USING CALCEIN, A FLUOROCHROME CHEMICAL TAG, TO MARK SHELLS OF THE EASTERN OYSTER, CRASSOSTREA VIRGINICA, AND TO VALIDATE DIRECT SETTING OF OYSTER LARVAE

Effective management of fisheries necessitates the advent and use of tools to monitor wild and introduced species. Tools currently available for marking shells of eastern oysters (Crassostrea virginica) predominantly rely on the physical handling of individual organisms and do not lend themselves to labeling large numbers of individuals with a durable tag. To test and apply an effective mass-marking tool for C. virginica, this research focused on 1) determining the efficacy of chemical labeling of multiple life stages of C. virginica using calcein, a fluorochrome dye, and assessing the potential impacts on survival and growth, and 2) identifying if the larval marking method could be used to validate the direct setting method of oyster stock supplementation that involved releasing larvae onto suitable habitat in situ. To investigate objective 1, multiple life stages of C. virginica were exposed to calcein immersion baths and tracked over time in laboratory experiments. Objective 2 was investigated through an applied field experiment that released calcein-tagged larvae onto constructed artificial reefs that were recovered and assessed for the presence of tagged juveniles. Results from labeling all life stages indicate that C. virginica readily incorporate calcein into shells with minor effects on settlement, growth, and survivorship at concentrations of 25 and 50 mg l-1 for larvae and 250 mg l-1 for juveniles and adults. These marks could be seen without sacrificing individuals, were visible on the shells of juveniles for at least four years, and were retained on the shells of pediveliger larvae for four weeks post metamorphosis. Calcein had little to no effect on the survival of most juveniles and adults and had no effect on the settlement rates of larvae. Field deployments of marked larvae on artificial reefs in the Tred Avon River showed that marked larvae were recovered in high concentrations at release sites, indicating that ‘direct setting’ of pediveligers onto shell bags in situ is possible without enclosures. This is the first known successful test of direct setting of C. virginica pediveliger larvae in situ that was verified with chemical mark and recapture methods. These findings have wide application for supporting C. virginica research, restoration efforts, and industries: these techniques could be used to strengthen comparative growth studies, validate larval transport models, evaluate stock enhancement activities, support law enforcement efforts, and enable testing of alternative setting strategies