Chemical Defences in Soft Corals (Coelenterata: Octocorallia) of the Great Barrier Reef: A Study of Comparative Toxicities

Abstract

We have tested 136 specimens of soft corals (Coelenterata. Alcyonacea) for toxicity by exposing Gambusia affinis (Vertebrata, Pisces) to aqueous extracts of coral macerate and assessing mortality. Sixty-eight corals were examined in detail utilizing behavioral responses of fish as well as mortality rates to establish relative toxicities among and within coral genera. The responses exhibited by the fish ranged from rapid mortality through slow mortality and varying levels of narcotisation to negligible effects. With respect to individual soft corals, the fish exhibited varying patterns of response through time, and were sorted into 9 distinct groups via multivariate computer analyses according to similarity of these behavioral patterns. Only 2 of the genera tested, Lemnalia and Sarcophyton, were restricted to the most toxic set of groups. A number of genera such as Lobophytum, Sinularia, Nephthea, and Cespitularia had representatives which spanned the entire spectrum of responses from highly toxic to non-toxic. The wide range of toxicity determined for the specimens examined and the fact that approximately 50 % of all specimens were toxic suggests that chemical defences against predation are common in the Alcyonacea of the central region of the Great Barrier Reef. Toxicity, however, occurs significantly less frequently in this group than in those examined from the northern Great Barrier Reef in an earlier study.