Induced phenotypic changes due to infochemicals present in the water column are common phenomena in the aquatic ecosystem. Such infochemicals have to be reliable for the receiver and can induce changes on several hierarchical levels of biological organization. We present a synthesis of results concerning the infochemical-based phenotypic changes within the marine ‘Red Tide’ dinoflagellate Alexandrium spp. and its sympatric copepod grazers. We show that chemical cues from copepods induce a response that is specific on several levels: 1) On the level of the grazer itself, i.e. its grazing impact, 2) on the level of the Alexandrium species receiving the infochemicals and 3) on the genotypic level. As specific as the infochemicals are the observed phenotypic changes in the respective species / genotype that comprise morphology and toxin production (Paralytic Shellfish Poisoning Toxins, PSTs). We further present metabolomic and transcriptomic changes within Alexandrium spp. that will give additional insight into trait changes uninvestigated so far and the regulation of the PST-content in this notorious Red Tide species.