Saltmarshes and mudflats – a case for creation

Hazlewood Marshes - John Lord

Andrew Excell, South East Suffolk Sites Manager, explains the importance of saltmarsh and mudflat habitats for biodiversity and the environment.

It could be so easy to dismiss saltmarshes and mudflats as uninspiring, almost featureless habitats in the estuarine and coastal landscape.  Nothing could be further from the truth of course, as these vital components of the intertidal zone function so positively for the environment on so many counts.

Saltmarshes have a unique and uncommon flora of extremely tough, salt-tolerant plants, capable of withstanding regular immersion in saline waters. This is a land of sea lavender, purslane, aster, spurrey and samphire, and on the higher transitional zones covered by only the biggest tides, grassland species become comfortably juxtaposed with these saline specialists to produce a more species-rich zone. Saltmarsh is a relatively rare UK Biodiversity Action Plan (BAP) habitat, with Suffolk probably having around 2.5-3% of the overall UK figure for this habitat. Estimates of total area vary, but it is well documented by scientific study that overall figures are declining every few years.

Saltmarsh with sea lavender and sea purslane - Terry Whittaker/2020VISION

Saltmarsh with sea lavender and sea purslane - Terry Whittaker/2020VISION

The stabilising effect of the vegetation mat on saltmarsh muds and gravels also makes this habitat a renowned natural defence against wave erosion and damage. Continuous wave energy can have a hugely significant effect on coastal defences such as estuarine walls, and those wall sections with saltmarsh habitat in front always seem to require less frequent maintenance and repair. Wave energy simply gets absorbed into the saltmarsh structure as the gradual shallowing of the water through the marsh breaks up waves before they impact on the wall behind.

Vegetated saltmarsh, complete with intricate rills and channels can perform a crucial role as a fish nursery, allowing smaller fry to shelter in the twice-daily covered channels in warmer waters away from the stronger currents and wave action of the central river. The temporary underwater forests provide refuges from larger predatory fish as well.

Mullet, flounder, stickleback, goby and bass fry from fish surveys at Hazlewood Marshes

Mullet, flounder, stickleback, goby and bass fry from fish surveys at Hazlewood Marshes

At our Hazlewood Marshes reserve, we have been monitoring intertidal development on site since the unplanned realignment following the storm surge of December 5th, 2013. As well as developing 2.6 hectares vegetated saltmarsh since 2013, it is clear just how important this site is shaping up in an estuarine context for fish, with 9 species being recorded in survey work to date. The fry of many species remain between tides within the reedbed and in permanent pools on site, taking advantage of the calmer conditions, plentiful food supply and habitat niche away from larger predators. We are planning additional surveys within the reserve and in the wider estuary to search for smelt, as it is known to spawn in the estuary nearby and is a key species for conservation effort in the Alde, Ore and Butley estuary complex.

Hazlewood Marshes - John Lord

Hazlewood Marshes - John Lord

Saltmarshes also frequently function as key high tide roosting sites for waterfowl and waders, particularly in winter months where huge flocks of waders many thousands strong can be seen alighting on a seemingly impossible spit out in an estuary. Birds are simply seeking a temporary safe refuge away from disturbance where they can take much needed rest before busily feeding on crustaceans and other invertebrates in the estuarine mudflats as soon as they are exposed on the falling tide. At Hazlewood Marshes, we created 15 islands within the intertidal zone back in 2015 and these have readily developed saltmarsh flora from seeds washing in from the wider estuary. They also support significant waterbird roosts and charismatic large waders such as spoonbills, with 29 of these birds being seen on site one peak count.

Spoonbills and cormorants - Angela Lord

Spoonbills and cormorants - Angela Lord

With mudflats, much lies in appreciation of their simple beauty, especially in the right light where intricate channels can be seen meandering over the surface, and artistic lines of silhouetted wading birds can be seen probing for worms and other invertebrates. This is an extremely productive habitat for creatures living in the mud (the benthic layer), being so rich that it attracts migratory birds from great distances to feed in it.  All our Suffolk estuaries are designated Special Protection Areas (SPAs) for the sheer numbers of overwintering birds they support. As an example, the combined Stour and Orwell estuary SPA frequently hosts over 60,000 waterbirds each winter. 

Benthic invertebrate surveys at Hazlewood Marshes - Andrew Excell

Pushing in a soil coring tube to extract a soil core sample for benthic invertebrate surveys at Hazlewood Marshes - Andrew Excell

The power of nature is again demonstrated with our monitoring discoveries at Hazlewood Marshes. Despite being intertidal for less than three years, a benthic invertebrate survey across the site in 2016 showed a widespread abundance of amphipod shrimps, polychaete worms and bivalve molluscs, with species preferences already recorded where saltmarsh plants were established, or where bare muds were fully exposed. Visual signs support these rich invertebrate findings with over 1500 black-tailed godwits regularly feeding on worms within the reserve muds.

Fish survey work at Hazlewood Marshes - Andrew Excell

Hauling in a seine net catch for a fish survey at Hazlewood Marshes - Andrew Excell

Saltmarsh and mudflats have another vital role in the environment, that being their ability to rapidly sequest, or absorb and store carbon from the atmosphere.  Did you know that a single hectare of mudflat absorbs up to 50 times more carbon than the equivalent area of tropical rainforest, for example? This astonishing fact is pushing such ‘blue carbon’ intertidal habitat creation up the agenda on many a coastal forum as a weapon in the fight against climate change. The relative simplicity and scale of habitat creation, plus the many significant wildlife, world health and economic benefits is surely serious food for thought in our modern, often unbalanced world.