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A field study of blue crab responses to conflicting chemical cues.
Ferner, Matthew*,1, Smee, Delbert1, Chang, Yin1, 1 School of Biology, Atlanta, Georgia, USA
ABSTRACT- Animals must often balance the conflicting demands of resource acquisition and predator avoidance. In aquatic habitats where visual cues are limited, dissolved chemicals can provide useful information about the location of food and the proximity of predators or conspecifics. Chemical alarm signals released by threatened or injured prey act to warn other animals of danger and may permit alerted individuals to alter their morphology, physiology, or behavior in order to reduce vulnerability to predation. Behavioral responses to alarm signals include fighting, fleeing, or concealment, all of which could compromise foraging success. Our field study of blue crab behavior in estuarine tidal creeks revealed a trade-off between responses to feeding attractants and alarm pheromones. Baited traps containing an injured crab caught significantly fewer foraging crabs than baited traps alone. Aging the injured crabs for various periods of time before trap deployment confirmed that alarm signals discourage foraging for at least 8 hours but are no longer deterrent after 22 hours. Additional field tests confirmed that the alarm signals are both chemical and species-specific. These data demonstrate that blue crabs will sacrifice foraging opportunities when confronted with the scent of freshly injured conspecifics. Not only should such responses to alarm pheromones facilitate predator avoidance, but associated changes in movement or habitat use could have more far-reaching ecological consequences. For example, if crabs are conditioned to spend less time foraging or to avoid high-risk habitats, these same areas may provide a refuge for their own prey (e.g., bivalves). On the other hand, crab predators (e.g., birds) may forage more successfully in areas where the effectiveness of alarm pheromones is confounded by hydrodynamic mixing or by elevated background stimuli. Manipulative field studies of animal responses to multiple chemical cues should help to clarify the processes that regulate trophic interactions within natural communities.
Key words: Callinectes sapidus, foraging, alarm pheromone, chemosensory