Experimental induction of larval metamorphosis by a naturally-produced halogenated compound (dibromomethane) in the invasive mollusc Crepidula fornicata (L.)

In many marine benthic invertebrates, the larval stage is the main vector of dispersal. Selective metamorphosis of larvae into an appropriate habitat is then essential to the survival of the benthic adult, with profound implications for population dynamics. Within this context, the identification of causal external factors triggering larval metamorphosis is of primary interest. In the widely invasive marine species Crepidula fornicata (L.), adult conditioned seawater is an effective inducer but the inducer has not yet been chemically characterized. In the present study, we experimentally tested the inductive ability of dibromomethane (DBM), a halogenated compound naturally-produced by red algae of the family Corallinaceae that co-occur with C. fornicata in the field. Through a series of three experiments, we demonstrated that DBM effectively induces metamorphosis of C. fornicata larvae, with a strong dose–response effect. Positive responses were observed for the four tested concentrations (5, 50, 500 and 5000 ppm), 5000 ppm being the most effective at inducing rapid metamorphosis. At this concentration, larvae became responsive at least five days before they became responsive to excess KCl, a chemical commonly used to test for competence in C. fornicata. Whether DBM could be an effective natural inducer would require further studies to quantify DBM and other halogenated compounds in the vicinity of C.fornicata beds, where they could influence larval behaviour even in the absence of other settlement cues.