With the increase in globalisation, the amount of non-native or alien species have also increased considerably. It is therefore important to know the impact these species have on native communities. The island of Sylt, located in the north-eastern part of the German Wadden Sea, is a popular tourist destination, as well as an important location for oyster and mussel aquaculture. The aim of my study is to better understand the impact of alien species in fouling communities and their associated epibiota in the region of the Wadden Sea. To fulfil this aim, I studied the epibiota associated with the two biogenic substrates, the native blue mussel Mytilus edulis and the alien tunicate Styela clava. I collected the samples from the marina of List on the island of Sylt, facing the Wadden Sea and, hence, being a critical site where non-native species might settle first. My results show similarities between the substrates with regards to species richness, diversity and evenness. The communities of the two substrates are similar with regards to the dominating species (the amphipod Crassicorophium sextonae) and distinguishing by the presence and abundance of certain organisms, such as juvenile blue mussels appearing in high abundances on M. edulis. Non-native species appeared on both biogenic substrates, without displaying a clear preference. Styela clava might not be a habitat builder like M. edulis, but on an individual scale, the introduced tunicate represents a highly complex microhabitat on par with the native blue mussel, sharing and providing resources in an anthropogenic habitat. Based on my results and existing literature, I believe that the tunicate does not pose a threat to the native assemblages of the Wadden Sea.