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| Sefton Coast Partnership | Shoreline Management | Nature and Wildlife | Coastal Heritage | Visiting the Coast | Students and Teachers | Coastlines | |
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Summer 1996Saltmarsh PlantsArticle by Peter Gateley, a local botanistConsidering the harshness of the environment it seems amazing how many plants are adapted to life in a salt marsh. As a career move things don't look very promising for a flowering plant in this situation, having to stand for a lifetime in soft shifting mud on an open shoreline or estuary exposed to all sea breezes and then being regularly covered in silt-laden salt water, salt usually meaning death to most of our plants! Yet National Vegetation Classification defines forty-nine plant communities and sub-communities found in salt marshes around the British Coast, each characterised by a different species of group species. Because of where they live salt marsh plants have adapted in a number of ways. Generally they have a hard shiny or soft waxy coating to retain moisture within the plant and to exclude salt, many of them have fleshy succulent leaves or stems for storing freshwater. Other features include stomata which close when the plant is under water and buoyant, salt-resistant, seeds which float with the tides. Two examples of common salt marsh pioneers, found locally, illustrate varying strategies adopted by plants for surviving and succeeding in this environment. Firstly there are the annual glassworts, for examples Long-stalked Glassworts Salicornia dolichostachya, which grow in bare mud and establish very rapidly each year from water-dispersed seed. These plants appear to be composed of fleshy green beads, with thick waxy skins, threaded onto thin stringy stems. These succulent morsels were once commonly collected and eaten as “samphire”. Also in the bare outer zones of “frontline” salt marsh Common Cord-grass Spartina anglica grows. This is a taller slender plant with hard and shiny stems, it is perennial with a tufted habit and forms clumps, then patches and then complete swards, sometimes many hundreds of square metres in extent. It too establishes from seed, but also from broken-off rhizome fragments washed onto the mud, which readily root and grow into new plants. Once plants are established the begin to have a similar effect to that of the dune grasses, Sand Couch and Marram, but rather than trapping sand sediment blown in by the westerly winds they begin to grab much smaller silt and mud particles carried by tides and currents. Sedimentation in Spartina stands can be 5cm to 10cm vertically every year and the spread of muddy salt marsh, south from the Ribble Estuary towards Southport Pier, can largely be attributed to the considerable pioneering and silt-trapping qualities of this single species. Once sediments begin to accumulate more species are able to colonise and spread, eventually a whole salt marsh system develops, ranging from the true pioneers on the seaward edge to dense swards inland. Between mean low water and mean high watermarks, the salt marsh is regularly inundated by salt or brackish water twice a day. Above the mean high water mark is a zone reached only by the high spring tides; still regularly flooded but less frequently so allowing extra, less adapted, species to survive. Above the normal tides an even wider range of plants can grow, able to tolerate the infrequent flooding of the storm flood tides perhaps once or twice a year. These denser inland salt marsh swards merge into dry land or freshwater plant communities. Within an established salt marsh the various plant communities correspond with the differing zones of conditions they need to tolerate. Further complexity is added by the pattern of drainage from the higher inland marsh, where sedimentation has been occurring for longest, down to the sea. This drainage results in networks of muddy creeks, often edged with strips of low grey bushes of Sea Purslane Atriplex portulacoides, a perennial shrubby species which typifies creed edges and which can be useful in identifying these features when walking out in the salt marshes. Many salt marsh species have a wide range of tolerance, some can be found as pioneers out in the open mud and in closed mixed communities throughout later successional stages. Example of such plants found in Sefton's salt marshes, in the Ribble and Alt estuaries, are Spear-leaved Orache, Atriplex prostrata, Common salt marsh-grass, Puccinellia maritima , Sea Plantain, Plantago maritime, and the glassworts, Salicornia species. Small clumps of Puccinellia can often be seen amongst the sparse Spartina and Salicornia on the outer edges of the salt marshes, but also as dense green swards further inland. Buoyant seeds of many annual species, are carried over the entire area of the salt marsh in flood tides and can grow in any suitable gap in the vegetation. Other species regularly encountered in our local salt marshes include:- Sea Arrow-grass, Triglochin maritime, Frosted Orache, Atriplex laciniata, Grass-leaved Orache, Atriplex littoralis, Sea Aster, Aster tripolium, Annual Sea-blite, Suaeda maritime, Sea Milkwort, Glaux maritime, Saltmarsh Rush, Juncus gerardii, Sea Club-rush, Bolboschoenus maritimus, Common Scurvygrass, Cochlearia officinalis, and Red Fescue Festuca rubra. As can be seen from this list, plants from a wide range of unrelated families have made similar adaptations to grow in this fascinating habitat. Many of them can be easily seen in the small accessible salt marsh patches at Hightown. If the much larger Ribble salt marsh is to be explored then great attention needs to be paid to tide times and heights and great care taken in the network of muddy creeks; never explore by yourself, unless you are very experienced. It is worth finding some friends and getting all the correct information, including the weather forecast and setting off into the salt marshes to look for these amazing plants. Take care not to disturb any nesting birds. And, most importantly, tell someone where you are going. Remember also that the Ribble marshes form part of a National Nature Reserve: for permits for group visits or information contact the Site Manager.
Old Hallow
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