Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA5.62 Mussel beds (Mytilus edulis) on Atlantic sublittoral sediment

Mussel beds (Mytilus edulis) on Atlantic sublittoral sediment

Quick facts

Red List habitat type code NEAA5.62
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)

Summary

Sublittoral mussel beds of the common mussel Mytilus edulis may be sublittoral extensions of littoral reefs or exist independently. They beds are found in a variety of situations ranging from sheltered estuaries and marine inlets to open coasts and offshore areas, in fully marine or sometimes variable salinity conditions in the outer regions of estuaries. They may occupy a range of substrata, although due to the accumulating and stabilising effect such communities have on the substratum muddy mixed sediments are typical. There are three distinct  habitat components: the interstices withn the mussel matrix; the biodeposits beneath the bed; and the substratum afforded by the mussel shells themselves. 

All three components often contain a diverse range of epibiota and infauna. The mussel matrix may support sea cucumbers, anemones, boring clionid sponges, ascidians, crabs, nemerteans, errant polychaetes and flatworms. The biodeposits attract infauna such as sediment dwelling sipunculids, oligochaetes, and polychaetes while epizoans may use the mussels shells themselves as substrata.

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.

The overall quality and continued occurrence of this habitat is, however, largely dependent on the presence of Mytilus edulis which creates the biogenic structural complexity on which the characteristic associated communities depend. The density and the maintenance of a viable population of this species is a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. Monitoring programmes may include measures of biomass, coverage, length frequency distribution, a condition index for the mussels (a ratio between biomass versus shell length) and descriptions of the structure of a bed including vertical height profile, thickness and type of accumulated sediment, coverage and biomass of macroalgae.

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

Threat status

Synthesis of Red List assessment

This habitat has a wide geographical distribution and is not limited to a few locations. Trends can be difficult to distinguish as there can be very large annual variations influenced by the success of spatfalls, and weather conditions such as storm events and starfish predation which can rapidly wipe out subtidal mussel beds. An analysis of trends in this habitat should distinguish between naturally occurring and cultivated beds but data are typically from the latter which are commercially exploited.
Given the reported decrease in recruitment (spat falls) across Europe since the 1980s and that the largest extent of this habitat is in the southern North Sea where there have been substantial losses, the data suggest that overall the extent of this habitat is decreasing.
This habitat has declined in quality in some parts of its range over the last 50 years but the overall situation is unclear. For example, there has been an extremely heavy impact on spat from commercial fishing which decreases habitat structure and density directly, and also causes changes in the species composition to include the non-native oyster (C.gigas), Ensis, Mya and Marenzelleria, but this is not the case throughout the range of this habitat in the North East Atlantic region.
The overall assessment is that this habitat is Near Threatened for both the EU 28 and EU 28+ on the basis of decline in quantity over the last 50 years.
EU
Red List Category Red List Criteria
Near Threatened A1
Europe
Red List Category Red List Criteria
Near Threatened A1

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Fishing and harvesting aquatic resources
    • Professional active fishing
    • Benthic or demersal trawling
  • Human intrusions and disturbances
    • Other human intrusions and disturbances
    • Shallow surface abrasion/ Mechanical damage to seabed surface
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Climate change
    • Changes in biotic conditions

Habitat restoration potential

There is a good capacity for this habitat to recover following damage. The time taken will depend on the occurence and frequency of good spatfalls and natural events such as storm damage and the presence of predators.
Blue mussels are sessile, attached organisms that are unable to repair significant damage to individuals. They do not reproduce asexually and therefore the only mechanism for recovery from significant impacts is larval recruitment to the bed or the area where previously a bed existed. Recruitment is often sporadic, occurring in unpredictable pulses, but persistent mussel beds can be maintained by sporadic or relatively low levels of recruitment.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
EU28 EU28+

Conservation and management needs

Management of the wild commercial mussel fishery is key to the conservation of this habitat. This includes controls on the removal of seed stock, the level of fishing effort and locations where fisheries are permitted. In the Netherlands and Germany efforts are also underway to switch from collection of spat by dredging to use of seed collectors (ropes, nets, poles), with the aim of eliminating the bottom fishery within the next 10 years. In France and Spain the use of seed collectors has been standard practice for decades. Closures of collecting areas to enable recovery of stocks and the associated habitat are also needed, as well as regulation of discharges to the marine environment which result in nutrient enrichment that affects the condition and viability of this habitat.

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 hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems
    • Specific single species or species group management measures

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 Unknown Decreasing
Celtic Seas
Kattegat
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 560,102 90 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+ >90 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 Asterias rubens
Invertebrates Buccinum undatum
Invertebrates Cancer pagurus
Invertebrates Carcinus maenas
Invertebrates Cereus pedunculatus
Invertebrates Gammarus salinus
Invertebrates Heteromastus filiformis
Invertebrates Kefersteinia cirrata
Invertebrates Kirchenpaueria pinnata
Invertebrates Maja squinado
Invertebrates Molgula manhattensis
Invertebrates Mytilus edulis
Invertebrates Necora puber
Invertebrates Nucella lapillus
Invertebrates Sagartiogeton undatus
Invertebrates Sertularia argentea
Invertebrates Tubularia indivisa
Invertebrates Urticina felina
Species scientific name English common name Species group
Asterias rubens Invertebrates
Buccinum undatum Invertebrates
Cancer pagurus Invertebrates
Carcinus maenas Invertebrates
Cereus pedunculatus Invertebrates
Gammarus salinus Invertebrates
Heteromastus filiformis Invertebrates
Kefersteinia cirrata Invertebrates
Kirchenpaueria pinnata Invertebrates
Maja squinado Invertebrates
Molgula manhattensis Invertebrates
Mytilus edulis Invertebrates
Necora puber Invertebrates
Nucella lapillus Dog whelk Invertebrates
Sagartiogeton undatus Invertebrates
Sertularia argentea Invertebrates
Tubularia indivisa Invertebrates
Urticina felina Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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