Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA5.37 Atlantic lower circalittoral mud

Atlantic lower circalittoral mud

Quick facts

Red List habitat type code NEAA5.37
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)


In mud and cohesive sandy mud in the offshore circalittoral zone, typically below 50-70m, a variety of faunal communities may develop, depending upon the level of silt/clay and organic matter in the sediment. The relatively stable conditions associated with deep mud habitats often lead to the establishment of communities of burrowing megafaunal species where bathyal species may occur together with coastal species. The burrowing megafaunal species include burrowing crustaceans such as Nephrops norvegicus and Callianassa subterranea. The mud habitats in deep water can also support seapen populations and communities with Amphiura spp. The bioturbating activities of the infauna present in these biotopes are particularly important in controlling chemical, physical and biological processes, especially when the influences of physical disturbances such as wave action or strong currents are minimised (owing to their depth). The presence of burrowing fauna such as polychaetes significantly influence nutrient fluxes of nitrogen and phosphorus at the sediment-water interface, as their burrowing activity promotes oxygenation of the substrata. The organisms in these biotopes, particularly polychaetes and foraminiferans, are an important food source for higher trophic levels, particularly demersal fish and other benthic macrofauna. As such, the species characteristic of this habitat represent an important bentho-pelagic link increasing the overall biodiversity and ecological value of the habitat.

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. Examples of indicators of damage and naturalness have been proposed for offshore deep sea muds include; the presence of typical benthic invertebrate communities and other large burrowing megafauna, the sediment composition or sedimentation rates/disturbance, the presence of the climax community including crustacean and polychaetes populations, and an absence of Beggiatoa mats. A reduction in the abundance of less sessile and fragile species and an increase in more carnivorous and scavenging species are potential indicators of disturbance.

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 deep basins as well as deep sheltered inlets. There are well known extensive and well-developed deep water mud basins in the North East Atlantic in the Kattegat, the Grand Vasiere off Gascony, France and to the west of Ireland. This habitat is also present in deep, sheltered inlets such as some of the Scottish sea lochs. Some declines in habitat quantity (as a result of shifts to different sediment composition) have been recorded and there are many well documented examples of decline in quality.
Most sedimentary benthic systems of the continental shelf of Europe have been modified by fishing activity in the last 100 years, particularly by mobile demersal gears, and this remains a significant pressure. Disturbance of the substratum due to intensive fishing activities using bottom trawls or dredges can damage or modify infaunal communities, with burrowing echinoderms and bivalves being particularly vulnerable.research suggests that some gears may also be modifying the biogeochemistry of the sediments by affecting organic matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth. Analysis by ICES (for the period 2009-2012) shows considerable overlap of this habitat with fishing intensity by gears which are known to have damaging effects on the epifauna and shallow infauna. More recent data for a single year (2013/2014) have revealed that more than 95% of modelled area of deep circalittoral mud across in the North Sea and Celtic Sea is considered to have been subject to fishing pressure by EU trawlers (bottom otter, beam and mid-water trawls) and that more than 80% of the deep circalittoral mud habitat across the North East Atlantic shelf area has been subject to abrasion disturbance. There are also regional studies, such as in the Kattegat, which show a similar pattern of overlap of this habitat type with the use of bottom gears that are known to alter the quality and take place at a frequency which maintains a disturbed condition. Much the same footprint of activity is likely each year and as this type of fishing pressure has been ongoing for many decades, there has most likely been a cumulative impact on habitat quality. Signficant effects have been observed in response to long-term chronic disturbance from otter trawling, for example, with negative effects on benthic infauna abundance, biomass and species richness with clear changes in community composition that may have far-reaching implications for the integrity of marine food webs.
Expert opinion is that there has been a very substantial reduction in quality of this habitat, most likely an intermediate decline affecting more than 80% of its extent although it is clear that in some locations there has also been a severe decline. The severity will depend on factors such as the intensity and frequency of disturbance. This habitat has therefore been assessed as Endangered for both the EU 28 and EU 28+ because of both past and likely continuing declines in quality.
Red List Category Red List Criteria
Endangered C/D1
Red List Category Red List Criteria
Endangered 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
    • Fishing and harvesting aquatic resources
    • Professional active fishing
    • Benthic or demersal trawling
    • Demersal seining
    • Benthic dredging
  • 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. Free living species are also likely to recolonise areas more quicky that those that grow attached to the substratum and have an erect or stalked body form such as seapens. Recovery times of communities in deep circalittoral mud habitats following oxygen depletion and pollution has been investigated in several studies of the Gullmarsfjord, Sweden where they reported to be between 2-8 years.
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

The regulation of the use of fishing gears that damage or disturb seabed communities is key to the conservation of this habitat. This may be achieved by spatial and temporal controls as well as gear design and deployment regulations using fisheries management measures as well as conservation legislation in marine protected areas. Identification in Biodiversity Action Plans (e.g. as priority features) is also being used to raise awareness of pressures and threats to this habitat and the need for conservation measures.

List of conservation and management needs

  • 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
  • Measures related to special resouce use
    • Regulating/Managing exploitation of natural resources on sea


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 64,816 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 2,576,337 1,868 >64,816 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+ >1,868 >64,816 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

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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1050 Copenhagen K
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