Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA5.6z Circalittoral biogenic habitats in the Mediterranean - oyster beds

Circalittoral biogenic habitats in the Mediterranean - oyster beds

Quick facts

Red List habitat type code MEDA5.6z
Threat status
Europe Data Deficient
EU Data Deficient
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


Circalittoral oyster beds on rocky and soft bottoms comprised mainly by the Neopycnodonte cochlear. These make large mass aggregations on the bottom and support the development of other life forms such as cnidarians, bryozoans and sponges. In the Mediterranean, two species of the genus Neopycnodonte exists. Neopycnodonte cochlear and Neopycnodonte zibrowii. N. cochlear is found in waters with depths of 40-400 meters while N. zibrowii is found in deeper waters and so not included further in this assessment. This habitat  can also be found in underwater caves, in even shallow waters, indicating that the dim light is the modulator of the distribution. In the circallitoral zone, N. cochlear can cover large areas of the bottom, both muddy and rocky. Often, shells can be found growing on disgarded fishing gears, when fleets use to fish in areas where deepsea oyster exists. 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, density and size range of the oyster N. cochlear can be used as an indicator of quality.

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

Threat status

Synthesis of Red List assessment

This circalittoral biogenic habitats has not been studied in any detail in the Mediterranean. Much is unknown about its spatial extent, biotic/abiotic characteristics and associated biodiversity. There is also a lack of information regarding trends. This habitat has therefore been assessed as Data Deficient for both the EU 28 and EU 28+.
Red List Category Red List Criteria
Data Deficient -
Red List Category Red List Criteria
Data Deficient -

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Mining, extraction of materials and energy production
    • Exploration and extraction of oil or gas
    • Production drilling
    • Jack-up drilling rig
    • Drill ship
  • Biological resource use other than agriculture & forestry
    • Professional active fishing
    • Benthic or demersal trawling
  • Pollution
    • Marine water pollution
  • Invasive, other problematic species and genes
    • Invasive non-native species

Habitat restoration potential


Trends in extent

Average current trend in quantity

Unknown Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
EU28 EU28+

Conservation and management needs

Important measures for the protection of this habitat should start with the identification and mapping of the beds. Up to now, the knowledge of these beds comes from oceanographic cruises that collect benthic samples in specific locations (stations), from bycatch of the benthic trawls and artisanal fisheries as well as from information that is provided by museum collection and shell collectors. Management of demersal fisheries, including the establishment of protected areas, regulation of oil and gas licencing and disposal activities to avoid these habitats will be beneficial.

List of conservation and management needs

  • Measures related to spatial planning
    • Establish protected areas/sites
    • Establishing wilderness areas/allowing succession
    • 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 Unknown Unknown
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 Unknown Unknown Unknown This habitat is present in all the sub-basins and is common. EOO and AOO are considered likely to exceed the thresholds for a threatened category on the basis of restricted geographic distribution alt
EU28+ Unknown Unknown This habitat is present in all the sub-basins and is common. EOO and AOO are considered likely to exceed the thresholds for a threatened category on the basis of restricted geographic distribution alt
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 Neopycnodonte cochlear
Species scientific name English common name Species group
Neopycnodonte cochlear Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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