Prey selection by Gulf of Maine green crabs (Carcinus maenas), rock crabs (Cancer irroratus) and American lobsters (Homarus americanus): A laboratory study

Young green crabs (Carcinus maenas), rock crabs (Cancer irroratus) and American lobsters (Homarus americanus) co-exist in close proximity and forage on similar prey species in the rocky intertidal in the Gulf of Maine. Young green crabs (25-35 mm carapace width), rock crabs (25-35 mm carapace width) and American lobsters (25-35 mm carapace length) were collected along with the prey species blue mussels (Mytilus sp.), rock barnacles (Semibalanus balanoides) and common southern kelp (Saccharina latissima) from the rocky intertidal of the southern section of Saco Bay in the Gulf of Maine. Claw measurements were taken, prey size and prey species preference was tested and caloric value of prey was determined. Morphological measurements indicated that all three decapod species had different sized chela relative to body size. In the laboratory, the three predators preferred similar sized mussels and barnacles, and had similar handling times for both of these prey species. None of the three predator species consumed measurable amounts of kelp. Rock crabs and lobsters preferentially selected mussels over barnacles, while green crabs consumed equal amounts of both prey species. The preferred mussel size was smaller than the calculated optimum while the optimal barnacle size was eaten. These results suggest that while green crabs, rock crabs and lobsters have differing claw morphologies, they select similar prey and consume prey at the same rate.