Multiple Defensive Roles for Bromopyrrole Alkaloids from Caribbean Agelas Sponges

Previous studies have indicated that Caribbean reef sponges of the common genus Agelas are chemically defended from fish predators by brominated pyrrole alkaloids: Agelas clathrodes and A. wiedenmayeri by 4,5-dibromopyrrole-2-carboxylic acid (1) and oroidin (2), A. conifera by sceptrin (3). In this study, we expand our understanding of chemical defense in this sponge genus to include an extensive HPLC quantification analysis of the defensive metabolites in tissues of A. cerebrum, A. cervicornis, A. dilatata, A. dispar and A. sceptrum. A. cervicornis and A. dispar contained the same two major metabolites as A. clathrodes and A. wiedenmayeri, while A. cerebrum, A. dilatata and A. sceptrum contained a mixture of dimeric bromopyrrole alkaloids dominated by sceptrin, similar to A. conifera. At natural volumetric concentrations, both crude extracts and purified compounds from each species were unpalatable to a common generalist reef fish, Thalassoma bifasciatum, in aquarium assays, and inhibited attachment of the marine bacterium Vibrio harveyi in surface fouling assays. Brominated pyrrole alkaloids may play multiple ecological roles in protecting sponges of the genus Agelas.