Chemical inhibition of epibiota by Australian seaweeds

Abstract

Detailed, ecologically realistic studies of chemical inhibition of fouling (epibiosis) by marine organisms are rare. A first step in understanding chemical mediation of the interaction between epibionts and their hosts is to quantify potential inhibitory molecules on or near the surface of an alga (or other organisms) in the field. In situ quantification can be difficult, and measurements will be affected by the polarity of the molecules, hydrodynamics, ultrastructure of the producing organism, and the specific chemical structure of the molecules. All these factors also influence the effects of the compounds on epibiota. Here, some approaches are described to address these issues, emphasizing the need for ecological realism in measuring active ingredients, testing against ecologically relevant epibiota, and conducting, whenever possible, experiments and measurements in the field. Evidence to date indicates that active natural inhibitors of colonization are mostly non‐polar metabolites. However, not all non‐polar metabolites appear to be effective at inhibiting epibiota, either because the compounds are not presented at or near the surface of the host organisms in an appropriate way, or because they have low activity against relevant fouling organisms. This variation in the activity of different non‐polar metabolites appears to be primarily due to differences in their effect as chemicals per se rather than differences in their physicochemical properties, although in most instances the specific physiological mechanisms by which metabolites inhibit fouling organisms are not known. However, for halogenated furanones from Delisea pulchra, current research suggests that these metabolites inhibit bacterial colonization of the host alga by interfering with a class of bacterial genetic regulatory pathways known as AHL (acylated homoserine lactone) regulatory systems.