More than one hundred introduced alien species have established below high tide level in the trilateral Wadden Sea, while none of the residents was expelled in return. As a net result, species and biogenic habitat diversity have increased. This contrasts with the popular generalization that species introductions are a major threat to native biodiversity. We suggest, time is ripe to reconsider our attitude towards the impacts of alien species on the ecological web in the Wadden Sea. We discuss underlying reasons for the disparity with terrestrial habitats such as on barrier islands. We recommend acknowledging the high integrative capacity of the Wadden Sea ecosystem, appreciating gains in biodiversity and in adaptive abilities for adjusting to climate warming, accepting established immigrants as new residents, and overcoming the outdated dichotomy between pristine and novel nature.