Improving the definition of a coastal habitat: Putting the salt back into saltmarsh

Definitions of saltmarsh vary, with approaches based on the European Union Water Framework Directive (WFD) and the Habitats Directive differing from major definitions in the literature, and from each other, giving rise to confusion and differing approaches to calculations of extent. Habitats Directive definitions also differ across Europe. This paper's main aim is to derive a detailed definition of the saltmarsh habitat that satisfies the ecological principles of saltmarsh as defined in the literature. This is then related to the Directives by examining each Directive in the context of phytosociology and UK and European Ellenberg Numbers for Salinity. A definition is offered that is precise in vegetational terms and complies with most literature definitions, notably in respect of the importance of halophytes. Although our method has been applied to the UK National Vegetation Classification, the technique can be extended to any vegetation type for which a salt tolerance index is available. Conflation of saltmarsh definition and conservation is reviewed and removed in a way that retains the ability to protect the habitat in its wider context. It is essential that all accounts of saltmarsh, and especially those that quantify extent, specify their terms of reference. •Two definitions of saltmarsh are in use derived from EU Directives.•These two saltmarsh definitions confuse and conflict.•Directive definitions depart from literature definitions.•Halophytes are essential in accurate definition of saltmarsh.