In this study, we screened seven novel sponge-associated marine bacteria for their antibacterial and antilarval-settlement activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-bacterial-growth activity of crude extracts of each bacterium was evaluated by the disk-diffusion assay. Extracts of four potent bacteria with high and broad spectra of antibacterial activity were further separated with solvents of different polarities (hexane and ethyl acetate). To evaluate their indirect inhibitive effect on larval settlement, we tested for their antibiofilm formation activity against two of the test bacteria (Vibrio halioticoli and Loktanella hongkongensis) inductive to Hydroides elegans larval settlement. About 60 and 87% of the extracts inhibited biofilm formation by V. halioticoli and by L. hongkongensis respectively. The extracts were also tested for their direct antilarval-settlement activity against the barnacle Balanus amphitrite and the polychaete H. elegans; 87% of the extracts had a strong inhibitive effect on larval settlement of both species. Extracts of two of the isolates completely inhibited larval settlement of B. amphitrite at 70 microg ml(-1) and H. elegans at 60 microg ml(-1). The organic extracts of Winogradskyella poriferorum effectively inhibited the larval settlement of both H. elegans and B. amphitrite and the biofilm formation of the two bacterial species. The metabolites present in the active crude extracts were profiled using GC MS, and the most prevalent metabolites present in all extracts were identified. This study successfully identified potential new sources of antifouling compounds.