Comparison of the Feeding Rates of Two Introduced Crab Species, Carcinus Maenas and Hemigrapsus Sanguineus, on the Blue Mussel, Mytilus edulis

The European green crab, Carcinus maenas, and the Asian shore crab, Hemigrapsus sanguineus, are two introduced crab species that co-occur in the rocky intertidal zone of New England. Carcinus maenas has been established for over 100 years and has primarily been characterized as a molluscan predator, while H. sanguineus is new to the region and has an omnivorous diet. We compared the feeding rates of these two introduced crab species on the native blue mussel, Mytilus edulis, to determine their relative impacts on this important prey species. We utilized three size classes of mussels: small (4.5-5.5 mm shell length), medium (9.5-10.5 mm) and large (14.5-21.5 mm). Because feeding rates are expected to vary with biomass, we attempted to match the two crab species by weight rather than by carapace width. The two crab species had similar feeding rates on the smallest size class of mussel, while H. sanguineus had significantly higher feeding rates on the two larger mussel size classes. The higher feeding rate of Hemigrapsus sanguineus implies that it may have a larger per capita impact on prey populations than C. maenas did when it was established. The consequences of the increasing populations of H. sanguineus in northern New England are discussed.