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.

Associations between macrobenthos and invasive cordgrass, Spartina anglica, in the Danish Wadden Sea

“…The Wadden Sea is treasured by its special native biodiversity and is a stepping stone for a variety of migratory waterbirds (Vinther et al 2001;Loebl et al 2006). S. anglica was introduced in the Danish Wadden Sea around 1,940 where no native Spartina species were present (Nehring and Hesse 2008). Since then, meadows and scattered tussocks of S. anglica have been common features in many intertidal parts of the Danish Wadden Sea.…”

“…Since then, meadows and scattered tussocks of S. anglica have been common features in many intertidal parts of the Danish Wadden Sea. The ecological consequences of this robust halophyte invasion remain largely unexplored in this area (Nehring and Hesse 2008).…”

“…Provided the signiWcant roles and feasibility for experimental analysis, macrofauna assemblages are generally regarded as important indicators of system resilience to disturbances, such as biological invasions, pollution and eutrophication (Snelgrove 1998;Levin and Talley 2000). The accelerating concerns on bioinvasions in coastal soft-sediments have inspired much recent research (Reise et al 1999Thieltges et al 2006;Cottet et al 2007;Nehring and Hesse 2008).…”

The Dynamics of Plant-Mediated Sediment Oxygenation in Spartina anglica Rhizospheres—a Planar Optode Study

“…anglica thrives in low marshes in a wide variety of substrates, including clays, fine silts, organic muds, sands and shingle, and is tolerant to regular tidal inundations with oceanic salinity (Gray and Marshall, A. Raybould 1991). S. anglica colonizes frequently inundated bare mudflats and competitively excludes native wetland species in low marshes (Nehring and Hesse 2008). S. anglica is successfully spreading in many wetlands and coastlines around the world from New Zealand to the North American west coast and is in many places considered an invading species (Nehring and H. Adsersen 2006;Nehring and Hesse 2008).…”

“…S. anglica colonizes frequently inundated bare mudflats and competitively excludes native wetland species in low marshes (Nehring and Hesse 2008). S. anglica is successfully spreading in many wetlands and coastlines around the world from New Zealand to the North American west coast and is in many places considered an invading species (Nehring and H. Adsersen 2006;Nehring and Hesse 2008). The high oxygen transport capacity of S. anglica is considered an important factor for its ability to inhabit bare mudflats and to outcompete native species in the low marsh (Maricle and Lee 2007).…”