native oyster (Calvo et al. 1999). VIMS researchers then began investigations of the Suminoe oyster; also a species from Asia, Crassostrea ariakensis was first brought to the United States by growers in the Pacific Northwest. Production has been limited, largely because the region's higher salinities make hatchery culture inconvenient and more costly than for C. gigas. VIMS undertook field comparisons between infertile (i.e., triploid) C. ariakensis and the Bay's native oyster, C.virginica, between June 1998 and September 1999. Focusing on survival, growth and disease susceptibility, the results demonstrated that C. ariakensis was faster growing, reached market size in about a year (compared with the two to four years for C. virginica), and tolerated MSX and Dermo disease; furthermore, it was largely indistinguishable in taste from native oysters.

These findings suggest that hatchery-reared C. ariakensis holds promise for rebuilding the commercial oyster industry in Virginia and Maryland through aquaculture production. Furthermore, use of sterile triploids in aquaculture could greatly reduce reproductive potential. At the same time, there are concerns, if not strong reservations, over employing non-native or exotic species, when there are so many instances of their ecological impacts.

In an attempt to broadly inform Chesapeake Bay stakeholders on these issues, a consortium of institutions sponsored the Symposium on Aquaculture of Triploid C. ariakensis in Chesapeake Bay as a means for: (1) exchanging information on research findings and practical experience in Virginia (there have been no studies on C. ariakensis in Maryland) and (2) considering critical issues regarding research needs, policy and regulatory matters, and the rehabilitation of the oyster industry.

The symposium was attended by federal and state agency managers, non-governmental organization (NGO) representatives, scientists, watermen, aquaculturists and concerned citizens from Virginia, Maryland, North and South Carolina, Delaware and New Jersey. The agenda included presentations and discussions related to the biology of C. ariakensis, disease concerns, research and industry field trial results, production of triploids, a predictive risk model, strategies for minimizing environmental risk, and public attitudes about non-indigenous species. These presentations, together with poster sessions on key technical aspects of C. ariakensis research, provided a baseline of shared knowledge for three stakeholder discussion groups that represented industry, scientific, and policy and regulatory interests.

Based on the presentations, each of these discussion groups was asked to consider major concerns and issues related to the aquaculture of triploid C. ariakensis in the Chesapeake Bay. This report summarizes the outcomes of the group deliberations and key points in the discussions that followed. It also provides a synopsis of each of the presentations.