Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA5.6w Mediterranean infralittoral oyster beds

Mediterranean infralittoral oyster beds

Quick facts

Red List habitat type code MEDA5.6w
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)


Infralittoral oyster beds on rocky and soft bottoms comprised mainly by the European flat oyster Ostrea edulis with densities of 5 or more per m2. The oysters cement themself to the substratum and can form a dense cover. They may be found as individuals or clusters attached to rock surfaces, on other shelled animals like the endemic noble shell (Pinna nobilis) or on coarse sandy bottoms. The diet of oysters consists of phytoplankton and detritus filtered from the surrounding water. More frequently they can be found close to river mouth areas or estuaries and sheltered bays. There are three distinct habitat components; the interstices within the oyster matrix; the biodeposits beneath the bed; and the substratum afforded by the oyster shells themselves. A diverse range of epibiota and infauna often exists in these parts of the habitat.

Indicators of quality:

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include the presence of particular species, water quality parameters, levels of exposure to a particular exposure as well as more integrated indices which describe habitat function and structure, such as trophic index, or successful stages of development in habitats that have a natural cycle of change over time.

There are no known commonly agreed indicators of quality for this habitat, although particular parameters may be set in certain situations, e.g. protected features with Natura 2000 sites, where reference values may have been determined and applied on a location-specific basis. Presence and abundance of the oyster will be a key indicator of this habitat.

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

Threat status

Synthesis of Red List assessment

This habitat has a widespread distribution in the Mediterranean but is thought to only be present in the EU 28. There is a lack of quantifiable date on trends in the extent and quality of this habitat however it is known to have declined very significantly since the last century. Although there are significant data deficiencies, expert opinion is that this habtiat should be assessed as Endangered for both the EU 28 and EU 28+ on the basis of historical decline.
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

  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Fishing and harvesting aquatic resources
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Marine water pollution
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Climate change
    • Changes in abiotic conditions
    • Changes in biotic conditions

Habitat restoration potential

Recovery times from over exploitation and other causes of damage have been estimated to take up to 20 years.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

The remaining natural beds are very few, scattered through the European Mediterranean countries. Whenever these are exploited, this has to be regulated through intervention measures (changes in the extent and amount of the extracted oysters per year or bans on extraction for a long period). Detailed mapping of the extent of the natural mussel beds is lacking and should be a priority for the countries that host 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
    • Restoring marine habitats
  • Measures related to spatial planning
    • Establish protected areas/sites
    • Legal protection of habitats and species
  • 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
  • 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)
Adriatic Sea Present Unknown Decreasing Decreasing
Aegian-Levantine Sea
Ionian Sea and the Central Mediterranean Sea
Western Mediterranean 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 1,411,607 212 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+ 212 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

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Phone: +45 3336 7100