DEFENSIVE STRATEGIES OF SOFT CORALS (COELENTERATA: OCTOCORALLIA) OF THE GREAT BARRIER REEF. II. THE RELATIONSHIP BETWEEN TOXICITY AND FEEDING DETERRENCE

¹ Department of Chemistry and Biochemistry, James Cook University of North Queensland, Townsville, Qld, 4811, Australia
² Australian Institute of Marine Science, P.M.B. No. 3, M.S.O., Townsville, Queensland, 4810, Australia

Thirty-six specimens of soft corals (Coelenterata, Alcyonacea) were tested for toxicity by exposing Gambusia affinis (Vertebrata, Pisces) to aqueous extracts of coral macerate and assessing mortality. Fifty percent of the soft coral extracts were determined to be ichthyotoxic to the fish, supporting earlier studies. In another experiment, commercial fish food was immersed in the same aqueous soft coral extracts, dried, and offered to G. affinis at three concentrations with appropriate controls. The study of feeding deterrence showed that 88% of the 36 extracts produced negative feeding responses at the highest concentration. At intermediate concentrations, 75% of the extracts acted as feeding deterrents; 48% showed detectable deterrence at lowest concentrations. Levels of toxicity and feeding deterrence, however, were not correlated; i.e., feeding deterrence was as common among non-toxic corals as among toxic ones. This finding may help to explain why some soft corals, which apparently lack toxic defense substances, do not exhibit signs of predation in the field.

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