Long-term Effects of an Invasive Shore Crab on Cape Cod, Massachusetts

Invasive species can cause dramatic changes in the structure of intertidal communities. In some systems, however, abundance or impacts of invaders may peak 10-20 years after invasion and decline thereafter. Hemigrapsus sanguineus (Asian Shore Crab) has been established at Sandwich, MA, on the north side of Cape Cod, since the mid-1990s. This study documented population dynamics of the Asian Shore Crab and 3 species of prey or competitors (Carcinus maenas [Green Crab], Mytilus edulis [Blue Mussel], and Littorina littorea [Common Periwinkle]) over 10 years. An additional goal of the study was to determine whether population growth of the Asian Shore Crab has slowed since its initial establishment. Density of the Asian Shore Crab increased over time, with no evidence of a density-dependent decrease in per capita growth rates. Concurrently, density of the Green Crab and the Blue Mussel declined, but there was no significant temporal trend in density of the Common Periwinkle. If observations at Sandwich are representative of sites north of Cape Cod, populations of the Asian Shore Crab are growing rapidly, and dramatic changes in community structure may be widespread.