Chemically mediated antifouling in the red alga Delisea pulchra

Using laboratory assays, we tested whether the secondary metabolites (furanones) on the surface of the red alga Delisea pulchra deter the settlement and growth of a range of ecologically relevant fouling organisms. D. pulchra and 4 other co-occurring seaweeds were almost exclusively fouled by other algae. Consequently, we carried out laboratory assays using propagules from 4 fouling algae (Ulva sp., Ceramium sp., Polysiphonia sp. and Ectocarpus siliculosis) representing the natural fouling community. The crude surface extract of D. pulchra at the same concentration as on the surface of the plant, the furanone fraction of this extract, and pure furnaones, deterred the settlement of fouling organisms in ecologically relevant assays. These data, coupled with knowledge of the surface concentration of furanones on D. pulchra and a mechanism by which furanones are sequestered onto the surface of the plant, provide a rigorous demonstration of chemically mediated antifouling.