Growth inhibition of fouling diatoms by antipatharian colonies

Growth inhibition of four dominant marine fouling diatoms by alcohol extrac ts of antipatharian colonies, collected off the east coast of India, are re ported here. Of the three antipatharian colonies tested one antipatharian i nhibited the growth of all the four fouling diatoms on glass surface, imply ing the presence of potent algal growth inhibitors whilst the other extract s were species specific in their action. The same cells exhibited normal gr owth, when transferred in extract free media, indicating a nontoxic mode of action. The effective concentration for 50% inhibition (EC50) ranged from 90 mug/ml (Nitzschia sp.) to 756 mug/ml (Amphora sp.). The EC50 values for N. subinflata and N. crucicula were 215 mug/ml and 108 mug/ml, respectively . The active extracts totally arrested the silicate uptake by diatoms treat ed with EC100 values, in relation to controls. The degree of silicate uptak e impairment varied with the test organisms. The results show the presence of antifouling agents in this group of organisms. This is the first report of antifouling properties of antipatharian colonies.