Effect of alcohol extracts of demospongiae on growth of periphytic diatoms

Abstract

Antifouling potentialities of alcohol extracts of demospongiae, collected off east coast of India, against four dominant marine fouling diatoms are reported. Of the 20 combinations worked out (5 sponges x 4 diatoms) 16-interactions showed activity accounting to about 80%. Plakortis simplex, Azorica pfeifferae and Dercitopsis sp. showed 100% growth inhibition against all the 4 fouling diatoms (Navicula subinflata, Navicula crucicula, Nitzschia sp., Amphora sp.) tested, implying the presence of patent antifouling compounds whilst, other extracts showed species specificity in their action. However, the same cells exhibited normal growth, when transferred to extract free media, pointing towards non toxic way of action. The EC50, values varied with extracts and test organisms used and ranged from 14 mu g/ml (A. pfeifferae vs N. crucicula) to 583 mu g/ml (Dercitopsis sp. vs Amphora sp.). The active extracts totally arrested the silicate uptake an diatoms, treated with EC100 values, in relation to control. The degree of silicate uptake impairment varied with extracts and test organisms used. The results imply the possible potentialities of these extracts in controlling the microfoulers.