Mechanisms for the range expansion of the invasive shore crab Hemigrapsus sanguineus

Hemigrapsus sanguineus is an invasive shore crab in the rocky intertidal habitats of the Atlantic basin. Native to the western Pacific, it has established populations in North America from Maine to North Carolina and in coastal France. The crab has spread rapidly since its initial discovery in 1988 in Delaware Bay and it has the potential to continue its range expansion. The species has become an ecological and economic threat in its new habitat; however, little is known about its method of range expansion. This research examines the mechanisms of spread of H. sanguineus by investigating the potential for both larval and anthropogenic transport. I have found evidence that the larvae are capable of long-distance transport. Larvae are released on nocturnal ebb tides and are rapidly exported from estuaries to develop in the coastal ocean. Depending on conditions, total larval duration extends from one to more than two months. Zoeal development appears to occur on the continental shelf and larvae may be transported considerable distances both north and south by prevailing coastal currents. Larvae may return to adult habitat by migrating to bottom waters where subtidal flow is landward. After returning to the rocky intertidal, the juveniles and adults have high survivorship, allowing for the dense populations seen in the invaded habitats. While the likelihood of anthropogenic re-introductions was not resolved in the current study, it seems likely that human-mediated movement may also contribute to the rapid spread of this species. I conclude that H. sanguineus has the capacity for long-distance larval transport and that this transport has promoted the rapid range expansion of this species. Because of this ability for long-distance transport, I predict a continued spread of H. sanguineus to rocky intertidal habitats in the North Atlantic and beyond.