Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA2.33 Marine Atlantic littoral mud with associated communities

Marine Atlantic littoral mud with associated communities

Quick facts

Red List habitat type code NEAA2.33
Threat status
Europe Endangered
EU Endangered
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

Intertidal flats along the open coast and near tidal inlets consist mainly of medium to coarse sand. In sheltered areas and near tidal watersheds the sediment is finer and may entirely consist of fine mud. This habitat type can occur in patches or grade into intertidal flats dominated by other soft sediments. Similarly whilst intertidal mudflats in large bays may be considered fully marine, there can still be a river influence and therefore reduced salinities across some of the habitat depending on location and outflow levels. Mudflats in fully marine waters, periodically falling dry at low tide, subject to great amplitudes of temperature, light and salinity, and may be subject to high eutrophication and input of organic substances from rivers and the open sea. Free of vegetation, of higher plants and of macroalgae but mostly covered by thin layers of diatoms and bluegreen algae. In some situations they may be colonised by seagrass. Sediments consist mainly of fine particles, mostly in the silt and clay fraction (particle size less than 0.063 mm in diameter), though sandy mud may contain up to 80% sand (mostly very fine and fine sand), often with a high organic content. Little oxygen penetrates these cohesive sediments, and an anoxic layer is often present within millimetres of the sediment surface. Intertidal mudflats in fully marine open sea (coast) only develop under macrotidal conditions such as those found in the German Bight and Mont Saint Michel, France. Also they form part of a habitat complex on a landscape scale within bays, barrier systems and estuaries. The intertidal mudflats support communities characterised by polychaetes, bivalves, snails and oligochaetes. The species composition of the macrobenthic communities are likely to show zoning from high to lower intertidal levels. In the Dutch, German and Danish Waddens Sea, for example, the high coastal tidal flats are generally characterised by a low number of species with numerous small individuals that are deposit feeders. Typical examples are Corophium volutator and Hydrobia ulvae. Large-sized species become numerous below mean tide levels and below this the biomass is dominated by the deposit feeding Arenicola marina. At mudflats well below mean low water, large filter-feeding bivalves such as Cerastoderma edule, Mya arenaria, Mytilus edulis and Ensis directus make up a significant proportion of the total biomass.

Indicators of quality:

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include: the presence of characteristic species as well as those which are sensitive to the pressures the habitat may face; water quality parameters; levels of exposure to particular pressure, and more integrated indices
which describe habitat structure and function, such as trophic index, or successional stages of development in habitats that have a natural cycle of change over time.

There are no commonly agreed indicators of quality for this habitat, although particular parameters may have been set in certain situations e.g. protected features within Natura 2000 sites, where reference values have been determined and applied on a location-specific basis.

Characteristic species
For full habitat description, please download the habitat factsheet.

Threat status

Synthesis of Red List assessment

There has been a very significant decrease in the extent of this habitat over the last centuries (possibly as much as 80%). The current situation is more stable although some reduction in extent continues, for example coinciding with coastal works such a harbour construction or channel dredging. Comparative studies have also recorded declines in quality in benthic communities of intertidal mudflats in the Waddensea for example biogenic structures disappeared in the 1930s and mussels and cockles decreased and almost disappeared around 1990. Since then recovery is slowly taking place.
Also relevant is the associated decline in the quality of habitat complexes (bays, barrier systems and estuaries) which include intertidal mudflats, but this is difficult to quantify. Localised reductions in quality are still taking place, for example in industrialised areas where the intertidal mudflat habitat may be degraded due to toxic contamination and elsewhere if run-off from the land leads to eutrophication. Invasive species such as the Pacific Oyster and razor clam have also modified the composition of the associated benthic communities, particularly in parts of the Wadden Sea. De-polderisation or managed retreat schemes (e.g. through the partial or total removal of dykes) have been undertaken on a small scale to try and restore areas of intertidal mudflat habitat. Overall the current situation is probably stable and with scope to improve with appropriate conservation and preservation measures. Nevertheless, because of the significant historical reduction in extent of this habitat it is assessed as being Endangered for both the EU 28 and EU 28+.
EU
Red List Category Red List Criteria
Endangered A3
Europe
Red List Category Red List Criteria
Endangered A3

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Fishing and harvesting aquatic resources
    • Hunting, fishing or collecting activities not referred to above
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Pollution to surface waters by industrial plants
    • Pollution to surface waters by storm overflows
    • Diffuse pollution to surface waters via storm overflows or urban run-off
    • Diffuse pollution to surface waters due to agricultural and forestry activities
    • Input of contaminants (synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, acute events
    • Marine water pollution
    • Oil spills in the sea
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Landfill, land reclamation and drying out, general
    • Polderisation
    • Reclamation of land from sea, estuary or marsh
    • Removal of sediments (mud...)
    • Estuarine and coastal dredging
    • Dykes, embankments, artificial beaches, general
    • Sea defense or coast protection works, tidal barrages
  • Climate change
    • Changes in abiotic conditions
    • Water flow changes (limnic, tidal and oceanic)
    • Wave exposure changes
    • Sea-level changes
    • Changes in biotic conditions
    • Habitat shifting and alteration

