Role of Chemical Inducers in Larval Metamorphosis of Queen Conch, Strombus gigas Linnaeus: Relationship to Other Marine Invertebrate Systems.

Chemical cues are important in the exogenous and endogenous control of metamorphosis in many marine invertebrate larvae. In the queen conch, Strombus gigas Linnaeus, larval metamorphosis is induced by low molecular weight compounds associated with dominant species of red algae found in conch nursery grounds; these species include the foliose rhodophyte Laurencia poitei (Lamouroux). The responses of conch larvae to the algal-associated cues are dependent on concentration and length of exposure, with the initial events of metamorphosis occurring within 10 min of treatment with an aqueous extract of L. poitei. The free amino acids valine and isoleutine mimic the effects of the natural inducer, and they may bind to and be recognized by the same sites on the larvae as the algal cues. Hydrogen peroxide, vanadate, and {gamma}-aminobutyric acid (GABA), as well as elevated K+ concentrations (i.e., above ambient seawater levels), also induce larval metamorphosis. Acetylsalicylic acid decreases the responses of conch larvae to the algal-associated cues and to the free amino acids, but it has no effect on the induction triggered by hydrogen peroxide. The chemical induction of metamorphosis in conch larvae shares many general features with chemoreception in aquatic invertebrates. The natural inducers of metamorphosis, like the cues involved in olfactory responses in other marine organisms, are of low molecular weight and water soluble. In addition, the results of the experiments with hydrogen peroxide, vanadate, and GABA suggest that second messenger pathways are involved in conch metamorphosis.