The project aims to follow the development of subtidal areas that were formerly used as mussel culture plots in the Sylt-Rømø Bight. Special focus is what effect the termination of fishing in these areas has on the mussel population and whether there are positive effects on other macroinvertebrate species associated to biogenic reefs.
The blue mussel (Mytilus edulis) is an important component of the Wadden Sea ecosystem. It facilitates benthic-pelagic coupling, influences sediment processes, provides structure to many other organisms, and thereby increases marine biodiversity. Besides its ecological importance, the mussel has also a high economic value and is one of the most important species for fisheries in the Wadden Sea. Aquaculture activities focus on the cultivation of seed mussels on bottom culture plots. The seed mussels are about 2–3 cm in shell length and are collected by fishing on subtidal wild mussel seed beds or originate from Seed Mussel Collectors. The mussel seed is relayed on the culture plots and cultured until a commercial size of about 4–5 cm is reached. During the culture process the plots are regularly fished to minimize epigrowth and reduce the abundance of a voracious predator, the common starfish.
In the Sylt-Rømø Bight, subtidal mussel culture plots once widely occurred throughout the entire area, but decreased considerably over the last decades. From 2017 onwards, the remaining culture plots were closed and all fishing activities on these plots were no longer allowed.
Since the areas used for mussel cultivation show a relative high mussel survival and growth, they may also serve as suitable areas for a natural development of subtidal mussel beds. As such, these areas may provide valuable information and may help to fill knowledge gaps on the ecology and macrobenthic community of undisturbed subtidal mussel beds.