INHIBITORY AND FACILITATORY EFFECTS OF MICROBIAL FILMS ON SETTLEMENT OF BALANUS AMPHITRITE AMPHITRITE LARVAE

Larvae of the barnacle Balanus amphitrite amphitrite Darwin (Crustacea: Cirripedia) respond to microbial surface film cues at settlement (i.e. attachment and metamorphosis). The effects of films of varying ages on the settlement behaviour of B. amphitrite cyprids were examined in laboratory choice assays using substrata preconditioned in natural seawater for longer periods (up to 18 d) than previous studies. Furthermore, in this study only known numbers of cyprids (either 1 or 20 larvae) per film treatment were investigated, allowing assessment of possible behavioural interactions between larvae. Quantitative analyses of the multi-species films permitted objective comparisons between film age treatments. A general trend of a reversal of the effect of filming on cyprid settlement response - from inhibitory to facilitatory - was noted with increasing film age and isolated cyprids responded similarly to groups of 20 cyprids. Microbial abundance and overall biotic diversity were found to be markedly greater in 'older' films. The facilitation of cyprid settlement by 'older' films contrasts with previously published studies on B. amphitrite and may be explained either by the greater ages of films assayed in the present study or qualitative/quantitative differences in films between studies.