Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA5.34 Marine Atlantic infralittoral fine mud

Marine Atlantic infralittoral fine mud

Quick facts

Red List habitat type code NEAA5.34
Threat status
Europe Near Threatened
EU Near Threatened
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


Shallow sublittoral muds, extending from the extreme lower shore to about 15-20 m depth in fully marine or near marine conditions, predominantly in extremely sheltered areas with very weak tidal currents. Such habitats are found in sealochs and some rias and harbours. In very shallow extremely sheltered very soft muds the lugworm Arenicola marina may form very conspicuous mounds and casts. At such sites, high densities of synaptid holothurians such as Labidoplax media and Leptosynapta bergensis occur. The sediment surfaces may become covered by a diatom film at certain times of the year. Mobile species are opportunistic scavengers and predators and include starfish (e.g. Asterias rubens), crabs and hermit crabs (e.g. Carcinus maenas and Pagurus bernhardus), flatfish and gobies (e.g. Pomatoschistus minutus). 

Sheltered sediments such as these are characterized by fine grain size, low porosity, generally low permeability (and hence high water content), high sediment stability (due to cohesion), a low oxygen content and highly reducing conditions. The mud surface is oxygenated. However, in fine muds, the anoxic reducing layer is likely to be very close to the surface, often less than 1cm. Bioturbation by burrowing species, results in mobilisation of the sediment and nutrients from deeper sediment to the surface, making nutrients available to surface dwelling organisms. In addition, continued irrigation of their burrows by Arenicola marina and Leptosynata sp. transports oxygenated water into the sediment, resulting in oxygenated micro-environments in the vicinity of their burrows.

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 indiceswhich 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. Key driving influences and output processes of shallow sublittoral mud habitats that are likely to be sensitive to pressures and may be useful for monitoring to identify anthropogenic causes of change include habitat structure changes, removal of particular species such as those which are key in bioturbation and biodeposition, or nutrient and biogeochemical cycling, changes in siltation rates and organic enrichment.

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

Threat status

Synthesis of Red List assessment

This habitat is present across the region in shallow basins and sheltered inlets. There are no precise figures on its extent of however a combination of survey data and modelling indicates that it cannot be considered to have a restricted geographical distribution nor to occur in only a few locations in the North East Atlantic. Expert opinion is that there has been a decline in quality as exemplified by changes in species composition. There is a lack of comprehensive data however, expert opinion is that this habitat should be assesssed as Near Threatened for both the EU 28 and EU 28+ because of both past and likely future declines in quality.
Red List Category Red List Criteria
Near Threatened C/D1
Red List Category Red List Criteria
Near Threatened C/D1

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Urbanisation, residential and commercial development
    • Discharges
  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Fishing and harvesting aquatic resources
    • Professional active fishing
    • Benthic or demersal trawling
  • Pollution
    • Nutrient enrichment (N, P, organic matter)
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Modification of hydrographic functioning, general

Habitat restoration potential

Timescale between incidents of damaging activity, the type of damaging activity and the predominant species, influences recovery. Studies have shown that recovery times following dredging were significantly shorter for short-lived species (<1 – 3 years), free-living and tube-dwelling species and for scavenging or opportunistic species, than for medium-lived species (3 – 10 years), burrow-dwelling species and suspension feeders. In trawled areas, recovery times were significantly shorter for free-living species, species covered by an exoskeleton or a hard tunic and species that produce pelagic or benthic eggs than for epiphytic/zoic species, species that grow attached to the substratum and have an erect or stalked body form, and species that reproduce asexually. Areas with high levels of natural disturbance have community compositions and functions that are more resilient than those found in areas with less natural disturbance.
Recovery times following oxygen depletion and pollution has been investigated in several studies of the Gullmarsfjord, Sweden and reported to be between 2-8 years. Isolation is also a factor. Recruitment to isolated habitats, such as sea lochs, from outside the area may take some time and be dependant on sporadic events such as storms.
Differences in the recoverability of different species groups following fishing may result in changes in community composition and ecosystem functioning over the long term.

Trends in extent

Average current trend in quantity

Unknown Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

This habitat can benefit from the regulation of the use of fishing gears that damage or disturb seabed communities. This may be achieved by spatial and temporal controls as well as gear design and deployment using fisheries management measures as well as conservation legislation in marine protected areas. Spatial planning (including zoning) can be used to address potential threats from dredging, coastal development, and fish farming. The regulation of discharges and run off from agricultural land to the marine environment can be used to avoid eutrophication effects associated with nutrient enrichment.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Other marine-related measures
    • Establish protected areas/sites
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems


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 Decreasing Unknown
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 2,738.38 183 >710 The area estimate for this habitat has been derived from a synthesis of EUNIS seabed habitat geospatial information for the European Seas but is recognised as being an underestimate.
EU28+ >183 >710 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.
Fishes Pomatoschistus minutus
Invertebrates Abra nitida
Invertebrates Aphelochaeta marioni
Invertebrates Arenicola marina
Invertebrates Asterias rubens
Invertebrates Carcinus maenas
Invertebrates Cerastoderma edule
Invertebrates Hydrobia ulvae
Invertebrates Leptosynapta bergensis
Invertebrates Liocarcinus depurator
Invertebrates Ocnus planci
Invertebrates Ophiodromus flexuosus
Invertebrates Pagurus bernhardus
Invertebrates Philine aperta
Invertebrates Virgularia mirabilis
Species scientific name English common name Species group
Pomatoschistus minutus Common goby Fishes
Abra nitida Invertebrates
Aphelochaeta marioni Invertebrates
Arenicola marina Invertebrates
Asterias rubens Invertebrates
Carcinus maenas Invertebrates
Cerastoderma edule Invertebrates
Hydrobia ulvae Invertebrates
Leptosynapta bergensis Invertebrates
Liocarcinus depurator Invertebrates
Ocnus planci Invertebrates
Ophiodromus flexuosus Invertebrates
Pagurus bernhardus Invertebrates
Philine aperta Invertebrates
Virgularia mirabilis Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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