Habitat Action Plan

Coastal saltmarshes in the UK (also known as 'merse' in Scotland) comprise the upper, vegetated portions of intertidal mudflats, lying approximately between mean high water neap tides and mean high water spring tides. For the purposes of this action plan, however, the lower limit of saltmarsh is defined as the lower limit of pioneer saltmarsh vegetation (but excluding seagrass Zostera beds) and the upper limit as one metre above the level of highest astronomical tides to take in transitional zones.

Saltmarshes are usually restricted to comparatively sheltered locations in five main physiographic situations: in estuaries, in saline lagoons, behind barrier islands, at the heads of sea lochs, and on beach plains. The development of saltmarsh vegetation is dependent on the presence of intertidal mudflats.

Saltmarsh vegetation consists of a limited number of halophytic (salt tolerant) species adapted to regular immersion by the tides. A natural saltmarsh system shows a clear zonation according to the frequency of inundation. At the lowest level the pioneer glassworts Salicornia spp can withstand immersion by as many as 600 tides per year, while transitional species of the upper marsh can only withstand occasional inundation.

The communities of stabilised saltmarsh can be divided into species-poor low-mid marsh, and the more diverse communities of the mid-upper marsh. On traditionally grazed sites, saltmarsh vegetation is shorter and dominated by grasses. At the upper tidal limits, true saltmarsh communities are replaced by driftline, swamp or transitional communities which can only withstand occasional inundation. Saltmarsh communities are additionally affected by differences in climate, the particle size of the sediment and, within estuaries, by decreasing salinity in the upper reaches. Saltmarshes on fine sediments, which are predominant on the east coasts of Britain, tend to differ in species and community composition from those on the more sandy sediments typical of the west. The northern limits of some saltmarsh species also influence plant community variation between the north and south of Britain.

Saltmarshes are an important resource for wading birds and wildfowl. They act as high tide refuges for birds feeding on adjacent mudflats, as breeding sites for waders, gulls and terns and as a source of food for passerine birds particularly in autumn and winter. In winter, grazed saltmarshes are used as feeding grounds by large flocks of wild ducks and geese. Areas with high structural and plant diversity, particularly where freshwater seepages provide a transition from fresh to brackish conditions, are particularly important for invertebrates. Saltmarshes also provide sheltered nursery sites for several species of fish.

Since medieval times, many saltmarshes have been reduced in extent by land claim. This practice continued until very recently; for instance, in the Wash 858 ha of saltmarsh were converted to agricultural use between 1970 and 1980. The land enclosed by sea walls was originally converted to grazing marsh with brackish ditches, but since the 1940s large areas of grazing marsh have been agriculturally improved to grow arable crops. As a consequence, many saltmarshes now adjoin arable land, and the upper and transitional zones of saltmarshes have become comparatively scarce in England. Sites still displaying a full range of zonation are particularly valuable for nature conservation. In Scotland and Wales, transitions (eg to freshwater, grassland and dune communities) are still comparatively common. In Northern Ireland most saltmarsh is composed of mid- and upper saltmarsh vegetation with transitions to freshwater or grassland.

The most recent saltmarsh surveys of the UK estimate the total extent of saltmarsh (including transitional communities) to be approximately 45,500 ha (England 32,500 ha, Scotland 6747 ha, Wales 6089 ha, and Northern Ireland 215 ha).This resource is concentrated in the major estuaries of low-lying land in eastern and north-west England and in Wales, with smaller areas in the estuaries of southern England, the firths of eastern and south-west Scotland and the sea loughs of Northern Ireland; north-west Scotland is characterised by a large number of very small saltmarsh sites at the heads of sea lochs, embayments and beaches. It is estimated that, at the mean high water line, 24% of the English coastline, 11% of the Welsh coastline and 3% of the Scottish coastline consists of saltmarsh vegetation.

The following BAP priority species have significant populations on saltmarsh: the eyebright Euphrasia heslop-harrisonii, the ground beetles Amara strenua and Anisodactylus poeciloides, natterjack toad Bufo calamita, the narrow-mouth whorl snaill Vertigo angustior, and endemic sea-lavenders Limonium spp.

Land claim

Large scale saltmarsh land claim schemes for agriculture are now rare. Piecemeal smaller scale land claim for industry, port facilities, transport infrastructure and waste disposal is still comparatively common, and marina development on saltmarsh sites occurs occasionally. Such developments usually affect the more botanically diverse upper marsh and landward transition zones.

Erosion and 'coastal squeeze'

Erosion of the seaward edge of saltmarshes occurs widely in the high energy locations of the larger estuaries as a result of coastal processes. There is evidence that this process is exacerbated both by the isostatic tilting of Britain towards the south-east, and by climatic change leading to a relative rise in sea level and to increased storminess. Many saltmarshes are being 'squeezed' between an eroding seaward edge and fixed flood defence walls. The erosional process is exacerbated in some locations by a reduced supply of sediment. 'Coastal squeeze' is most pronounced in south-east England, where, for example, it is estimated that 20% of the saltmarsh resource in Kent and Essex was lost between 1973 and 1988. The best available information suggests that saltmarshes in the UK are being lost to erosion at a rate of 100 ha a year. In more western and northern regions, there is recent evidence of a trend towards net sea level rise which may be causing saltmarsh erosion, although the rates of loss are not known.

