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

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Abstract
Specimens [136] of soft corals (Coelenterata, Alcyonacea) were tested for toxicity by exposing Gambusia affinis (Vertebrata, Pisces) to aqueous extract of coral macerate and assessing mortality. Corals [68] were examined in detail utilizing behavioral responses of fish and 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 narcotization 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 occurs significantly less frequently in this group than in those examined from the northern Great Barrier Reef in an earlier study.

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