Antifouling agents against the benthic marine diatom,Navicula salinicola Homarine from the gorgoniansLeptogorgia virgulata andL. setacea and analogs.

At concentrations found in the gorgonian corals,Leptogorgia virgulata (L.) andL. setacea (L.), homarine (N-methyl-2-carboxypyridine) and water-soluble extracts from the gorgonians that contained homarine inhibited the growth of the potential fouling diatom.Navicula salinicola Hust., by 50-60%. Homarine comprised 0.3 and 0.25% of the fresh weight ofL. virgulata andL. setacea, respectively, and the water-soluble extracts comprised 4.0 and 3.0% of the fresh weight of the gorgonians, respectively. Three compounds structurally related to homarine including, in order of most to least active, nicotinic acid, picolinic acid, and pyridine, also reduced growth ofN. salinicola. The activity of these compounds in the diatom assay suggests that the carboxyl group at the 2 position of the pyridine ring is important for activity and thatN-methylation is not important. We conclude that chemical defense against fouling is operative inLeptogorgia species. Evidence from the literature for combined chemical and mechanical defenses byLeptogorgia and other organisms against fouling is presented.