MEPS 300:193-200 (2005)  -  doi:10.3354/meps300193

Cannibalistic crabs respond to the scent of injured conspecifics: danger or dinner?

Matthew C. Ferner*, Delbert L. Smee, Yin P. Chang

School of Biology, Georgia Institute of Technology, Atlanta, Georgia, 30332-0230, USA *Email:

ABSTRACT: The selective advantage of avoiding lethal predation typically outweighs the benefits of obtaining food. Many aquatic organisms reduce their foraging activity after detecting the presence of injured conspecifics, but responses of cannibalistic animals are less obvious because injury-related cues might attract rather than deter alerted consumers. We investigated the effect of injured conspecifics on the foraging responses of blue crabs Callinectes sapidus, which are ecologically important consumers known for their aggressive behavior and cannibalistic tendencies. In estuarine tidal channels, we presented natural foragers with a choice between baited control traps and baited treatment traps that included an additional odor source. Traps containing an injured blue crab captured significantly fewer blue crabs than paired control traps deployed for periods of up to 18 h. Injured blue crabs that were aged prior to trap deployment confirmed that deterrent cues related to the injury had dissipated within 22 h. Traps containing chemical solutions derived from injured blue crabs elicited avoidance by conspecifics, but neither uninjured blue crabs nor injured stone crabs Menippe mercenaria were deterrent. Together these data demonstrate that blue crabs reduce foraging activity in the presence of odors released from freshly injured conspecifics. Not only should such avoidance responses facilitate survival by distancing unharmed individuals from areas of intense conflict, but the associated changes in blue crab foraging behavior could also have broader ecological consequences through impacts on other trophic levels.

KEY WORDS: Foraging tradeoffs · Avoidance behavior · Olfaction · Conflicting cues · Alarm chemical

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