It has long been suggested that marine sponges have evolved defensive mechanisms to control epibiosis i.e. colonization of body surfaces by other organisms. The main goal of this thesis research was to investigate the potential controls of epibiosis in the sponge Mycale adhaerens, and the focuses of this study were on: 1) how larval settlement of the polychaete Hydroides elegans and colonization of indigenous benthic bacteria could be controlled in the sponge; 2) the importance of epibiotic bacteria in controlling epibiosis in this sponge; and 3) the stability of associations between epibiotic bacteria and the sponge. Waterborne metabolites of the sponge exerted either a toxic or anti-settlement effect on larvae, indicating a possible direct control of M. adhaerens on larval settlement. On the other hand, 75% and 40% of epibiotic bacteria of the sponge were non-inductive and inhibitive to larval settlement, respectively, suggesting an indirect control of M. adhaerens on larval settlement through nurturing specific bacteria on the body surface. Moreover, microbial films developed under the influence of the sponge extracts became either inhibitive to larval settlement or toxic to larvae. The inhibition on larval settlement was likely due to the modulation of surface bacterial community mediated by the sponge metabolites. An indirect control on larval settlement was demonstrated. Substantial differences in composition of bacterial communities on hydrogels incorporated with the sponge extracts were observed, indicating modulation of the bacterial community due to sponge extract components. The absence of several TRFs relative to the controls suggested an inhibition of colonization by specific bacteria. Using culture-dependent techniques, half of the indigenous bacterial species isolated from the reference surface were susceptible to the sponge extract and 61% to the epibiotic bacterial extracts, suggesting possible direct and indirect controls of bacterial colonization by the sponge and epibiotic bacteria, ...