Mussel beds (Mytilus edulis) on Atlantic sublittoral sediment
|Red List habitat type||code NEAA5.62|
|Source||European Red List habitat factsheet|
|European Red List of habitats reports|
|European Red List of habitats (Excel table)|
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.
Synthesis of Red List assessment
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.
|Red List Category||Red List Criteria|
|Red List Category||Red List Criteria|
Confidence in the assessment
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
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
Trends in quality
Average current trend in quality
Conservation and management needs
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
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|
|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.|
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).
|Species scientific name||English common name||Species group|
|Nucella lapillus||Dog whelk||Invertebrates|
Relation to other habitat types mentioned in legal instruments
|Legal text||Annex||Name in legal text||Code in legal text||
|Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora - consolidated version 01/01/2007||Annex I: natural habitat types of community interest whose conservation requires the designation of special areas of conservation||Reefs||1170||Narrower||http://ec.europa.eu/environm...rective/index_en.htm|