Predation upon Mytilus galloprovincialis (Mollusca: Bivalvia: Mytilidae) by juvenile Carcinus maenas (Crustacea: Decapoda) using mandibular chipping

Field observations of small (<20 mm) individuals of Mytulus galloprovincialis at Littlehampton (West Sussex) on the south-eastern coast of England showed that many collected as recently dead shells had a distinctive pattern of damage around the posterior valve margins. Laboratory experiments confirmed that small Carcinus maenas (<22 mm carapace width) were capable of inflicting a similar style of damage. Small C. maenas fed successfully on a range of mussel sizes (5–20 mm shell length), positively correlated with carapace width. All used the same technique to access the bivalve prey, that is, by marginal mandibular chipping in order to achieve sufficient damage to allow insertion of a chelal dactyl between the valves. Mandibular chipping has previously been reported upon from non-chelate decapods and juvenile lobsters. The chelae of juvenile C. maenas are small and have a lower mechanical advantage than has been reported upon for adult conspecifics which, in any case, are not highly adapted for durophagy. We suggest that because of the poor mechanical performance and small gape of the chelae juvenile C. maenas behave as though they were achelate. As well as broadening our understanding of the repertoire of known feeding behaviours of C. maenas, our study may also provide an insight into the evolution of durophagy within the Decapoda.