The Asian shore crab, Hemigrapsus sanguineus (De Haan, 1853), is an opportunistic omnivore with well-developed predatory tendencies and a strong preference for animal food items over algae. In laboratory experiments, 71 percent (319/448) of the crabs given a choice between macroalgae (Enteromorpha spp. and/or Chondrus crispus) and benthic invertebrates (Mytilus edulis and/or Semibalanus balanoides) consumed animals only. There were no significant differences in food preference between sexes or between juvenile and adult crabs. Relative abundance of food type, either algal or animal, in small food patches did not affect crab food preference. Crabs with prolonged starvation periods (5-d), however, consumed both food types more often than those that had been starved for 1-d only. Experiments to determine the effect of conspecifics on food selectivity showed that increased crab density leads to increased diet breadth, suggesting that competition for food can alter food selection patterns of H. sanguineus. Results reported here and in previous studies provide strong evidence that predation pressure exerted by H. sanguineus could play an important role in structuring the post-settlement population dynamics of its invertebrate prey, possibly leading to population declines of commercial shellfish, especially blue mussels.