Biogeographic comparisons of chemical and structural defenses of the Pacific gorgonians Annella mollis and A-reticulata

Compared to other areas of chemical ecology, biogeographic comparisons of the chemical defenses associated with benthic marine organisms are few. This study addresses geographic differences in the chemical and structural defenses of 2 Pacific gorgonians (Annella mollis and A. reticulata), found at 2 islands: Guam, Micronesia, and Lizard Island, Australia. Crude extracts and sclerites extracted from the mid-axis and tips of colonies were assayed against natural assemblages of reef fishes at Western Shoals, Guam, and Mermaid's Cove, Lizard Island. Reciprocal feeding assays clearly demonstrated that crude extracts from Annella spp, were unpalatable to natural assemblages of reef fishes at Western Shoals and Mermaid's Cove and sclerites have little or no role as generalist predator defenses. Sclerites from the tips of A. reticulata were only effective as feeding deterrents at high concentrations. Variation in the palatability of the mid-axis extracts of A. mollis suggested that chemical defenses are more concentrated at the tips of the colonies from Guam and Lizard Island. When assayed at concentrations similar to and higher than the tips the mid-axis extracts did not deter fish feeding at Mermaid's Cove.