Key species • British saltmarsh types • Spartina marsh

Key species & communities

Four main general types of saltmarsh are recognised:

• Pioneer marsh
• Low marsh
• Upper marsh
• Transitional marsh

The main species and vegetation types found in these marshes in England and Wales are briefly described below, beginning with the pioneer marshes and thereafter in the order in which they might be encountered progressing from a mudflat to a seawall. An example of the elevation of different saltmarsh habitats in The Wash, is also provided in the table below.

Click here for further information on key species and communities

Pioneer marsh

The three commonest types of pioneer vegetation are Spartina, annual glasswort (Salicornia) and sea aster (Aster tripolium). Spartina marshes, which are often extensive and frequently comprise dense strands of the grass without any other species, are discussed in more detail in the next section. Annual glasswort (made up of various species of Salicornia and known in some areas as Samphire) and sometimes annual sea-blite (Suaeda maritima) form pioneer communities on open mudflats seaward of perennial vegetation. Theirs is essentially an avoidance strategy, germinating and reproducing between the spring and autumn equinoctial tides. In fact, the autumn tides are major dispersal agents, distributing glasswort and sea-blite seeds throughout the saltmarsh. These plants can, therefore, be found as seedlings at any level of the marsh and can survive to reproduce in depressions or pans in the upper marsh.

Sea aster pioneer zones are mainly confined to south east England and largely form dense, pure stands of the rayless form of aster (lacking the lilac ray florets common in asters on the upper marsh). There is some evidence that the rayless form may have arisen relatively recently and that it is genetically different from the rayed form in several ways (other than lacking rays) which have enabled it to spread in the pioneer and low zones of muddy south east saltmarshes.

Several other species may also act as pioneers. Common saltmarsh grass (Puccinelia maritima) is a frequent pioneer on the grazed, sandy marshes of the north west of England and is also found in many estuaries on the edge of marshes fringing their upstream reaches. In the latter instance the marsh is usually brackish marsh and almost any species from the upper levels of the more seaward marshes may colonise the mud at the estuary / tidal river / creek edge. However, the most common are sea club-rush (Scirpus maritimus), various species of orache (Atriplex species) and, in the more freshwater areas, common reed (Phragmites australis) or creeping bent-grass (where the zonation is often reversed, with more salt-tolerant species growing on the upper marsh).