Perspectives

The island of Sylt is famous for its spectacular beaches and sandy dunes. This attracts many tourists to a landscape highly vulnerable to disturbance. At the same time the beaches are wave-breakers against the North Sea and engineers try to keep this function by regularly replenishing sand that has been lost to the sea. Research on basic ecological processes takes a prominent position within this framework of contradictory interest. Together with partners including coastal engineering, natural protection, and beach tourism we plan to study the dynamic effects of physical forcing by wind and waves onto the sediment, the organisms, and the nutrient flow from the lower reaches of the beach up to terrestrial dunes.

The North Sea and the Wadden Sea biota are linked by complex exchange processes of drifting and swimming organisms. This affects the development of phytoplankton blooms and benthic stocks. Starting with studies on tidal and seasonal migrations of shrimp (Crangon crangon) we try to develop a combined model on hydrodynamics and population development including both the coastal North Sea and the Wadden Sea.

Mussel (Mytilus edulis) beds and seagrass (Zostera noltii) meadows constitute prominent epibenthic structures in the Wadden Sea. They are centres of biodiversity and biomass and strongly influence nutrient exchange. The effects of commercial mussel fishery and subtidal mussel cultures are studied in an ecosystem context. Mussel beds and seagrass meadows change the hydrodynamics at the water-sediment interface and may stabilise the sediments against erosion. The hypothesis is tested that biodiversity depends on the degree of fragmentation of seagrass meadows and mussel beds. Seagrasses continuously decreased during the past decades and the meadows in the northern Wadden Sea seem to be the only major ones left. This asks for an intensive search for the causes.

The sediments off Sylt are highly dynamic which makes them a key factor of benthic ecology. In turn, many organisms may affect sediment stability by facilitating sedimentation (e.g., mussel banks and seagrass meadows) or erosion (e.g., lugworms Arenicola marina). Prevailing erosion in the tidal creeks, along the seaward and wadden-sided coastline, and presumably also in the shallow offshore area demands for trend monitoring and causal analyses by an interdisciplinary group of biologists and geologists.

In the Sylt area, ecological studies date back for >100 years. These historical data have been a valuable basis for detection and interpretation of current long-term changes. In order to enable similar comparisons in the future we perform a number of basic studies with special emphasis on biodiversity. In addition, in close collaboration with Biologische Anstalt Helgoland a number of benthic and pelagic parameters are continuously monitored. This aims to find the causes of changes, model their consequences and predict the future direction of ecosystem development.

Comparative studies among different coastal zones are a valuable basis to interpret the results obtained in the Sylt area and to test their scope for spatial extrapolation. Functions of the ecosystem are often linked to specific characters of a few dominant species. Therefore, characters special to the temperate zones often only become evident when compared with polar or tropical zones. In addition, knowledge on basic ecosystem functions in other coastal areas helps to predict the consequences of world-wide dispersal of coastal organisms by human activity.