Presently, studies on inducible anti-herbivory responses in seaweeds focused on grazer-mediated changes in algal palatability of subsequent consumption by conspecifics. Yet, in natural systems multiple species interact, suggesting the existence of more complex, indirect interactions. Feeding-assayed induction experiments in the laboratory were conducted to test for direct and indirect induction of anti-herbivory resistance in the brown seaweed Fucus vesiculosus. For induction, algae were exposed for 14 d to either the isopod Idotea baltica or the periwinkle Littorina littorea. For testing effects of induced resistance, fresh and reconstituted Fucus feed were offered in 3 d long feeding assays to conspecific and non-conspecific herbivores. The experiment was simultaneously executed with organisms shared by the North and Baltic Sea to test for system-spanning patterns. Experiments revealed direct induction effects. Idotea-grazing reduced the palatability of Fucus-pieces from the North Sea for naοve conspecifics, but not in Fucus from the Baltic Sea. Grazing by Littorina also lowered the level of palatability in Fucus-pieces for naοve conspecifics, but only in algae from the Baltic and not from the North Sea. Moreover, indirect effects were observed. Idotea-exposed Fucus did not influence algal palatability for subsequently grazing periwinkles at both sites, while Littorina-exposed Fucus from both sites was significantly less consumed by Idotea. Palatability patterns in assays using reconstituted food matched with those using fresh Fucus-pieces, suggesting an induction of chemical anti-herbivory defences in Fucus. Furthermore, the observation of detrimental Littorina effects on Idotea-consumption at both sites suggests a system-spanning grazer-specificity of indirect. This study shows that indirect effects may commonly affect trophic interactions in and thus add a novel level of complexity to the development of macrophytobenthic communities.