Accretion

Accretion and development of saltmarsh is occurring on parts of the British coastline, notably in north-west England where sediments are comparatively coarse and isostatic uplift largely negates sea level rise. However this accretion is not sufficient to offset the national net loss of saltmarsh, and in many cases the newly created habitats differ from those being lost due to the regional differences referred to in 1.1.4.

Sediment dynamics

Local sediment budgets may be affected by coast protection works, or by changes in estuary morphology caused by land claim, dredging of shipping channels and the impacts of flood defence works over the years.

Cord grass

The small cordgrass, Spartina maritima, is the only species of cordgrass native to Great Britain. The smooth cordgrass, S. alterniflora, is a naturalised alien that was introduced to the UK in the 1820s . This introduction led to its subsequent crossing with S. maritima resulting in both a sterile hybrid, Townsend?s cordgrass S. townsendii, and a fertile hybrid, commoncordgrass S. anglica. The latter readily colonises mudflats and has spread around the coast. It has also been extensively planted to aid stabilisation of mudflats and as a prelude to land-claim. Common cordgrass often produces extensive monoculture swards of much less intrinsic value to wildlife, and in many areas is considered to be a threat to bird feeding grounds on mudflats. As a result, attempts have been made to control it at several locations, although in some areas it is undergoing dieback for reasons not fully understood.

Grazing

Grazing has a marked effect on the structure and composition of saltmarsh vegetation by reducing the height of the vegetation and the diversity of plant and invertebrate species. Intensive grazing creates a sward attractive to wintering and passage wildfowl and waders, whilst less intense grazing produces a tussocky structure which favours breeding waders. In recent decades, some grazed saltmarshes have been abandoned, leading to domination of the mid to upper marsh by rank grasses. Intensive grazing is considered to be a problem in some areas.

Other human influences

Saltmarshes are affected by a range of other human influences including waste tipping, pollution, drowning by barrage construction, and military activity. Turf cutting is a traditional activity in some areas. Oil pollution can potentially destroy saltmarsh vegetation and whilst it usually recovers, sediment may be lost during the period of die-back. The effects of recreational pressure are not well understood but may be locally significant. Agricultural improvement (re-seeding and draining) has affected the upper edge and transition zones of some saltmarshes in the past and may still occur on a small scale. Eutrophication due to sewage effluent and agricultural fertiliser run-off has caused local problems of algal growth on saltmarshes.

Approximately 80% of the area of saltmarsh in Great Britain has been notified as SSSI, except in north-west Scotland where only about 50% has been notified. In Northern Ireland, five of the seven estuaries containing saltmarsh have been declared as ASSI.

Atlantic Salt Meadows is listed as habitat type in Annex I of the EC Habitats Directive. Ten areas in Great Britain have been proposed as SACs for their saltmarsh features. In addition, 27 major saltmarsh sites and many smaller ones are included in SPAs under the EC Birds Directive and in Ramsar sites.

Environmental impact assessment is a statutory requirement for certain proposed developments where there is likely to be a significant effect on the environment.

The UK Government has set out its commitment to sustainable management of the coast in a number of publications. These include DETR's (formerly DoE) Policy Guidelines for the Coast and Planning Policy Guidance - Coastal Planning (PPG 20), and SO's Coastal Planning (NPPG 13). A Coastal Planning Technical Advice Note has been produced for Wales. DoE(NI)'s Planning Strategy for Rural Northern Ireland has provisions relating to development, access and conservation of the coast. MAFF and the Welsh Office have also produced a Strategy for Flood and Coastal Defence in England and Wales and DETR has produced Coastal Zone Management - Towards Best Practice.

DETR's Coastal Forum was set up in 1994; similar fora have recently been initiated in Scotland and Wales, and one is expected shortly in Northern Ireland. Some country nature conservation agencies have their own coastal initiatives (Estuaries Initiative in England, and Focus on Firths in Scotland), and Arfordir is a partnership of coastal practitioners in Wales. In England, MAFF's Habitat Scheme includes a saltmarsh re-creation option for agricultural land behind sea walls (60 ha under agreement in 1997). Countryside Stewardship in England also offers a saltmarsh management option (3977 ha under agreement in 1997 mainly in relation to grazing). In Wales, 291 ha had been entered into CCW's pilot agri-environmental scheme, Tir Cymen, by 1997. The new Welsh whole farm agri-environment scheme, which will include opportunities for the management and restoration of saltmarsh habitats, was launched in 1999. Grazing of traditionally grazed saltmarshes is encouraged on a number of NNRs, SSSIs and ASSIs; prominent examples are the Ribble and the Wash in England, the Solway in Scotland and the Dyfi in Wales. Reintroduction of appropriate levels of grazing where it was carried out in the past and where there are benefits for nature conservation has been undertaken at a number of sites such as the Wash, the Solway Firth and Orfordness in Suffolk. The Merse Management Scheme developed by SNH aims to encourage traditional grazing practices on the Scottish Solway. This scheme, together with other incentives in Scotland, brings 1783 ha of saltmarsh into positive management.

