| Abstrakt: |
The decline of wild populations of the eastern oyster Crassostrea virginica from fishing impacts and disease combined with limited success in its culture has stimulated discussion among coastal managers about the risks and benefits of introducing non-native oysters in Maryland, Virginia, and North Carolina. Field experiments in 1999 to 2000 and 2001 to 2002 comparing growth, survivorship, and prevalence of disease in 2 non-native oysters, C. gigas and C. ariakensis, versus C. virginica in North Carolina estuaries demonstrated that in high-salinity (>25‰) waters, performance of C. gigas in culture greatly surpassed that of both of the other oysters (with growth 162.4% higher than C. virginica and 54.1% higher than C. ariakensis and survivorship 33.1% higher than C. virginica and 22.3% higher than C. ariakensis). C. ariakensis survivorship at these high salinity sites was highly variable and unpredictable even when using environmental covariates, and at salinities below -10‰ this species did not grow, rendering its culture nonviable at low salinity. However, in waters of intermediate salinity (15‰ to 25‰), C. ariakensis outgrew both of the other 2 oysters (35.9% higher than C. gigas and 24.5% higher than C. virginica) and exhibited 42.1% higher survivorship than C. gigas. Although survivorship of C. virginica and C. ariakensis did not differ significantly at intermediate salinities, only C. virginica failed to achieve legally harvestable sizes and, based on its increasingly high susceptibility to death from disease with age, is likely to have experienced much greater mortality by the time of complete grow-out. Experimental elevation above the bottom augmented growth and survivorship of C. ariakensis most strongly, whereas C. gigas was not influenced by rack height. Before large-scale introduction of any non-native oyster occurs, the quantitative biologic results should first be incorporated into economic evaluations that weigh expected profitability and ecosystem benefits against the potential ecologic risks of introduction (both for wild release and for aquaculture of triploids). [ABSTRACT FROM AUTHOR] |
