The Salt Marsh System

Salt marsh vegetation is found on most muddy coasts in the temperate areas of the world. It is easily recognized as it exhibits a very definite community structure. It is made up of distinct zones of vegetation parallel with the shore line each with different plants from its neighboring zone, although some overlap is inevitable.

The best time to observe the salt marsh community is at low tide when all of the zones are visible. On the mud flats nearest the sea will be green filamentous algae, very fine seaweeds, which catch on to rocks and lumps of mud. Slightly higher up the marsh the same algae will be found draped around the plants along the shore, as they are carried up the beach at high tide.

The first plant to root in the mud is usually the glass-wort (Salicornia), a small succulent plant highly adapted to its environment; it is tolerant of very high salinity, a constantly waterlogged soil and being covered by the sea at every high tide. The roots of Salicornia begin the stabilization of the mud and allow other plants to become established.

The first of these is probably the plant most commonly associated with salt marsh, the reed, Spartina. This plant is so successful in its habitat that despite the fact that it has only recently been introduced into Britain it is already found in most areas. It is very fast growing and its creeping growth habit means that it binds the shifting mud, very effectively stabilizing it to allow colonization by less highly adapted plants.

As soil build-up occurs in the upper regions of the marsh, there is a marked increase in the vegetation found and also in the number of halophytic (salt-tolerant) species. The reclaimed land is known as the emergent marsh, and is often marked by a small ‘cliff in the mud. The stable soil quickly establishes a mixed marsh community, namely salt marsh turf. The species present include sea plantain (Plantago), sea lavender (Limonium), thrift (Armeria), rushes (Juncus) and many others.

These plants are noticeably smaller and more compact inform than those of the lower marsh. They also usually have a smaller woody rhizome compared with the much longer creeping stolon of the Spartina.

The development of the marsh is marked by these zones. A young colony has no emergent marsh but nearly all the mud-fiat plants. As the soil builds up at the top of the marsh, eventually non-halophytes will be able to colonize and the land will have been reclaimed.