Chemical investigation of the Mediterranean gorgonian Paramuricea clavata resulted in the isolation of two new alkaloids, 2-bromo-N-methyltryptamine (1) and 3-bromo-N-methyltyramine (2), together with nine known compounds (3-10 and linderazulene). The bromoindole derivative 3 is reported herein for the first time from a natural source. The chemical structures of these compounds were assigned by spectroscopic analyses and comparison with literature values. The antifouling activity and toxicity of compounds 1-10 were assessed using three marine biofilm bacteria and the Microtox assay. In contrast to commercial antifoulants, bufotenine (5) and 1,3,7-trimethylisoguanine (10) showed significant antiadhesion activity against one bacterial strain while being nontoxic.