The Effects of Seaweed Secondary Metabolites on Biofouling

Antifouling activity is one poorly investigated property of seaweed natural products. To determine, in the field, whether seaweeds contain chemicals able to influence the settlement of fouling organisms, crude organic extracts from Stypopodium zonale, Dictyota menstrualis (Phaeophyceae) and Laurencia obtusa (Rhodophyceae) were incorporated at natural volumetric concentrations, into hard stable gels that served as substrata for fouling in the experiments. Fouling organisms settled at a significantly higher rate on plates treated with S. zonale extracts than on control gels, while settlement was strongly inhibited on gels containing L. obtusa extracts. Fouling on gels treated with the D. menstrualis extract was not significantly different from the fouling found on control gels. The findings suggest that the broad antifouling properties of the crude extract of L. obtusa inhibit the settlement of fouling as well as hinder the development of settled fouling species, thereby reducing the richness of species. The results imply that L. obtusa possibly harbours powerful agents that can be explored for the development of antifouling technology.