Field experiments were performed to investigate whether the newly developed biotic habitat (mixed mussel reefs of blue mussels and pacific oysters in the Wadden Sea) affects the occurrence of associated key organisms and their ecological functions. We investigated the grazing activity of periwinkles Interactions between Littorina littorea and barnacles attached to Pacific oyster reefs in the northern Wadden Sea. Experiments were done in spring 2015 on oyster reefs near the island of Sylt (Wadden Sea, North Sea). We used in- and exclusion experiments in the field.