Site-specific advantages of using different species predator cues to enhance oysters for restoration and aquaculture

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Benjamin A. Belgrad, Wiliam Knudson and Delbert L. Smee, Dauphin Island Sea Lab, Dauphin Island, AL, Sarah Roney, Georgia Institute of Technology, Atlanta, GA, William C. Walton, Auburn University Shellfish Laboratory, Dauphin Island, AL, Delbert L. Smee, Marine Science, University of South Alabama, Mobile, AL

Background/Question/Methods
Induced defenses are a common response of prey in the presence of predators to reduce their risk of being consumed, but the effectiveness of these defenses among different predators or natural conditions is not well understood. We tested whether exposure to cues from two common predators could increase the survival of oysters, Crassostrea virginica, under aquaculture scenarios and quantified the extent mortality varied with cue source and environmental conditions. Juvenile oysters cultured in a flow-through system were exposed to either caged blue crabs, Callinectes sapidus, caged oyster drills, Stramonita haemastoma, or empty cage controls for one month then placed at seven sites for 1 – 14 weeks. We compared the shell crushing force and morphology across predator exposure treatments and individual oyster survival across sites and treatment.
Results/Conclusions
Oysters grown with blue crabs had 15% larger shells than controls while oysters exposed to drills were 5% larger. Conversely, oysters exposed to drills had the strongest relative shell strength as their standardized crushing force was 55% stronger than controls whereas blue crab exposure produced 47% stronger shells. These changes in shell characteristics produced markedly different survival patterns across sites with survival probability varying from controls by -0.75 – 617% after a week in the field. Exposure to blue crab cues usually caused the greatest increase in survival probability across site. However, oysters in sites with high amounts of drills had the highest survival probability when they were exposed to drills in the nursery, indicating that induced defenses are species specific and that the survival benefits of cue induction may be maximized when cue exposure is paired with predator regime. Overall, our findings demonstrate the utility of using predator cues in the industry to enhance the survival of oysters for restoration operations and provide insight into the evolutionary dynamics of phenotypic plasticity.