The antifouling activity of a series of hexane, ethyl acetate, ethanol and aqueous extracts from 11 species of marine sessile organisms collected from the south-east coast of China was investigated. Settlement inhibition of cyprid larvae of the barnacle Balanus albicostatus was used to evaluate their antifouling efficacy. Screening of the 44 extracts showed antifouling activity in 90.9% of the hexane extracts followed by 90.9% of the ethyl acetate, 72.7% of the ethanol and 36.4% of the aqueous extracts. The hexane extracts of Tubularia mesembryanthemum, Notarcus leachii cirrosus and Styela canopus, the ethyl acetate extracts of Bugula neritina and N. leachii cirrosus, and the ethanol extracts of B. neritina and Anthopleura sp. were the most active in inhibiting the settlement of B. albicostatus, with EC50 values all below 50 μg/ml. At least one of the four extracts of each tested species exhibited antifouling activity, suggesting that all 11 marine sessile organisms contained antifouling substances and they may have evolved chemical defences against biofouling on their surfaces.
