Behavior and morphology of Nucella lapillus influenced by predator type and predator diet

To reduce their risk of being eaten, prey may change their morphology or behavior in response to predators, which can result in slower growth and lower fitness. To minimize costs, prey limit anti-predator responses to risky situations, which requires prey to reliably detect cues indicative of predation risk. The purpose of this study was to ascertain how different types of risk cues would affect the multiple responses of a common prey organism. Using the dogwhelk Nucella lapillus as a model, we compared behavioral and morphological responses of dogwhelks to green crabs Carcinus maenas and rock crabs Cancer irroratus when fed diets of conspecific dogwhelks or of marsh periwinkles Littorina littorea, a heterospecific grazing snail. We noted a significant reduction in dogwhelk movement in the presence of both predators, with green crabs causing a significantly greater reduction in movement than rock crabs. Dogwhelks were then exposed to cues from crabs maintained on diets of either dogwhelks or periwinkles continuously for 45 d, and we measured changes in dogwhelk foraging rates on mussels (Mytilus edulis) weekly during the 45 d exposure, as well as dogwhelk growth. Predator cues suppressed dogwhelk foraging, but regardless of predator type, dogwhelks consumed fewer mussels when predators were eating dogwhelks. Dogwhelks grew significantly less when exposed to crabs consuming injured conspecifics, but growth was unaffected by predators when they were fed periwinkles during induction treatments. These results indicate that cues from both predators and injured conspecifics are used by dogwhelks to evaluate predation risk and that the injured conspecific cue in combination with that of a potential predator causes a greater response than does that of the predator alone. It is necessary to assess multiple types of risk cues and prey responses when studying nonlethal effects predators have on prey because the type and magnitude of prey responses can vary with the type of risk cues detected.