Invasive alien plants in marine protected areas: the Spartina anglica affair in the European Wadden Sea

Abstract

The common cord-grass Spartina anglica, a fertile hybrid of S. maritima and S. alterniflora, was planted in the European Wadden Sea extensively during the late 1920s and 1930s to promote sediment accretion. After establishment, it colonised as a pioneer plant in the upper tidal zone, where it occurs frequently in coherent swards at the seaward front of saltmarshes and in patches on the tidal flats. Often, a conspicuous, almost monotypic, belt of S. anglica is formed. Over the last two decades, an increase in abundance and accelerated spread of S. anglica was observed, possibly promoted by warmer spring temperatures. This alien species may benefit from global warming, and there is considerable concern about its harmful impacts on the native biocoenoses and native biodiversity of the unique Wadden Sea ecosystem, encompassing effects on hydromorphodynamics and coastal protection. For a definitive assessment, however, an adequate quantification and comparison of documented and potential effects of S. anglica is important, but currently unavailable. Consequently, no management strategy exists for the prevention or restoration of the Wadden Sea ecosystem. Thus, the development of an alien species plan on the level of the Trilateral Cooperation on the Protection of the Wadden Sea is essential.