Premium
Calcium Carbonate and Secondary Metabolites in Tropical Seaweeds: Variable Effects on Herbivorous Fishes
Author(s) -
Schupp Peter J.,
Paul Valerie J.
Publication year - 1994
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1939440
Subject(s) - aragonite , calcium carbonate , biology , herbivore , halimeda , ecology , coral , chemistry , organic chemistry
On coral reefs where herbivorous fishes are both numerous and diverse, many seaweeds combine mineral and chemical defenses. We hypothesized that combined defenses affect a greater number of herbivore species than either single defense, and in this study we experimentally tested this hypothesis. We first incorporated calcium carbonate (aragonite form) alone at a range of concentrations into an artificial diet composed of freeze—dried samples of the noncalcified, green alga Enteromorpha calathrata, carragenan, cornstarch, and water. In field experiments where diets were made available to a natural fish community, aragonite had variable effects: in some trials aragonite deterred feeding, in others it had no significant effect, and in one trial it even simulated feeding. Parrotfishes (Scaridae) and the surgeonfish Ctenochaetus striatus (Acanthuridae) showed a significant preference for food containing aragonite in field observations, while the surgeonfish Naso vlaminigii and three damselfishes (Pomacentridae) were observed to feed preferentially on food without added aragonite. In the laboratory, the surgeonfishes Acanthurus nigrofuscus, A. triostegus, A. xanthopterus, and Naso unicornis and the rabbitfish Siganus spinus (Siganidae) significantly avoided food with added aragonite. However, the parrotfishes Scarus sordidus and S. schlegeli consumed significantly more food containing aragonite the plain food. Ctenochaetus stiatus avoided aragonite only at the highest aragonite concentration and showed no preference at lower aragonite concentrations. Artificial diets containing natural concentrations of aragonite (80% dry mass), dieter—penoid secondary metabolites from Halimeda macroloba (1% dry mass), and a combination of both defenses (80% aragonite and 1% aragonite—free dry mass of diterpenes) were tested in the laboratory against four fish species. Scarus sordidus and Ctenochaetus striatus avoided secondary metabolites but not aragonite, and Naso lituratus and Signaus spinus were deterred by aragonite but not by secondary metabolites. All fishes were deterred by one defense or the other, and all fishes but Scarus sordidus avoided food containing the combined defenses. Combinations of aragonite and secondary metabolites increased the number of fish species that were effectively deterred from grazing relative to either single defense.