Induction of metamorphosis in queen conch, Strombus gigas Linnaeus, larvae by cues associated with red algae from their nursery grounds

Abstract

Strombus gigas Linnaeus larvae are induced to metamorphose by a selection of substrata from their nursery grounds. The most effective inducers are cues associated with red algae, specifically Laurencia poitei (Lamouroux) Howe and the epiphyte Fosliella sp. (Foslie) found on Thalassia testudinum Köenig detritus. Larvae metamorphose in response to these intact rhodophytes and to aqueous extracts of these species. The cues associated with Laurencia poitei and Fosliella sp. are water soluble and of low molecular size (<1 kDa). They are stable over time (≈ 12 months) and their activity is not altered by heat treatment (10 min of boiling). Although the larvae respond to aqueous extracts of the red algae, their response in the presence of whole plants appears to be contact or near surface dependent. Unlike many invertebrate larvae that are induced to metamorphose by red algal species, Strombus gigas do not respond to the neurotransmitter γ-aminobutyric acid (GABA). The responses of the larvae to the various nursery ground substrata and to cues isolated from their extracts is discussed in relation to temporal and spatial variability in the suitability of seagrass beds as sites for conch metamorphosis.