Nonnative macrobenthos in the Wadden Sea ecosystem

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t An inventory in the Dutch-German-Danish Wadden Sea revealed a total of 66 nonnative (alien) taxa including 17 tentative cryptogenics in the brackish-marine macrobenthos until 2010, which is close to average compared with similar inventories from other coasts. Although the Wadden Sea is known for the largest sedimentary tidal flats in the world, most aliens encountered were fouling at harbor walls, pontoons in marinas, at hard structures for coastal defense but also in epibenthic mussel and oyster beds. Recent qualitative rapid assessments focusing on port localities have substantially improved knowledge on introduced species in the Wadden Sea. Nonnative species have pervaded algal and invertebrate communities, and the guild of suspension feeders became particularly strengthened by aliens which took advantage of a recent phase with relatively warm years. Most alien species were not directly introduced into the Wadden Sea but have spread secondarily from adjacent coasts with more active harbors or shellfish cultures. We suggest that aliens which have already established in the Wadden Sea ecosystem should be tolerated to avoid ongoing manipulations in eco-evolutionary developments in this protected nature area. Mitigation of the advancing tide of invasive aliens should focus on vector control (shipping and open aquacultures) as well as on early detection with attempts of eradication during the initial phase of invasions on a scale of the entire European Atlantic coast of which the Wadden Sea ecosystem is an integral part. In the Wadden Sea, species richness of macrobenthic organisms is comparatively low because this shallow coastal region of the North Sea is young with respect to geological history and has been above sea level during glacial periods. When 7,500 years ago sea level rise slowed down, barrier islands, extensive sediment flats, salt marshes and estuaries did evolve in roughly the present position (Reise et al., 2010). During the last thousand years, most salt marshes have gradually been converted into arable land, small estuaries into freshwater streams, large estuaries into shipping canals, and many soft shores into artificial hard shores (Lotze et al., 2005). Still, this coastal region is characterized by the largest coherent tidal flats on earth, attracting huge flocks of …