Megalopae of the invasive crab Hemigrapsus sanguineus metamorphose in response to marine biofilms from different potential habitats.
Habitat characteristics favoring settlement and metamorphosis of larvae can affect the distribution and abundance of benthic marine invertebrates. Less selective responses to habitat cues by settling larvae can lead to broader distributions of species and potentially successful introduction to new geographic locations. This study tested whether marine biofilms, which serve as habitat cues for many invertebrates, enhance settlement and metamorphosis (molting) of megalopae of the invasive Asian shore crab Hemigrapsus sanguineus. Biofilms were allowed to develop on plastic mesh netting deployed in coastal locations with abundant rocky substrate (adult habitat) and estuarine locations with few rocks. Molting rates of laboratory-reared megalopae maintained with biofilm-covered netting were determined. Controls consisted of mesh netting without field-derived biofilms and seawater without netting. Experiments were also conducted with megalopae of a native species of estuarine mud crab, Dyspanopeus sayi, for comparison of responses. Both species molted faster in response to field biofilms regardless of habitat of biofilm development, although the response to biofilms compared to netting without biofilms was stronger for H. sanguineus than D. sayi. The broad response of megalopae of both species to biofilms suggests that positive responses to biofilms and physical structure could be important for successful colonization of crab species in general.