Citation Information: Wim J. Wolff, Jan P. Bakker, Karsten Laursen, Karsten Reise, 2010. Wadden Sea Ecosystem No. 29. Common Wadden Sea Secretariat, Wilhelmshaven, Germany
Abstract: Along the North Sea shore, the largest coherent tidal flat area of the temperate world has evolved. Sediment supply from the sea has sufficiently balanced a slow sea-level rise in the last 8,000 years to maintain a coastal configuration of a seaward sandy barrier, extensive tidal flats and episodically flooded marshes. The Wadden Sea is unique in that it consists of vast (4,700 km2) bare sand and mud flats, emerging twice daily at low tide. Oceanic waters dominate river influence, and dynamic sandy shoals and dune islands provide a partial shelter against waves and winds of a rough sea. In the course of a year, the Wadden Sea is visited by an unparalleled 10-12 million birds for foraging and resting on their East Atlantic flyway. Food provision in the form of tidal flat fauna is 10-20 times higher than in adjacent deeper waters. When the tide is in, the flats serve as a rich nursery for shrimp and fish. The Wadden Sea constitutes a gigantic biological filter between land and sea. This filter is primarily composed (1) of extensive beds of molluscan suspension feeders which filter the local tidal volume about twice a month, (2) of sediment kept permeable by bioturbating lugworms, and (3) of marsh vegetation which functions as a filter during episodic storm surges when waters are loaded with re-suspended fine particles. An impressive number of about 10,000 species of plants, fungi and animals thrive in the Wadden Sea. After a long phase of overexploitation, protection measures have triggered spectacular recoveries in breeding birds and seals. Large-scale land claims have ceased and the Wadden Sea is today highly rated for its serene beauty. Global warming with an accelerating sea-level rise, however, may threaten the sandy barrier and the extent of the tidal flats.