The risk assessment capability and defense induction strategy of the Eastern Oyster Crassostrea virginica

Prey respond to predation risk by implementing defensive mechanisms such as avoidance behavior, interrupting the periodicity of their life history, and altering their morphology. Prey employ defensive mechanisms at a cost to traditional fitness strategies such as growth or fecundity. The severity of response is correlated with the level of risk the organism perceives. In the marine environment, chemical cues play a large role in prey risk assessment, especially in bivalves. I tested the morphological response of oysters (Crassostrea virginica) to blue crabs (Callinectes sapidus) reared on diets of mud crabs (Panopeus herbstii) or conspecific oysters to measure the differential response of C. virginica to intraguild predation and conspecific cues. I hypothesized that oysters exposed to the exudate of blue crabs consuming mud crabs, a natural oyster predator, would respond by growing stronger, heavier shells, but that oysters exposed to blue crabs consuming oysters would grow shells that were significantly stronger and heavier. Oysters exposed to the oyster cue grew significantly lighter but stronger shells than oysters exposed to mud crab (intraguild) cues and controls. Intraguild cue oysters produced the smallest and weakest shells, but maintained a shell weight intermediate to oyster cue and control groups. The results support the hypothesis in part due to the significant increases in strength of the oyster cue treatment, but their low weight was unexpected, as was the reaction seen in the mud crab cue treatment.