The invasive green crab and Japanese shore crab: behavioral interactions with a native crab species, the blue crab

Blue crabs, Callinectes sapidus (Rathbun), are an ecologically and commercially important species along the East coast of North America. Over the past century and a half, blue crabs have been exposed to an expanding set of exotic species, a few of which are potential competitors. To test for interactions with invasive crabs, juvenile C. sapidus males were placed in competition experiments for a food item with two common non-indigenous crabs, the green crab Carcinus maenas (L.) and the Japanese shore crab, Hemigrapsus sanguineus (De Haan). Agonistic interactions were evaluated when they occurred. In addition, each species' potential to resist predators was examined by testing carapace strength. Results showed that C. maenas was a superior competitor to both C. sapidus and H. sanguineus for obtaining food, while the latter two species were evenly matched against each other. Regarding agonism, C. sapidus, was the "loser" a disproportionate number of times. C. sapidus carapaces also had a significantly lower breaking strength. These experiments suggest that both as a competitor, and as potential prey, juvenile blue crabs have some disadvantages compared with these common sympatric exotic crab species, and in areas where these exotics are common, juvenile native blue crabs may be forced to expend more energy in conflict that could be spent foraging, and may be forced away from prime food items toward less optimum prey.