Effect of predation by the invasive crab Hemigrapsus sanguineus on recruiting barnacles Semibalanus balanoides in western Long Island Sound, USA

Since its introduction fewer than 20 yr ago, the spread of the Asian shore crab Hemigrapsus sanguineus along the east coast of the US has been remarkable. By many accounts it is now the numerically dominant brachyuran in rocky intertidal sites in Long Island Sound. Evidence from several laboratory studies has suggested that H. sanguineus could have significant consequences for barnacle abundance and distribution. In this study we used field caging experiments to determine the effect of this invader on recruitment (sampled at weekly intervals) of the indigenous barnacle Semibalanus balanoides. We found that although H. sanguineus readily consumed settling cypris larvae and early post-settlement juveniles, crab predation did not have a negative impact on barnacle recruitment when predator density was low (15 crabs 0.25 m(-2)). We also found a measurable decrease in barnacle density at medium (45 crabs 0.25 m(-2)) and high (90 crabs 0.25 m(-2)) predator densities after the larval settlement period had ended, but this effect was short-lived. Based on available estimates of Asian shore crab abundance in Long Island Sound, we conclude that crab predation will not have a significant impact on the recruitment success of S. balanoides populations.