In this focal theme we investigate trophic interactions. Besides consumptive effects of herbivores and predators also their non-consumptive effects on the morphology, chemical cues or the behavior of the prey are investigated. The mere presence of predators (e.g. crabs or predatory snails) may induce a series of responses: the prey may either be reluctant to settle in the habitat or be in frequent search of shelter and thereby reduce its own feeding activity. The developing trophic cascades can lead to shifts in the balance between species. An example is the stand-forming intertidal wrack Fucus serratus that indirectly profits from the presence of predators.