The introduction of non-indigenous species may cause strong effects on biodiversity, species interactions and functioning of native soft-bottom coastal ecosystems. Especially introduced bioengineering organisms modify existing benthic habitat structures and thereby habitat-specific species interactions. In the Wadden Sea, beds of native blue mussels have been invaded by Pacific oysters Magalana gigas, which caused a large-scale shift from pure epibenthic Mytilus edulis beds to current mixed reefs of mussels and oysters. These newly developed biotic habitats may affect the occurrence of former associated key organisms and their ecological functions. In this context, we studied the grazing activity of native periwinkles Littorina littorea and the spatial distribution of M. edulis in oyster reefs in the northern Wadden Sea and explored the resulting distribution patterns of barnacle epibionts attached to oyster and mussel shells. A manipulative field experiment revealed that density of L. littorea significantly affects the recruitment success of barnacles Semibalanus balanoides on oyster shells. The highest number of barnacles recruited at periwinkle exclusion and this relationship was already known for pure blue mussel beds in the past. Barnacle epigrowth on blue mussel shells, however, changed with the new position of mussels within the oyster matrix and is nowadays lower than in former times. Our results demonstrate that introduced bioengineering organisms may alter, native biotic habitats but associated species interactions may remain the same. Additionally, it shows that native species may profit from the new structures by, for example, being less overgrown with detrimental barnacle overgrowth.