In exploring a substratum, Balanus amphitrite amphitrite Darwin (Crustacea: Cirripedia) cyprids deposit 'footprints' of antennular secretion. The results of in vitro settlement assays suggest that in addition to serving as a temporary adhesive, the secretion acts as a pheromone, in that its presence induces the settlement of conspecific cyprids. This result is in accord with a previous study on Balanus balanoides (L.) (=Semibalanus balanoides). In settlement assays, the pheromone is likely to contribute to an observed positive linear relationship between settlement and cyprid density. The density effect should thus be an important consideration in the design of barnacle settlement assays. In the field, cyprid searching behaviour may render a surface more attractive to settlement by cypris larvae.

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Settlement, attachment, and metamorphosis of larvae of marine invertebrates is extremely variable in the laboratory and in nature. The relative contributions of genetic, ontogenetic and environmental effects to this variation are not well understood. We tested for genetic, maternal and ontogenetic effects on permanent attachment of cyprids of the barnacle Balanus amphitrite (Darwin). Larvae were assayed for attachment in response to a control treatment and 3 artificial inducers: 20-hydroxyecdysone (20-HE), 3-isobutyl-1-methylxanthine (IBMX), and phorbol 12,13-dibutyrate (PDB). We observed strong family effects on attachment in the control, 20-HE, and IBMX treatments, suggesting that attachment in response to these treatments is influenced by genetic or maternal factors. In addition, attachment responses were correlated, indicating that the same genetic or maternal factors may affect attachment in each treatment. Family effects on attachment in the control treatments decreased with cypris age, suggesting the loss of genetically-or maternallyinfluenced discriminatory behavior in older larvae. The mechanisms underlying genetic or maternal effects on attachment may act via the external receptors and signal-transduction pathways regulating larval responses. Alternatively, there may be variation in larval 'vigor' or the rate at which cyprids attain metamorphic competence.

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