Marine Chemical Ecology

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Assessing the Chemical Defenses of Caribbean Sponges

Sponges are important components of benthic marine communities, particularly coral reefs. Organic extracts of their tissues have yielded a wealth of unusual chemical compounds that are not involved in primary metabolism, and have no known biological functions. The most commonly held theory is that these compounds are distasteful to potential predators, but they may also protect sponges from fouling or overgrowth. This research program, funded by the National Science Foundation’s Biological Oceanography program, is designed to assess the defenses of Caribbean demosponges, a group whose taxonomy and chemistry is fairly well described. Because reef sponges are abundant, sessile, elaborate putative structural and chemical defenses, and are subject to grazing from generalist and specialist predators, they provide a useful group for testing fundamental hypotheses proposed by terrestrial ecologists about plant defensive mechanisms.

Results to-date: In the first few years of this research program, the chemical, structural and nutritional antipredatory defenses of over 70 species of Caribbean sponges were surveyed using a laboratory feeding assay; the result is one of the most complete studies of the chemical and
structural defenses of a group of organisms from one biogeographic region. Subsequent field feeding experiments using a natural population of reef fish have supported lab assay results, and led to the isolation and identification of the deterrent compounds from several sponge species.
Both laboratory and field experiments have revealed that sponge structural elements, including glass spicules, do not appear to provide an antipredatory defense. A series of experiments in which sponges have been transplanted, caged, and exposed by overturning rubble, have clearly demonstrated that spongivorous fishes limit sponge distributions, and that parrotfish are major spongivores. These results have called into question conventional ideas about the effects of sponge-eating fishes on reef sponge communities.

Publications in Marine Chemical Ecology