Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA1.44 Communities of Mediterranean mediolittoral caves and overhangs

Communities of Mediterranean mediolittoral caves and overhangs

Quick facts

Red List habitat type code MEDA1.44
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)


Mediolittoral caves and overhangs are a special habitat whose main distinctive trait is the low irradiance. The habitat can be found on most rocky shores regardless of wave exposure. The shaded nature of caves and overhangs diminishes the amount of desiccation suffered by biota during periods of low tides which allows certain species to proliferate.

Algal growth is restricted to a very few species that can withstand low light levels, low to high hydrodynamism, and extended periods of desiccation. Canopy-forming macroalgae are absent whilst encrusting rhodophytes are dominant. Some variation in the species composition of the individual caves must be expected depending on local conditions although in general the communities are very poor in species. At the entrance to mediolittoral caves where there is sufficient light red algae may be present, particularly an association of non‐calcified encrusting red algae Hildenbrandia rubra and Phymatholithon lenormandii, under the red alga Lithophyllum byssoides.

In general, the biomass and diversity of algal species found in upper and mid‐shore littoral caves decreases with increasing depth into the cave as the light levels diminish. Fauna usually only occur on the lower and mid-level walls of the caves and generally comprise barnacles, anemones and tube‐forming polychaetes.

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.

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. It is present within Marine Protected Areas but accurate numbers and the ecological status of these caves is generally unknown. Localised studies have been conducted at different sites mostly in the Western Mediterranean, but the earliest data were only published in 1940-50. Consequently, there is a lack of quantiative data on trends although expert opinion is that habitat quality has most likely decreased in response to pressures such as habitat destruction associated with coastal development
This habitat has a large EOO and AOO, and therefore qualifies as Least Concern under criterion B. However the habitat is assessed as Data Deficient both at the EU 28 and EU 28+ levels because of a lack of information on any trends in quantity and quality.
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

  • Transportation and service corridors
    • Marine constructions
  • Urbanisation, residential and commercial development
    • Urbanised areas, human habitation
    • Discharges
  • Human intrusions and disturbances
    • Speleology
    • Recreational cave visits
    • Scubadiving, snorkelling
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Marine macro-pollution (i.e. plastic bags, styrofoam)
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Climate change
    • Temperature changes (e.g. rise of temperature & extremes)
    • Sea-level changes

Habitat restoration potential

The habitat might be able to recover to certain environmental stresses, however depending of the factor it might not be able to recover easily or no at all (e.g. when invaded by invasive algae or when building works take place in the surrounding area).

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

Marine cave habitats are protected by the EU Habitats Directive (92/43/EEC) under the name “Submerged or partially submerged sea caves” (Habitat code 8330). Semidark and dark cave communities have been included in two Action Plans by UNEP-MAP-RAC/SPA (2008 and 2015 respectively), adopted by contracting parties of the Barcelona Convention specifically aiming at their conservation. An evaluation on Mediterranean MPA in 2008 has shown that around 56% of the Mediterranean MPAs include marine caves although, the accurate number of marine caves within designated MPAs remains unknown.
The creation of a Marine Caves' Register at the country level with an assement of their ecological status, adequate regulations to protect these environments and further research to understand its diversity and function are recommended.

List of conservation and management needs

  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Other marine-related measures
    • Establish protected areas/sites
    • Legal protection of habitats and species


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 76,721 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 2,208,454 1,063 75,436 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+ 1,519 76,721 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.
Algae Gymnothamnion elegans
Algae Hildenbrandia rubra
Algae Lithophyllum byssoides
Algae Phymatolithon lenormandii
Invertebrates Actinia equina
Invertebrates Chthamalus montagui
Invertebrates Chthamalus stellatus
Invertebrates Ligia italica
Species scientific name English common name Species group
Gymnothamnion elegans Algae
Hildenbrandia rubra Algae
Lithophyllum byssoides Algae
Phymatolithon lenormandii Algae
Actinia equina Invertebrates
Chthamalus montagui Invertebrates
Chthamalus stellatus Invertebrates
Ligia italica Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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