Antifouling activities of octocorals on some marine microfoulers

The antifouling activities of vacuum-dried 70% aqueous alcohol extracts of four gorgonian and five soft corals against four dominant marine fouling di atoms (Navicula subinflata Grun, N. crucicula Smith, Amphora so., Nitzschia sp.) are described. Of the 36 possible combinations (9 corals x 4 diatoms) 23 of the interactions (64%) showed 100% activity. Extracts of the gorgoni an coral Echinogorgia complexa Nutting and the soft coral Dendronephthya (M orchellana) sp. showed 100% growth inhibition against ail four fouling diat oms, implying the presence of potent broad spectrum antifouling compounds; other extracts showed more limited species specificity. Exposed cells when transferred to extract-free media, resumed normal growth indicating a nonto xic way of action. The effective concentration for 50% growth inhibition of the attached cells (ECS,) varied for each extract and test organism used. The EC50 values for the extract of the gorgonian coral E. complexa against the fouling diatoms ranged from 86 mug/ml (N. subinflata) to 505 mug/ml (Am phora sp.) whereas the EC50 values for extracts of the soft coral Dendronep hthya (Morchellana) sp. varied from 28 mug/ml (N. crucicula) to 415 mug/ml (Amphora sp.). The results support the hypothesis that octocorals contain a ntifouling agents, which could be exploited for the development of nontoxic natural antifouling technology.