TROPHIC CUES INDUCE METAMORPHOSIS OF QUEEN CONCH LARVAE (STROMBUS-GIGAS LINNAEUS)

The planktotrophic larvae of the gastropod Strombus gigas Linnaeus are metamorphically competent for 6 days, at which time they must make contact with a benthic cue or lose the ability to metamorphose. In this laboratory study, larvae were exposed to potential metamorphic inducers from juvenile conch habitats. Conspecifics and dilute solutions of macroalgae did not trigger metamorphosis. However, Batophora oerstedi J. Agardh, a food source of juvenile conch induced the highest percentage of metamorphosis in veligers (mean = 62%, SD = 16). Other cues which induced metamorphosis were sediment (mean = 51 %, SD = 11), Thalassia testudinum Koenig seagrass blades (mean = 36 %, SD = 13), and Thalassia testudinum detritus mean = 29%, SD = 16). Further analyses of epiphytic, organic, and inorganic components of macrophytes and sediment indicated that the associated epiphytes were the primary components for inducing metamorphosis. When veligers were exposed to Thalassia testudinum detritus collected from 6 seagrass habitats encompassing a conch nursery ground near Lee Stocking Island, Bahamas, metamorphosis was statistically higher for detritus from four sites within the nursery than two sites outside the nursery periphery. This indicated that Thalassia testudinum detritus varied in composition and quality from one habitat to another and that conch larvae probably metamorphose in response to trophic cues found in their juvenile habitats. This adaptive behavior may be a mechanism to ensure that larvae are recruited into conch nurseries which offer good growth and survival to juvenile and adult stages.