Communities of Atlantic circalittoral caves and overhangs

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. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats