Roles of bacterial community composition in biofilms as a mediator for larval settlement of three marine invertebrates

Abstract

This study investigated (1) the effects of salinity and temperature on the bacterial community composition of developing biofilms, and (2) the responses of marine invertebrate larvae (the polychaete Hydroides elegans and the barnacles Balanus amphitrite and B. trigonus) to these biofilms during settlement (i.e. attachment to a surface and metamorphosis into juveniles). Biofilms developed in a 3 x 3 array of salinity and temperature treatments resulted in different bacterial community compositions (revealed by DGGE and T-RFLP), bacterial densities and total biomasses. Larval settlement of B. amphitrite and B. trigonus was induced by biofilms developed at high temperatures (23 and 30°C), but was unaffected (B. amphitrite) or inhibited (B. trigonus) by those developed at a low temperature (16°C). The settlement response of these barnacles did not correlate with the biomass or the bacterial density of the biofilms, but did coincide with the marked differences in bacterial community composition between the biofilms developed at different temperatures. In contrast, larval settlement of H. elegans differed slightly among biofilms developed in different salinities, but not among those developed at different temperatures. This settlement response was moderately correlated with bacterial density but had no apparent relationship with bacterial community composition of the biofilms. Our results implied that the community composition and cell density of bacteria in biofilms, which can vary with local environmental conditions, may allow larvae of the 2 barnacles and H. elegans, respectively, to distinguish between habitats with different environmental conditions.