A highly specific chemical cue for the metamorphosis of the Asian shore crab, Hemigrapsus sanguineus

Hemigrapsus sanguineus (Brachyura: Varunidae) has become an important part of rocky intertidal habitats in the Western Atlantic Ocean since its translocation and invasion in the late 1980s. While much of the focus on this crab has involved direct prey/predation relationships between H. sanguineus and native flora and fauna, less is known about the early life stages. The goal of the experiments presented here was to evaluate the chemical cues that stimulate H. sanguineus post-larvae (megalopae) to metamorphose. Previous studies indicate that a cue found in the exudate from conspecific adults induces metamorphosis in H. sanguineus megalopae. Here we report the results of H. sanguineus megalopae exposed to exudates produced by closely related species (Hemigrapsus oregonensis, Hemigrapsus nudus, Hemigrapsus penicillatus, and Hemigrapsus takanoi), as well as exudates produced by several other brachyuran crabs and one anomuran crab. We also investigated chemical characteristics of the metamorphic cue, including thermal stability and molecular size. Our results indicate that the metamorphic response is highly species-specific, and H. sanguineus megalopae only respond to conspecific exudates. This exudate is stable after freezing, but loses some potency after exposure to boiling temperatures. The active molecule is between 3.5 and 14 kDa in size.