Just days after the Environment Secretary launched the construction of Europe’s largest human-made coastal nature reserve in Essex, a study from the University of East Anglia has raised serious questions over how effective current efforts to provide habitat for threatened species have been.  

According to researchers at the University of East Anglia, new salt marshes being created as part of managed coastal realignment are failing to meet European conservation regulations. The results of a study published on Thursday (20th September) in the Journal of Applied Ecology, show that current efforts to support some key marshland species are flawed.

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Under the EU Habitats Directive, new salt marsh must be created each time natural salt marsh is lost to coastal development or coastal erosion caused by rises in sea-levels. These new marshes must display “equivalent biological characteristics” to their natural counterparts under EU law – but research has shown the artificially created marshes suffer from reduced biodiversity. 

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“Salt marshes such as those in North Norfolk, Essex and around much of the coast of England are loved by naturalists and tourists alike for their natural beauty and rare/rich ecology,” said lead author Dr Hannah Mossman of UEA’s School of Environmental Sciences, “These unique tidal areas also provide vital habitat for invertebrates, a staging post for migrant birds, and the only environment in which a number of salt-tolerant plants can survive.”

Study investigates marshland biodiversity

Over the course of a five year study, the UEA researchers analysed the vegetation of 18 marshes created through deliberate coastal realignment since 1991 and 17 marshes created accidentally by storm surges since 1881. They compared the salt-tolerant plants at these sites with those at 34 natural salt marshes and found that some key species were very poorly represented. These included sea lavender, thrift, sea arrowgrass and sea plantain.

Rising sea levels caused by global warming are posing a growing threat to the country’s coastal salt marshes and increasing the cost of maintaining sea defences. The UK response to this challenge has so far been to relocate sea walls further inland, allowing new salt marsh to develop.

Although it had been assumed that the process caused no loss of species richness, and that purpose-built marshes compensated well for the loss of natural ones, the researchers discovered plant life on artificially created salt marshes tended to be dominated by early-colonizing plants such as marsh samphire because of a lack of oxygen in the sediment. This led to early establishment of a small number of species, which grew to dominate the areas, excluding others.

The researchers said that “Even the older, accidentally-created marshes were deficient in the characteristic salt marsh perennials such as sea lavender, thrift, sea arrowgrass and sea plantain.” They warned that their findings “demonstrate very clearly that marshes created by managed realignment are not biologically equivalent to natural ones” and said that current methods of ‘biodiversity offsetting’ employed in the UK and throughout Europe are therefore “failing to satisfy the biodiversity requirements of the EU Habitats Directive.” This will come as a blow to Defra, which has put a lot of stock into the concept since April this year. 

UEA professor calls for biodiversity measures to be put into action

Professor Anthony Davy, another EUA biological sciences researcher, clarified that, although his department’s study had identified shortcomings in the current approach to tackling the erosion of coastal habitats, there is still hope to improve practices. He said, “These created marshes are certainly better than losing our precious natural salt marsh altogether, but they are not a good enough replacement. We are currently developing ways of enhancing their biodiversity, such as improving local drainage conditions and planting the deficient species.”

Professor Davy elaborated that, as different plant communities thrive depending on different conditions, a number of measures would have to be taken to benefit different species. He said plants’ successes in these areas are largely dependent on their tolerance of particular conditions such as rocky ground created by ‘consolidated sediments’ or waterlogging. The fact that, at present, many purpose-built marshes are on flat land, without a creek system for drainage, means “flooding-tolerant pioneer species” are favoured,  according to professor Davy.

Recommended measures to support better biodiversity include designing creek systems for purpose-built marshes and introducing more variation in the land, with higher areas and lower pans, both of which will improve drainage in certain areas, enabling the better establishment of underrepresented species. He said that, as an extreme measure, planting ‘plugs’ of nursery-grown threatened species would also help bolster these plants.

Professor Davy said a wide range of stakeholders will be necessary to successfully improve biodiversity in these coastal regions, “We would aim to interact with land owners or managers, conservation organisations, especially RSPB, and Government bodies with responsibility for coastal defence and conservation.”

Wallasea Island reserve

On Monday (17th September), environment secretary Owen Paterson launched the Wallasea Island coastal nature project, which promises to be Europe’s largest reserve of its kind. The reserve, in the Thames Estuary, will be transformed from levee-protected farmland into 670 hectares of wetland. 4.5 million tonnes of clean earth excavated during the construction of new rail tunnels under London will be transported to the site to create higher and lower ground, as recommended by the UEA researchers, with the aim of restoring the area’s wetland landscape of mudflats, saltmarsh and lagoons last seen 400 years ago.

Professor Davy welcomed the project, which he said would present an opportunity to put recommendations made to support a diverse array of species into practice through raising land levels. However, his tone remained one of cautious optimism; the professor elaborated, “The exciting new developments at Wallasea Island are rather different from ‘Managed Realignment’, because they depend on importing material to raise the levels. This huge project represents a great opportunity for creation of salt marsh, among other habitats. However we believe that many of these issues relating to local topography, drainage and the establishment of appropriate vegetation are likely to pertain there, and thus our work should help in avoiding the problems that we have identified.”

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