Habitat restoration potential

Intertidal habitats pose special problems for restoration because (i) they are topographically and ecologically complex, (ii) they support many species of animals, some of which require specific habitats and linkages to other terrestrial or marine habitats, and (iii) they exist and evolve within dynamic coastal settings, subject to changing tidal levels, salinities and long term forcing factors associated with sea-level rise and climate change.
The littoral mudflat habitat is naturally resilient and can recuperate well from isolated physical and chemical disturbances, although they have been considered to be very sensitive to oil pollution as the oil enters lower layers of the mudflats where lack of oxygen prevents decomposition of the oil. Once the habitat disappears, due to agricultural land reclaim, infrastructure development or saltmarsh growth, the process is generally irreversible although since the 1980s there have been some intertidal habitat creation or restoration schemes (de-polderisation or managed retreat).

Trends in extent

Average current trend in quantity

Stable Stable
EU28 EU28+

Trends in quality

Average current trend in quality

Stable Stable
EU28 EU28+

Conservation and management needs

Management of both terrestrial and marine activities will be important to control factors leading to the decline and threats to this habitat. The water quality on mudflats is regulated by a number of EC Directives including the the Urban Waste Water Treatment Directive, the Nitrates Directive and the Water Framework Directive. These commitments provide for the regulation of discharges to the sea and have set targets and quality standards covering many metals and pesticides, and other toxic persistent and bioaccumulative substances.
The designation of protected areas and management schemes has led to the introduction of measures to protect or improve the quality of this habitat. The largest of these, agreed by the governments of the Netherlands, Germany and Denmark is the trilateral Wadden Sea Plan. Other management measures include the regulation of dredging, coastal developmet, aquaculture, hard coastal defence structures and the control of invasive species such as the cordgrass Spartina anglica and the Pacific oyster Crassostrea gigas.

List of conservation and management needs

  • Measures related to agriculture and open habitats
    • Other agriculture-related measures
  • Measures related to wetland, freshwater and coastal habitats
    • Other wetland related measures
    • Restoring/Improving water quality
    • Restoring/Improving the hydrological regime
    • Restoring coastal areas
  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Other marine-related measures
    • Establish protected areas/sites
    • Legal protection of habitats and species
    • Manage landscape features
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems
  • Measures related to urban areas, industry, energy and transport
    • Urban and industrial waste management
  • Measures related to special resouce use
    • Regulating/Managing exploitation of natural resources on sea

Distribution

For each habitat a distribution map was produced from a wide variety of sources indicating known and potential occurrences of the habitat in 10x10 km grids within Europe. Occurrences in grid cells were given in two classes: actual distribution from relatively reliable sources (surveys, expert knowledge), and potential distribution based on models or less reliable indicators. Please download the fact sheet to see the map.

Geographic occurrence and trends

Seas Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Bay of Biscay and the Iberian Coast Present Unknown Stable Stable
Celtic Seas
Greater North Sea

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 102,147 71 Unknown EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.
EU28+ >71 Unknown EOO and AOO have been calculated on the available data. Although this data set is known to be incomplete the figures exceed the thresholds for threatened status.
AOO = the area occupied by a habitat measured in number of 10x10 km grid cells.
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).

Characteristic species

The full list of characteristic species and genus are available above from the Summary. The species available in the EUNIS database are shown here.
Invertebrates Abra tenuis
Invertebrates Arenicola marina
Invertebrates Capitella capitata
Invertebrates Cerastoderma edule
Invertebrates Corophium volutator
Invertebrates Crangon crangon
Invertebrates Ensis directus
Invertebrates Eteone longa
Invertebrates Gammarus locusta
Invertebrates Heteromastus filiformis
Invertebrates Hydrobia ulvae
Invertebrates Lanice conchilega
Invertebrates Macoma balthica
Invertebrates Mya arenaria
Invertebrates Mytilus edulis
Invertebrates Nereis diversicolor
Invertebrates Phyllodoce mucosa
Invertebrates Pygospio elegans
Invertebrates Retusa obtusa
Invertebrates Scoloplos armiger
Species scientific name English common name Species group
Abra tenuis Invertebrates
Arenicola marina Invertebrates
Capitella capitata Invertebrates
Cerastoderma edule Invertebrates
Corophium volutator Invertebrates
Crangon crangon Invertebrates
Ensis directus Invertebrates
Eteone longa Invertebrates
Gammarus locusta Invertebrates
Heteromastus filiformis Invertebrates
Hydrobia ulvae Invertebrates
Lanice conchilega Invertebrates
Macoma balthica Invertebrates
Mya arenaria Invertebrates
Mytilus edulis Invertebrates
Nereis diversicolor Invertebrates
Phyllodoce mucosa Invertebrates
Pygospio elegans Invertebrates
Retusa obtusa Invertebrates
Scoloplos armiger Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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Denmark
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