Unique natural products produced by many species of tropical marine algae have been implicated in chemical defense against herbivores. In this field study, extracts from seven common seaweeds from Guam and four chemically pure secondary metabolites from tropical algae were tested for
their ability to deter herbivorous fishes. Several species of preferred algae including Acanthophora specifera, Enteromorpha clathrata, and Sargassum polycystum were coated with these extracts or purified metabolites at approximately natural concentrations and offered to herbivorous
fishes with adjacent solvent controls. The experiments were performed in reef habitats with large populations of herbivorous fishes, and therefore test the ability of these algal natural products to deter natural populations of herbivores. Two extracts and four natural products significantly
reduced grazing by herbivorous fishes. Most of these natural products were isolated from algae that are resistant to grazing by herbivores. Previous results of laboratory assays examining the biological properties of these natural products did not accurately predict the deterrent effects of
the compounds in these field assays. Results of these experiments differed when the assays were performed in different reef habitats. These results suggest that different responses to the chemical defenses of some tropical algae occur among different herbivorous species and among habitats.
The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.