Abstract
Organisms may adjust characteristics such as behavior or morphology to reduce predation risk, but in doing so suffer reductions in growth and fecundity. To balance conflicting needs of reducing risk with energy acquisition and growth, organisms often limit expression of predator avoidance or deterrence to situations where predation risk is high. Chemical cues are often used for risk evaluation and are known to cause changes in behavior and morphology for a variety of species. We investigated morphological changes in Eastern oysters (Crassostrea virginica) in response to chemical cues from two common predators, blue crabs (Callinectes sapidus) and oyster drills (Stramonita haemastoma). We evaluated changes in shell morphology including size and strength and also assessed how morphological changes affected oyster survival in laboratory feeding assays and when exposed to a natural suite of predators. After 6 weeks, oysters exposed to both predators had significantly stronger shells. In laboratory feeding assays as well as in the field, oysters grown with either blue crabs or oyster drills had significantly lower mortality (~20%). These findings indicated that oysters use phenotypic plasticity to reduce predation risk, suggesting that predator-induced changes in oysters may be a viable strategy for improving oyster reef restoration.
