Effect of alcohol extracts of demospongiae on growth of periphytic diatoms

Antifouling potentialities of alcohol extracts of demospongiae, collected o ff east coast of India, against four dominant marine fouling diatoms are re ported. Of the 20 combinations worked out (5 sponges x 4 diatoms) 16-intera ctions showed activity accounting to about 80%. Plakortis simplex, Azorica pfeifferae and Dercitopsis sp. showed 100% growth inhibition against all th e 4 fouling diatoms (Navicula subinflata, Navicula crucicula, Nitzschia sp. , Amphora sp.) tested, implying the presence of patent antifouling compound s whilst, other extracts showed species specificity in their action. Howeve r, the same cells exhibited normal growth, when transferred to extract free media, pointing towards non toxic way of action. The EC50, values varied w ith extracts and test organisms used and ranged from 14 mu g/ml (A. pfeiffe rae vs N. crucicula) to 583 mu g/ml (Dercitopsis sp. vs Amphora sp.). The a ctive extracts totally arrested the silicate uptake an diatoms, treated wit h EC100 values, in relation to control. The degree of silicate uptake impai rment varied with extracts and test organisms used. The results imply the p ossible potentialities of these extracts in controlling the microfoulers.