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Saltmarsh

What is saltmarsh? 

Salt marshes are a habitat that are home to a rich variety of plants and animals. Salt marshes are coastal wetlands that are periodically flooded and drained by the tides from the sea. They are populated by plants and animals uniquely adapted to living there. 

Saltmarsh is found on the upper part of the mudflats, an area that the sea reaches only when the tide is high. It is covered in plants that can cope with salt and with being regularly underwater. Salt marsh can look quite plain and non-descript but if investigated more closely, it is not so much what you see on the surface (although plants like Samphire/Glasswort and sea purslane are fascinating in how they have adapted to the harsh environment) but what lies beneath in the mud, and what an incredible food source for birds all the invertebrates are. In fact, saltmarshes are incredibly intricate, dynamic habitats where land meets the sea. They are highly productive ecosystems, rich in birds, plants and insects. Their ecological value for the ecosystem is mainly in nutrient regeneration, primary production (production of chemical energy in organic compounds by living organisms), habitat for wildlife species, shoreline stabilizers and they also act as carbon sinks.  So as the saying goes "don't judge a book by its cover". 

Good examples of salt marsh can be seen along the Solent, examples being Chichester harbour, Bunny Meadows near Warsash, Lymington and Keyhaven Nature Reserve and Newtown on the Isle of Wight. 

 

How is saltmarsh formed? 

Salt marshes start life as mudflats. In areas of sheltered water, like a harbour, the sediment held in the water settles out and builds up. The structure of saltmarsh is created by the way that water moves, as waves dissipate their energy and deposit silt during higher spring and storm tides and the water then runs back off the marsh. The latter process creates branching creeks that drain the marsh, from small meandering ditches, to waist-deep, fast-flowing channels with slippery, muddy sides. When the accumulating mud rises above the water surface on average tides (halfway between spring and neap tides), saltmarsh plants can colonise. These capture more sediment and allow the marsh to keep building for as long as it is still low enough to be flooded by the higher tides. As the mudflats build up, different types of plants can grow and live there creating a salt marsh habitat made up of blocks of flat low growing vegetation with narrow channels between. The development of mudflats and saltmarsh over time is known as succession. 

 

Birds of the saltmarsh 

Golden Plover in Saltmarsh Large marshes have an abundance of salt tolerant plants that attract insects, so are full of food for birds. Saltmarshes are important areas for small creatures such as worms, shrimps and shellfish, fish, wading birds and wildfowl. They provide nursery areas for fish, food for waders and wildfowl and nesting sites for waders and seabirds. Redshanks, Black-headed Gulls, Mediterranean Gulls and Mallards nest in these places in the summer. About 25,000 pairs of redshanks are thought to breed in the United Kingdom with about half of these nesting in coastal saltmarshes. 

When the high tide covers the mud flats, birds such as curlew, godwits, redshank, and dunlin, which feed on creatures in the mud, need somewhereCurlew in saltmarsh like the saltmarsh to roost, rest, and preen. When the tide is very high even the saltmarshes are covered by water and the birds need to find other places to rest.  

Saltmarsh can attract rare species, such as spoonbill, glossy ibis and black-winged stilt and migrant visitors, including Brent geese. With so much wildfowl around, often birds of prey patrol, including peregrine, merlin and hen harrier! 

 

Plants of the saltmarsh 

The flora of a salt marsh is differentiated into levels according to the plants' individual tolerance of salinity and water table levels. Vegetation found at the water must be able to survive high salt concentrations, periodical submersion, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower marsh zones are determined through the ability of plants to tolerate physiological stresses such as salinity, water submergence and low oxygen levels. 

Saltmarsh vegetation shows a clear zonation according to how often it gets covered in seawater. Plant species diversity is relatively low, since the flora must be tolerant of salt, complete or partial submersion, and anoxic (lack of oxygen) mud substrate. The saltmarshes are first vegetated with samphire and then with cord-grasses, sea purslane, sea aster and sea lavender as the mud becomes drier.   

The most common salt marsh plants are glassworts (Salicornia spp.) and the cordgrass (Spartina spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat and begin its ecological succession into a salt marsh. The glassworts can withstand immersion by as many as 600 tides per year, whereas species of the upper marsh can only withstand occasional inundation. The lower marsh has the fewest species, the upper marsh a much more diverse community. Where the saltmarsh is grazed the vegetation is shorter and there are more grasses. Spartina anglica is an invasive hybrid cordgrass. This hybrid has been extensively planted to stabilise mudflats as a prelude to land reclamation and is spreading along the coast, often producing extensive monoculture swards of reduced wildlife value. Thick swards of Spartina prevent the usual communities of annual glassworts Salicornia spp from maintaining themselves on the seaward edge of the marsh. This has detrimental effects on invertebrate communities and can reduce use by shorebirds and wildfowl by reducing the food supply and increasing the vegetation height.