EFFECTS OF SECONDARY METABOLITES AND CACO3 ON FEEDING BY SURGEONFISHES AND PARROTFISHES - WITHIN-PLANT COMPARISONS

Tropical seaweeds and 'plant-like' animals often contain both secondar y metabolites and high concentrations of minerals. Typically, secondar y metabolites are most concentrated in the tip of the organism and min erals in the base. We used within-individual variation in defenses in the alga Neomeris annulata to test the hypothesis that surgeonfishes a re deterred from feeding by calcium carbonate but not by chemical defe nses, whereas parrotfishes are deterred from feeding by chemical defen ses but not by calcium carbonate. Our results supported this hypothesi s. The parrotfish Scarus sordidus preferred to feed on an artificial f ood containing CaCO3 compared to control food, but preferred control f ood over food containing a sesquiterpene-rich organic extract of N. an nulata. Two species of parrotfishes fed primarily on the metabolite-po or, CaCO3-rich basal regions of N. annulata, whereas 2 species of surg eonfishes fed primarily on the metabolite-rich, CaCO3-poor tips. Varia tion in grazing location had important consequences for N. annulata. I ndividuals grazed on the tips grew in length more slowly than individu als grazed around the base. Individuals grazed on the lips were tempor arily rich in CaCO3; individuals grazed around the base were temporari ly rich in sesquiterpenes. These patterns were probably not a result o f induction of defenses, but rather a consequence of selective removal of CaCO3-poor and sesquiterpene-poor material respectively.