Recent work led by the EA has promoted the role that saltmarshes have in reducing the wave energy reaching the sea wall. Flood defence costs can therefore be reduced in the long term by setting back lines of defence and by allowing saltmarsh development seaward of the defences . MAFF and NE have cooperated on a 21 ha experimental managed realignment and saltmarsh creation scheme at Tollesbury in Essex where the sea wall was breached in 1995 and saltmarsh plants are colonising successfully. Other saltmarsh creation schemes have been undertaken at locations in England, Scotland and Wales. Experimental works have been carried out to protect saltmarsh shorelines from erosion, including brushwood 'polders', offshore barriers and beach recharge.

The National Rivers Authority (now the Environment Agency) published A Guide to the understanding and Management of Saltmarshes in 1995. In the same year, English Nature published Managed retreat - a practical guide. A summary of the initial results from the Tollesbury experiment was produced in 1997.

The Joint Nutrient Study (JoNuS) sponsored by DETR and MAFF, has highlighted the importance of intertidal areas in controlling eutrophication in estuaries.

The successful implementation of the habitat action plans will have resource implications for both the private and public sectors. The data in the table overleaf provide an estimate of the current expenditure on the habitat, primarily through agri-environment schemes and grant schemes, and the likely additional resource costs to the public and private sectors. These additional resource costs are based on the annual average over 5 and 10 years. The total expenditure for these periods of time is also given. Three-quarters of the additional resources are likely to fall to the public sector.

Adam, P. 1990. Saltmarsh Ecology. Cambridge University Press Cambridge.

Allen, J.R.L. & Pye, K. 1992. Saltmarshes: Morphodynamics, conservation and engineering. Cambridge University Press, Cambridge.

Burd, F. 1989. The saltmarsh survey of Great Britain. An inventory of British saltmarshes. Research and Survey in Nature Conservation No. 17, Nature Conservancy Council, Peterborough.

Burd, F. 1992. Erosion and vegetation change on the saltmarshes of Essex and North Kent between 1973 and 1988. Research and Survey in Nature Conservation No.42, Nature Conservancy Council, Peterborough.

Burd, F. 1995. Managed retreat: A practical guide. English Nature, Peterborough.

Davidson, N.C., D. A. Laffoley, D., Doody, J.P., Way, L.S., Gordon, J., Key, R., Drake, C.M., Pienkowski, M.W., Mitchell, R. & Duff, K.L. 1991. Nature conservation and estuaries in Great Britain. Nature Conservancy Council, Peterborough.

Department of the Environment. 1992. Planning Policy Guidance for the coast (PPG 20). HMSO, London.

Department of the Environment. 1995. Policy guidelines for the coast. HMSO, London.

Department of the Environment. 1996. Coastal zone management-towards best practice. HMSO, London.

Lee, E.M. 1998. The implication of future shoreline management on protected habitats in England and Wales. R&D Technical Report W150, Environment Agency, Bristol.

Environment Agency.1995. A guide to the understanding and management of saltmarshes. R & D note 324, Environment Agency, Bristol.

Gray, A.J., & Benham, P.E.M. 1990. Spartina anglica - a research review. Institute of Terrestrial Ecology.

Gray, A.J., Marshall, D., & Raybould, A.F. 1991. A century of evolution in Spartina anglica. Advances in Ecological Research, 21 , 1-62.

Institute of Terrestrial Ecology. 1998. Managed realignment at Tollesbury and Saltram. Report to MAFF, project CSA 2313.

Joint Nature Conservation Committee. 1997. Coasts and seas of the United Kingdom. Coastal Directories series, Joint Nature Conservation committee, Peterborough.

Ministry of Agriculture, Fisheries and Food. 1993. A strategy for flood and coastal defence in England and Wales. MAFF PB 1471.

Ministry of Agriculture, Fisheries and Food. 1993. Coastal defence and the environment: A guide to good practice. MAFF PB 1191.

Ministry of Agriculture, Fisheries and Food. 1995. Shoreline Management Plans: A guide for coastal defence authorities. MAFF PB 2197.

Pye, K. & French, P.W. 1992. Targets for coastal habitat creation. Unpublished report to English Nature, Peterborough (F72-04-22/ES22).

Stewart, A., Pearman, D.A. & Preston, C.D. 1994. Scarce plants in Britain. Joint Nature Conservation Committee, Peterborough.

Duncan Huggett, Environment Agency Tel:

The following LBAPs are working on Coastal saltmarsh:

Originally published in: UK Biodiversity Group Tranche 2 Action Plans - Volume V: Maritime species and habitats (October 1999, Tranche 2, Vol V, p129)