Mudflats are composed of deposits of sand, silt & mud in sheltered, intertidal areas. They are usually uncovered at low tide but are submerged at high tide & range from soft mud to firm sands.

Key Characteristics

  • Site: Low-energy coastal environment
  • Main Species: Benthic microalgae, Enteromorpha, Ulva, Zostera
  • UK: 270,000 ha

Habitat Description

  • Mudflats are formed when sediment encounters a low-energy coastal environment, such as estuaries & sea loughs, where it deposits. Over time the sediment accumulates, making the area flatter & wider, which allows further sediment deposition.
  • The substrate is composed of silts & clays and has a high organic content. In higher energy environments, such as the mouths of estuaries, the substrate is composed of a higher proportion of sand.
  • Mudflats appear to have little vegetation, but mats of benthic microalgae are common, which bind the sediment together. Where there is a higher supply of nutrients, mats of Enteromorpha spp. or Ulva spp. may occur, particularly where salinity is reduced (NIEA, 2005).
  • Coarser substrates support seagrasses Zostera spp. & mussel beds in stony areas. These areas provide attachment sites for stands of fucoid macroalgae such as Fucus spiralis & F.vesiculosus.
  • Mudflats have high biological productivity & abundance of organisms, but are low in diversity with few rare species (UK HAP, 1999)

Current Status in UK & Northern Ireland

Intertidal flats cover an estimated 270,000 ha in the UK.

All larger areas of mudflats in Northern Ireland are located within sea loughs & estuaries. Mudflats are recorded at seven places in NI. Mudflats occur in Lough Foyle, primarily in the lower littoral zone & are covered at half tide, the mouth of the Bann Estuary, the southern end of Larne Lough, Belfast Lough, Strangford Lough, Carlingford Lough & Inner Dundrum Bay.

Mudflats are under threat from direct physical disturbances (e.g. capital or maintenance dredging for navigation), land claim, as they are usually found in sheltered regions near existing developments, making them economically attractive, construction of coastal defences, bait digging, mechanical cockle harvesting, introduced species (e.g. cord-grass Sparina anglica), sea level changes & climate change (higher summer temperatures may lead to increased level of desiccation in the intertidal area & increased storm frequency could increase the level of wave energy in the water column, preventing settlement of fine organic & inorganic materials). Pollution can be particularly damaging, as where there is nutrient enrichment, the green ephemeral seaweed Enteromorpha spp. can form macroalgal blooms which prevents light penetration to the mud surface below.

Designated Sites

  • Bann Estuary
  • Larne Lough
  • Lough Foyle
  • Roe Estuary

Further Information