Predation behaviour of Cancer irroratus and Carcinus maenas during conspecific and heterospecific challenges

Abstract

We investigated the predation behaviour of rock crab Cancer irroratus and green crab Carcinus maenas in laboratory experiments in autumn 2006 and spring 2007 during various conspe- cific and heterospecific challenges. The number of prey eaten by a focal crab during a given chal- lenge was recorded for both crab species using competition treatments (solitary crab, 2 conspecifics or 2 heterospecifics) crossed with 2 different prey densities (4 or 30 mussels) and 3 different temper- atures (5, 12 or 20°C). To validate laboratory results, complementary field experiments were carried out in aquaculture leases in Prince Edward Island, Canada, in 2007, during which crab stomach con- tents from identical competition treatments were studied and mussel socks were surveyed monthly for crab abundance. In the laboratory, predation rates of both crab species generally increased with temperature and mussel density, and were not affected by the presence of a heterospecific regardless of the season. During autumn 2006, the Temperature × Mussel density interaction influenced the pre- dation rate of rock crab while only temperature affected the predation rate of green crab. During spring 2007, the predation rate of green crab varied again according to temperature whereas the pre- dation rate of rock crab was affected by the Temperature × Mussel density × Competition interaction. In the field, blue mussels Mytilus edulis were the most abundant food item observed in stomach con- tents. The competition treatments did not affect the stomach contents. Both crab species displayed different abundance patterns and seemed to avoid each other on mussel socks. Overall, our results suggest that the 2 crab species can potentially coexist.