Predatory interaction between the brachyuran crab Cancer pagurus and decapod crustacean prey

Abstract

In laboratory experiments Cancer pagurus successfully subdued a wide size range of decapod crustaceans (conspecifics, Galathea squamifera, Pilumnus hirtellus, Pisidia longicornis, and Porcellana platycheles). Mishandling by C. pagurus, prey retaliation, and prey limb autotomy contributed to attack failure. A simple grab response dominated the pursuit phase of predatory interaction, although C. pagurus also pounced on, and actively stalked, decapod crustaceans. Handling times, Th, were long (up to 1.44 h), due to an extended consumption phase. By comparison, involvement time, Ti, in unsuccessful predation attempts was much shorter (median Ti < 180 S for all prey species). Profitability (prey energy content (kJ)/Th) increased linearly with prey size for one size class of C. pagurus feeding on P. platycheles. Due to incomplete consumptlon, energy intake [kJ predator-' d-l) from an unrestricted d ~e t of P platjrcheles was considerably lower than numerical predation and whole prey energy content ~vould suggest. Nevertheless, decapod crustaceans proved to be energetically valuable, if somewhat eluslve, prey for C. pagurus. Predation success rate of C. pagurus on P. platycheles was < 0.5 in open encounters. However, when prov~ded with shelter. C. pagurus adopted ambush predation techniques to capture P. platycheles, thereby compensating for the relatively low predation success observed in open encounters with this decapod crustacean prey.