Saltmarsh

Spectacular coastal wetlands that channel the tides and pulse with life.

What is a saltmarsh?

Saltmarshes are dynamic coastal wetlands that host a huge variety of wildlife, from familiar faces like redshank, shelduck and skylarks to uniquely adapted plants and invertebrates such as marsh samphire or the sea aster mining bee.

Survival on these ever-changing landscapes means braving the threats of sudden salt water torrents, thick layers of sediment being deposited every year and the pull of the tides themselves.

But, as their salty mud never freezes, and hardy plants flower from February to September, they also represent uniquely reliable foraging grounds even in the dead of winter.

How do saltmarshes store carbon?

Saltmarshes are also planet-protecting powerhouses, with restored saltmarshes known to capture carbon as much as 40 times faster than forests.

Many saltmarsh plants grow rapidly in the spring and summer, drawing CO2 out of the atmosphere as they photosynthesise, only to be buried by layers of sediment carried by the autumn’s high tides.

Locking these plants underground prevents them from releasing greenhouse gases as they decompose and gives the next generation room to grow.

What lives on a saltmarsh?

Saltmarshes are weapons of mass creation that burst with life all year round. Every niche is filled and many of the creatures that call saltmarshes home are found nowhere else on earth, making them incredible biodiversity-boosting habitats.

Around 40 species of plants occur on saltmarshes in Britain. These hardy plants are uniquely adapted to the harsh, saline conditions, enabling them to colonise vast areas that would otherwise be barren mud.

Saltmarshes are teeming with invertebrate life, including worms, snails and beetles. Of the 290 species of terrestrial invertebrates known to live on saltmarshes in the UK, a whopping 148 rely on our intertidal habitats for survival. These include the saltmarsh shortspur beetle, Narrow-mouthed whorl snail and sea aster mining bee. This unique bee times its late emergence precisely with the blooming of the sea aster, a saltmarsh plant,demonstrating the intricate relationships in the ecosystem.

Which birds can be found on saltmarshes?

Saltmarshes are important for both resident and migratory birds, including redshank, skylark, curlew, egrets, dunlin and spoonbills. So far, WWT Steart Marshes has recorded 80 wetland bird species using their reserve in Somerset.

Some use the high grasses as cover in which to raise their young, others use the mudflats as sources of fish, molluscs and insects. The curlew, with its distinctively long, curved bill, uses masses of mini sensors to detect prey hidden in the mud.

Do mammals, fish or amphibians live on saltmarshes?

The intricate networks of creeks and pools in saltmarshes provide essential habitats for various fish species. These areas act as nurseries and refuges for the critically endangered European eel and other species like herring, thin-lipped grey mullet, flounder, sand smelt and three-spined stickleback.

The upper reaches of saltmarshes support a variety of mammals, including shrews, mice and water voles who feed on the abundant invertebrates. Otters have also been spotted in some restored saltmarsh areas, like WWT Steart Marshes.

Despite the saline conditions, some amphibian species have adapted to life in saltmarshes. The natterjack toad, a protected species in the UK, is a prime example. These resilient amphibians have evolved to breed in diluted brackish pools within the saltmarsh.

Saltmarsh and flooding

As well as being vital for biodiversity, supporting everything from critically endangered European eels to stately spoonbills, saltmarshes have tremendous value to coastal communities.

Thanks to their networks of timeworn creeks and thick, springy grasses, saltmarshes absorb tidal energy, slowing water down, trapping it in pools and reducing the wear and tear on manmade flood defences that sit behind them during storms.

Where do you find saltmarshes?

Saltmarshes can be natural or created by experts where conditions are suitable. They form in sheltered places along the coast, particularly in estuaries like the Thames, The Wash, Solway Firth and Severn Estuary.

They’re created when mud and silt are deposited along a sheltered part of the coastline. Small plants known as ‘pioneer’ species take root, followed by larger plants and organisms. These in turn trap more sediment and as the saltmarsh builds up, more plants become established in the wetland.

Because each plant has its own level of tolerance to water and tidal flooding, a saltmarsh naturally supports a variety of plants.

They’re found in most parts of the world where there’s low-lying land and a temperate climate. In the tropics and sub tropics they’re replaced by mangroves.

How are saltmarshes created?

As well as natural, ancient saltmarshes, it is possible to create saltmarshes through a process known as managed realignment. This involves deliberately breaching sea defences that protect low-lying land at risk of flooding to let the sea in, and building stronger defences further inland.

In this way the cost of maintaining old flood defences is effectively removed, stronger new defences protecting homes and businesses are given a buffer of protective saltmarsh and seeds carried by the tides will colonise the newly intertidal land in the course of just a few years.

What threats do saltmarshes face?

Since 1860 more than 85% of England’s saltmarshes have been lost, either to rising sea levels or changes in land use. As far back as the Romans, human desire for more and more farmland has seen saltmarshes being drained and ‘reclaimed’ from our seas and estuaries. More recently we’ve drained them to expand our cities and build new airports.

Saltmarshes and the wildlife that live in them are also threatened by climate change. Globally, rising sea levels and increasingly frequent and damaging storms are putting them under pressure.

Without human intervention saltmarshes would gradually creep inland as sea levels rise, slowly raising the land up with layers of sediment and providing a natural sea defence. However, in places where we have constructed sea walls close to the water this natural process stops, with saltmarsh plants inundated more freuquently and eventually dying off entirely.

Restoring saltmarshes

Despite the threats saltmarshes face, there is good news. Unlike rainforests, which can take centuries to recover, saltmarshes can reform and start providing valuable habitats within just a matter of years.

WWT Steart Marshes is a brilliant example of this. It is one of the largest wetland creation projects in the UK, restored by WWT and the Environment agency as part of an ambitious project to harness the power of saltmarshes.

The site boasts an incredible record when it comes to species diversity. In just ten years over 500 species of flora and fauna have been recorded on site.

These include 375 plants species, 80 different species of bird, at least 11 different species of fish and 26 different mammals including otters, voles and more bats than before the site was turned into a saltmarsh.

As well as its amazing biodiversity it is also a deeply valued community asset, providing a place for people to connect with nature, for farmers to produce the finest saltmarsh lamb and beef and capturing huge quantities of carbon in its first decade.