Growth inhibition of fouling diatoms by antipatharian colonies

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