Microbial films, which develop on submerged artificial surfaces, elicit variable responses in settling invertebrate larvae. There is no information on the response of the larvae of the tropical fouling barnacle, Balanus reticulatus to biofilms. Therefore, the influence of biofilms and their components (such as bacteria, diatoms and bacterial exopolymer) on settlement of cyprid larvae of B. reticulatus has been studied. Biofilms significantly reduced larval settlement when compared to clean polystyrene surfaces (control). No significant correlation was found between percentage settlement and biofilm age. Inhibition or induction of settlement was observed, depending on the cell density and growth phase of the bacterial films. Diatom films, regardless of cell density, were inhibitory to cypris settlement. Bacterial exopolymers did not influence settlement at low concentrations (0.001 to 0.0001 %), but inhibited settlement at higher concentrations (0.1 to 0.01%). Our study indicates that presence of natural biofilms and their components such as bacteria, diatoms and bacterial exopolymers on polystyrene render an otherwise attractive surface unsuitable for settlement by larvae of B. reticulatus
