Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA2.32 Polychaete/ oligochaete-dominated upper estuarine Atlantic littoral mud

Polychaete/ oligochaete-dominated upper estuarine Atlantic littoral mud

Quick facts

Red List habitat type code NEAA2.32
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)


Upper estuarine sandy mud and muddy shore communities, in areas with significant freshwater influence. The littoral mud typically forms mudflats, though dry compacted mud can form steep and even vertical structures, particularly at the top of the shore adjacent to saltmarshes. Little oxygen penetrates these cohesive sediments, and an anoxic layer is often present within millimetres of the sediment surface.

The upper estuarine mud communities support few infaunal species and are principally characterised by a restricted range of polychaetes and oligochaetes. There are three oligochaete dominated upper estuarine mud biotopes associated with this habitat. Of these three, the biotope characterised by Nephtys hombergii and Streblospio shrubsolii  occurs the furthest towards the mid estuary, and possibly lower on the shore than the other two. The biotope characterised by Tubificoides benedii and other is the most extreme upper estuarine biotope, occurring at the head of estuaries where there is no strong river flow and hence conditions are very sheltered, and there is a very strong freshwater influence. Further towards the mid estuary, this biotope may occur at the top of the shore.

Indicators of quality:

Many indicators of quality have been used for this habitat with particular parameters 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. Indicators of quality of this habitat are frequently linked to those for the whole estuarine environment and therefore include morphological and physical characteristics, carrying capacity and water quality parameters. For the mudflat itself benthic indices, contaminant levels and productivity are some of the frequently used measures of quality.

Indices developed to assess the ecological status of coastal waters, including estuaries, according to the Water Framework Directive, include physical indicators, water quality indicators and measures of benthic diversity, species richness and abundance. The latter group, which is particularly relevant to benthic habitats, includes a Benthic Quality Index, an Infaunal Trophic Index, a Marine Biotic index based on ecological groups, and the Benthic Opportunistic Polychaetes/Amphipods index.

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

Threat status

Synthesis of Red List assessment

Historically, estuarine mudflats have suffered considerable declines in extent as a result of human activity. Whilst this no longer takes place on the scale practiced several centuries ago, piecemeal loss of areas of estuarine mudflat continues to occur. Declines in abiotic and biotic quality have also taken place, for example as a result of the discharge of industrial effluents and nutrient enrichment due to run-off from surrounding land, and this remains an issue in some estuaries.
Because of the very substantial historical loss in quantity of this habitat, expert opinion is that this habitat should be assessed as Endangered under criterion A3 for both the EU 28 andEU 28+.
Red List Category Red List Criteria
Endangered A3
Red List Category Red List Criteria
Endangered A3

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Urbanisation, residential and commercial development
    • Discharges
    • Disposal of industrial waste
  • Biological resource use other than agriculture & forestry
    • Fishing and harvesting aquatic resources
    • Bait digging / Collection
  • Pollution
    • Marine water pollution
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Landfill, land reclamation and drying out, general
    • Removal of sediments (mud...)
    • Modification of hydrographic functioning, general
    • Siltation rate changes, dumping, depositing of dredged deposits
    • Dykes, embankments, artificial beaches, general
  • Climate change
    • Changes in abiotic conditions
    • Flooding and rising precipitations
    • Water flow changes (limnic, tidal and oceanic)
    • Wave exposure changes
    • Sea-level changes
    • Changes in biotic conditions
    • Habitat shifting and alteration

Habitat restoration potential

Where the soft sediment habitat is no longer present restoration may be possible but involve substantive works. Some examples are the depolderisation projects and restoration schemes on Elbe, Wesser, Scheldt, and Humber through sediment management, allowing development of natural tidal floodplains, and set back/managed realingment/depolderisation to restore intertidal mudflats within estuaries.

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 of quantity and quality of this habitat. Integrated Coastal Zone Management which includes spatial planning measures and limits land claim and other activities that alter the tidal regime in the upper reaches of estuaries are examples of beneficial measures. Other include the regulation of dredging, of coastal development, aquaculture, hard coastal defence structures and the control of invasive species
The water quality on mudflats has been 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. National schemes, such as the Aquatic National Monitoring Programme in Denmark, provide data to indicate progress with implementation of such Directives.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
    • Restoring/Improving the hydrological regime
  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Establish protected areas/sites
  • 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


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 271,876 106 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+ >106 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.
Algae Ulva lactuca
Invertebrates Corophium volutator
Invertebrates Hydrobia ulvae
Invertebrates Nephtys hombergii
Invertebrates Scrobicularia plana
Invertebrates Streblospio shrubsolii
Invertebrates Tubificoides benedii
Species scientific name English common name Species group
Ulva lactuca Algae
Corophium volutator Invertebrates
Hydrobia ulvae Invertebrates
Nephtys hombergii Invertebrates
Scrobicularia plana Invertebrates
Streblospio shrubsolii Invertebrates
Tubificoides benedii Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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1050 Copenhagen K
Phone: +45 3336 7100