Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA4.71 Communities of Atlantic circalittoral caves and overhangs

Communities of Atlantic circalittoral caves and overhangs

Quick facts

Red List habitat type code NEAA4.71
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)


Caves and overhanging rock in the circalittoral zone, away from significant influence of strong wave action. This habitat generally occurs in open coast waters or on wave sheltered coasts with moderate tidal flow. Caves and overhangs display a wide range of structural and ecological variation, depending on the prevailing physical and geological conditions. Those which have extensive areas of vertical and overhanging rock, and those that extend deeply into the rock, generally support the widest range and highest diversity of species. In the circalittoral zone these are characterised by sponges and anthozoans. Resident, seasonal and occasional species of fish are also present in sublittoral caves. Extensive cave systems, such as the flooded lava tubes in the Canary Islands, may become anchialine at their innermost extents because of the long residence time (months to years) of seawater. In such systems, the extent of saltwater intrusion, its stratification and the residence time of seawater (which can be from months to years) has resulted in a specialised fauna with pronounced morphological, physiological, biochemical and behavioural adaptations, such as the blind crab Munidopsis polymorpha.

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 ma yface; 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 overtime.

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.

Cave biotopes can be broadly divided into those characterised by long lived species and those characterised by ephemeral and scour tolerant species. Long lived species such as cup corals and sponges may be targeted as indicators that a cave system has remained undisturbed. Individuals or individual colonies of such species might represent suitable for monitoring change. 

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

Threat status

Synthesis of Red List assessment

Sublittoral cave systems have not been extensively studied, and those which have been investigated in any detail are generally in shallow waters (diving depths). There are no consistently applied common metrics to describe the 'quantity' of this habitat type, which may include linear extent, volume, depth, wall height and floor width. Caves are highly dynamic and their extent is likely to fluctuate over time, particularly in friable rock where erosion or collapse processes are likely to occur. Because of the lack of quantitative data on extent and condition, no assessment of trends in quantity and quality can be made at the present time. The current Red List assessment for this habitat is therefore 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

  • Human intrusions and disturbances
    • Outdoor sports and leisure activities, recreational activities
    • Scubadiving, snorkelling
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Siltation rate changes, dumping, depositing of dredged deposits

Habitat restoration potential

Caves are highly dynamic and their extent is likely to fluctuate over time, particularly in friable rock where erosion or collapse processes are likely to occur.
Several of the species typically present in this habitat appear to have short-lived benthic larvae, e.g. the soft coral Alcyonium hibernicum which broods planulae larvae that are released at a late development phase and so probably has a short planktonic life. Leptopsammia pruvoti also seems to have short-lived planulae larvae which may settle immediately or very soon after release. In the case of cup corals (Caryophyllia spp. Hoplangia spp.), growth rates are smaller compared to other zoanthids colonising cave walls and roofs.
Sponges are likely to have a longer lived larva and others species, such as the zoanthid anemones Parazoanthus axinellae and Parazoanthus dixoni, reproduce asexually to produce large colonies so may become restablished relatively rapidly if a source population is present and conditions are favourable.

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

There are few conservation and management measures specifically directed at this habitat although some are within designated protected areas. Codes of Conduct which provide guidance on avoiding damage to these habitat are promoted in some areas where cave diving takes place.

List of conservation and management needs

  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Establish protected areas/sites


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 Unknown
Celtic Seas
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 unknown unknown Unknown There is insufficient quantiative data to make an accurate estimate of EOO and AOO however this habitat is widespread.
EU28+ unknown Unknown here is insufficient quantiative data to make an accurate estimate of EOO and AOO however this habitat is widespread.
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