Stimulation of molting in megalopae of the Asian shore crab Hemigrapsus sanguineus: physical and chemical cues

Abstract

The Asian shore crab Hemigrapsus sanguineus is a recent invader and abundant mem- ber of rocky intertidal coastlines of the eastern USA. Understanding factors influencing the settlement and metamorphosis of its larvae is important for predict- ing colonization of the species. For many species of brachyuran crustaceans studied to date, chemical cues in the natural environment stimulate molting of megalopae, the final larval stage, to the first crab stage, whereas physical cues alone have little or no effect. However, physical structure can influence the abundance of juvenile and adult crabs. In this study, I tested whether physical/structural and chemical cues stimulate molting of H. sanguineus in the labo- ratory. Molting rates of megalopae exposed to exu- dates from adult crabs (H. sanguineus and the green crab Carcinus maenas) and different physical cues varying in structural complexity (rocks with or with- out biofilms, silt particles, nylon mesh used in aqua- culture) were monitored. Megalopae molted sooner to the first crab stage in the presence of exudates of both crab species, rocks with and without biofilms, and all nylon meshes tested regardless of the size of mesh openings. By separating the effects of chem- ical and physical cues, this study shows both to be important during settlement and metamorphosis of Asian shore crab megalopae, potentially contributing to its successful colonization of North Atlantic coast- lines.