Meeting Abstract
To balance energy expenditures on predator avoidance and deterrence with critical life history functions such as energy acquisition, growth, and fecundity, many prey organisms use plastic responses to predation risk that are employed when risk of injury or death is imminent. Oysters are preyed upon by numerous species and react to predatory threats by altering their shell morphology at a cost of producing less gonad tissue. We tested oyster responses to predation risk in the field and measured chemical changes in shells when blue crab predators were present. As previously reported from laboratory investigations, oyster spat grew broader, flatter, heavier, and significantly stronger shells in treatments with blue crabs. Oysters in crab treatments had significantly greater amounts of inorganic material in their shells. In contrast, control oysters had significantly greater organic matter in their shells, suggesting that they alter their shell growth by switching from organic to inorganic shell production to increase shell strength. We tested oyster morphological responses to various risk cues including injured con and heterospecifics as well as blue crabs reared on different diets. Oysters grew heavier, stronger shells in response to cues from injured prey and well as blue crabs, with the strongest shells occurring in treatments with blue crabs fed live oysters. Oyster shells were stronger than controls but weaker than in the treatment with blue crabs fed live oyster after exposure to injured prey cues as well as to crabs consuming a diet of dead tissue. Thus, oysters can differentiate between different types of risk cues, including those released by predators vs. scavengers and also react to alarm cues from sympatric prey.
