Increasing intercontinental ship traffic and marine aquaculture are responsible for high numbers of exotic organisms in the south-eastern North Sea. Effects of exotic species on native communities are intensely investigated at the Wadden Sea Station Sylt.

Even though the impacts of invasive species are generally regarded to be negative, a lot of positive effects on native species were found. The Japanese Seaweed Sargassum muticum, for example, increases native diversity by providing an additional habitat which is used by a diverse assemblage of algae and invertebrates. Furthermore, native fish species such as snake pipefish Entelurus aquoreus and sea stickleback Spinachia spinachia find food and shelter within S. muticum beds and increasing numbers of these endangered fish species can be observed.