Marine invertebrates settle, attach, and/or metamorphose in response to signals from several sources, including seaweeds. In response to the aquaculture challenge of producing constant numbers of juveniles from cultured species, natural inducers have been screened for their ability to improve those processes. However, few chemical inducers of attachment of invertebrates have been identified, and even less of these were secondary metabolites. The goal of this work was to isolate the natural products responsible for induction activity using bioassay-guided fractionation of the organic extract of the brown seaweed Stypopodium zonale and the attachment of juveniles of the common brown mussel, Perna perna, as a model. The meroditerpene epitaondiol, identified by comparison of spectral data with the literature, promoted as much as 4.7 times more mussel attachment compared to controls at the natural concentration found in this alga (0.041% of the crude extract or 0.012% of algal dry weight). This is the first report showing that a seaweed produces terpenoid compounds as cues for invertebrate attachment, and future studies evaluating this action on settlement of mussels in the field are expected to improve aquaculture technology by increasing mussel spat production.