Claw morphology and prey consumption rates of two estuarine crab species were compared: the introduced European green crab, Carcinus maenas, and the native Dungeness crab, Cancer magister. For crabs of similar weight, both the crusher and cutter claws of C. maenas were larger and exhibited higher mechanical advantage values of the claw lever system than C. magister. The mechanical advantages of C. maenas crusher and cutter claws are 0.37 and 0.30 respectively versus 0.25 for the claws of C. magister. To evaluate the feeding rates of similar-size crabs of each species on prey varying in shell thickness, we conducted laboratory feeding trials. Each crab was offered thin-shelled mussels (Mytilus trossulus, 30–40 mm) or thicker shelled native oysters (Ostrea lurida, 40–50 mm), and the number of consumed prey items was recorded. When offered mussels, subadult C. magister ate significantly more prey per day (7.2 prey/day) than adult C. maenas (5.4 prey/day). However, when crabs were offered harder shelled native oysters, C. maenas, with their more robust claws, were more capable of crushing them than C. magister, with their more delicate claws. Although C. maenas is competitively dominant to similar-size juvenile C. magister, the per capita feeding rate and predatory impacts of these 2 species depends on prey type.
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Vol. 29 • No. 2