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.