BROAD-SPECTRUM EFFECTS OF SECONDARY METABOLITES FROM THE RED ALGA DELISEA-PULCHRA IN ANTIFOULING ASSAYS

In this study the antifouling activity was investigated of a series of chemically related, halogenated furanones isolated from Delisea pulchra (Greville) Montagne, a red alga which is rarely fouled in the field. The metabolites were tested in laboratory assays against representatives of the three major groups of fouling organisms, the barnacle Balanus amphitrite amphitirite Darwin, the macroalga Ulva lactuca Linnaeus and a marine bacterium (strain SW 8). Settlement of barnacle cyprid larvae was strongly inhibited, with an EC(50) of < 25 ng . ml(-1) (25 ppb) for some compounds. The settlement and growth of algal gametes was also strongly inhibited, in some cases at concentrations as low as 25 ng . cm(-2). Growth of the marine bacterium SW8 was inhibited more strongly than by the common antibiotic gentamicin. Overall, activity of the D. pulchra metabolites was comparable to that of the heavy metals and biocides currently used in antifouling paints. However, no single compound was most active in all tests and some metabolites effective against one organism showed little or no activity against the others. The high but variable level of activity of the D. pulchra metabolites, coupled with their small size, relative stability, and ability to be synthesized suggest their potential use as active ingredients in antifouling coatings.