Three's a crowd: Space competition among three species of intertidal shore crabs in the genus Hemigrapsus

Hemigrapsus sanguineus is a small shore crab native to eastern Asia. In the past two decades, this species has established breeding populations on both sides of the North Atlantic. However, H. sanguineus has not become established in the eastern Pacific despite abundant shipping contact with Asian ports and suitable intertidal habitat. The experiments reported here investigate potential interactions between the invasive H. sanguineus and two congeners native to the west coast of the United States ( H. oregonensis and H. nudus). Specifically, we tested interspecific competition for shelter at both the juvenile and adult life stages. We found that H. sanguineus adults have a strong preference for shelter and are unaffected by the presence of other species. However, juvenile H. sanguineus were out-competed for shelter, and this limitation may be preventing H. sanguineus from establishing a population in areas with high levels of early life-stage competition. ► Adult Hemigrapsus sanguineus exhibited a strong preference for occupying shelter. ► Adult H. sanguineus usage was unaffected by other species of the same carapace size. ► Adult H. nudus used the shelter less when paired with same-sized male H. sanguineus. ► Juvenile H. sanguineus shelter usage decreased in the presence of other species.