CHEMICAL DEFENSES IN ANTARCTIC SOFT CORALS - EVIDENCE FOR ANTIFOULINGCOMPOUNDS

Organic extracts from the antarctic soft corals Alcyonium paessleri Ma y and Gersemia antarctica Kukenthal exhibited antimicrobial and antifo ulant activity. A third antarctic soft coral, the stoloniferan Clavula ria frankliniana Roule, exhibited no such bioactivity. Marine bacteria l attachment was inhibited in the presence of chloroform and aqueous m ethanol extracts of A. paessleri and G, antarctica, but not in the pre sence of solvent controls. Similarly, inhibition of microbial growth i n three sympatric species of antarctic marine bacteria occurred in res ponse to aqueous methanol extracts of these two soft corals, but not t o the controls. Antifoulant activity of chloroform extracts of A. paes sleri and G. antarctica was detected in a month-long field assay measu ring inhibition of benthic diatom settlement. Observed invertebrate re cruitment rates were too low to allow an evaluation of antifoulant bio activity. Laboratory growth experiments, employing the antarctic diato m Navicula sp. and larvae of the antarctic sea urchin Sterechinus neum ayeri Meissner, confirmed the presence of growth-inhibiting metabolite s in the soft corals A. paessleri and G. antarctica. These results sug gest that both A. paessleri and G. antarctica, which do not appear to be fouled in the field, possess bioactive compounds with antifoulant a ctivity. In contrast, C. frankliniana, which is often heavily fouled, appears to lack antifouling compounds.