Habitat & Species

• Habitats
  • Chalk rivers
  • Calcareous grassland
  • Coastal mudflats
  • Coastal and floodplain grazing marsh
  • Coastal saline lagoons
  • Coastal Saltmarsh
  • Coastal sand dunes
  • Coastal vegetative shingle
  • Eutrophic lakes
  • Fens
  • Lowland acid grassland
  • Lowland heathland
  • Lowland meadow
  • Maritime cliffs and slopes
  • Mesotrophic lakes
  • Native broadleaf woodland
  • Offshore sands and gravel
  • Seagrass beds
  • Arable Field Margins
• Species
• Habitat Targets
• Species Targets

Coastal mudflats

What are they?

Mudflats are sedimentary, intertidal habitats created by deposition in low energy coastal environments, particularly estuaries and other sheltered areas. Their sediment consists mostly of silts and clays with a high organic content. Towards the mouths of estuaries where salinity and wave energy are higher, the proportion of sand increases.

They are intimately linked by physical processes too, and may be dependent on other coastal habitats such as soft cliffs and saltmarshes. Mudflats commonly appear in the natural sequence of habitats between sub-tidal channels and vegetated saltmarshes. In large estuaries they may be several kilometres wide and commonly form the largest part of the intertidal area of estuaries. However, in many places they have been much reduced by land claim.

Like other intertidal areas, mudflats dissipate wave energy, thus reducing the risk of eroding saltmarshes, damaging coastal defences and flooding low-lying land. The mud surface also plays an important role in nutrient chemistry. In polluted areas, organic sediments sequester contaminants and may contain high concentrations of heavy metals.

Highly productive areas, mudflats - together with other intertidal habitats - support large numbers of predatory birds and fish. They provide feeding and resting areas for internationally important populations of migrant and wintering waterfowl, and are also important nursery areas for flatfish. They are widespread in the UK with significant examples in the Wash, the Solway Firth, Mersey Estuary, Bridgwater Bay and Strangford Lough.

Mudflats are characterised by high biological productivity and abundance of organisms, but low diversity with few rare species.

The JNCC Marine Nature Conservation Review (MNCR) biotope codes for mudflats are:

• Sandy mud shores (LMU.SMu)
• Soft mud shores (LMU.Mu)
• Muddy sand shores (LMS.MS).

In areas of lowered salinity, the macro-invertebrate fauna is predominantly of the Petersen Macoma community, characteristic species being: common cockle Cerastoderma edule, sand-hopper Corophium volutator, laver spire shell Hydrobia ulvae, ragworm Hediste diversicolor and, when salinity is low, large numbers of oligochaete annelids (principally Tubificoidesspp).

With a slight increase in the proportion of sand, the polychaetes catworm Nephtys hombergiand lugworm Arenicola marinaoccur. In slightly coarser areas, seagrass (Zosteraspp) beds may develop. Where stones and shells provide an initial attachment for byssus threads, beds of the common mussel Mytilus edulisoccur and accrete material through faecal deposition. Occasional stones or shells may also provide suitable attachment for stands of fucoid macroalgae such as Fucus vesiculosus or F. spiralis.

The surface of the sediment is often apparently devoid of vegetation, although mats of benthic microalgae (diatoms and euglenoids) are common. These produce mucilage (mucopolysaccharides) that binds the sediment. Under nutrient-rich conditions, there may be mats of the macroalgae Enteromorphaspp or Ulvaspp.

Please see the UK BAP website or the UK BAP habitat definition for more information.

The situation in the South East

The following data is for mud and sand flats. 

 The total UK esturine resource has been estimated as c588,000 ha, of which 55% is intertidal area, mostly mud and sandflats, with a lesser amount of saltmarsh. Intertidal flats cover about 270,000 ha. The UK has approximately 15% of the North West European estuarine habitat.

 Rate of Change

Please follow this link for the 2008 report on the extend and condition of intertidal habitats

Current Threats

The following are the main threats to coastal mudflats in the region:

• Sea level rises. It has been estimated that sea level rise will result in a loss of 8,000 to 10,000 ha of intertidal flats in England between 1993 and 2013. Much of this loss is expected in Southern and South East England. The rise results from sinking of the land following the end of the last Ice Age, plus the effects of global warming. Low water moves landward, but sea defences prevent a compensating landward migration of high water mark, with the result that intertidal flats are squeezed out.
• Land claim. Land claim for urban and transport infrastructure and for industry, has removed about 25% of Great Britain’s estuarine intertidal flats and up to 80% in some estuaries. Loss of mudflats reduces estuary productivity and may influence other estuary habitats such as saltmarsh. Although land claim has slowed considerably in recent years, it has not stopped.
• Barrage schemes. Such schemes for water storage, amenity, tidal power and flood defence continue to pose a threat to the integrity and ecological value of mudflats in estuaries and enclosed bays.
• Pollution. Diffuse and point source discharges from agriculture, industry and urban areas, including polluted storm water run-off, can create abiotic areas or produce algal mats which may affect invertebrate communities. They can also remove embedded fauna and destabilising sediments thus making them liable to erode.
• Extraction. Oil and gas extraction and related activities, and dredging for navigation, have an important effect on sediment biota and on sediment supply and transport. Many coastal areas, including estuaries, are now either licensed or available for exploration and development.
• Fishing. Fishing and bait digging can have an adverse impact on community structure and substratum. For example, suction dredging for shellfish or juvenile flatfish bycatch from the shrimp fisheries may have a significant effect on important predator populations.
• Human disturbance. This affects the roosting and feeding areas of bird populations. 
  
• The introduction of new or non-native species. For example, the spread of cord-grass Spartina anglica which has vegetated some upper-shore mudflat areas with important ecological consequences in some areas.
• Erosion and sedimentation. Within estuaries, mudflats deposited in the past may erode due to changed estuarine dynamics and re-mobilised sediment may be redeposited elsewhere in the same littoral sediment cell. Higher sea level and increased storm frequency, resulting from climate change, may further affect the sedimentation patterns of mudflats and estuaries.

 Vision for coastal mudflats

The South East Biodiversity Forum’s vision for this habitat is that there should be:

• No further loss of existing habitat
• Good management, including visitor management, on all extant sites
• No damage to site integrity from activities arising outside the sites, eg. inadequately managed public access
• Re-creation of sand dunes on appropriate sites to restore some past losses, including the linking up of fragmented sites • Greater public appreciation of sand dunes and their specialist wildlife, including greater awareness of the impacts of human pressures, such as dog-walking, mountain-biking, dumping of waste
• Creation of alternative green space around important sand dunes under pressure for increasing new housing