Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA4.71 Communities of Mediterranean circalittoral caves and overhangs

Communities of Mediterranean circalittoral caves and overhangs

Quick facts

Red List habitat type code MEDA4.71
Threat status
Europe Least Concern
EU Least Concern
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

Caves and overhangs constitute typical features of the Mediterranean circalittoral rocky bottoms. They support a great variety of species and host a considerable proportion of the total Mediterranean diversity of certain phyla, such as Brachiopoda, Bryozoa, and Porifera. Several protected and rare species, including recently described species, as well as deep-sea species have been reported. Most of our knowledge comes from caves in the north-west Mediterranean as cave biodiversity is extremely understudied in the southern and eastern basins. They are characterised by high morphological complexity, reflected in abiotic gradients and marked biological zonation along the longitudinal cave axis, from the entrance to the inner cave sectors. Light availability and water confinement are acknowledged as the main driving forces shaping this zonation. Thus, circalittoral caves support a variety of sciaphilic assemblages, usually distributed according to the following scheme: (i) a sciaphilic algae-dominated community at the entrance zone, (ii) a semi-dark zone where sessile filter-feeding invertebrates (mainly sponges and anthozoans) dominate, favored by the disappearance of macroalgae, and (iii) a dark zone which is sparsely colonized by sponges, serpulid polychaetes, bryozoans and brachiopods.

The shift from semi-dark to dark cave communities is evidenced through a sharp decrease in biotic coverage, biomass, three-dimensional biotic complexity, species richness, and the appearance of a black mineral coating of Mn-Fe oxides on the substrate. Additional zones, such as a transitional zone between semi-dark and dark cave communities and an azoic zone at the aphotic cave edge, have been occasionally identified. The limits of these zones might vary among caves with different morphology (e.g. inner zones tend to appear closer to the cave entrance in deeper waters), while in some caves some specific zones might be absent. Semi-dark caves are community is typically dominated by sponges, bryozoans, brachiopods and polychaete species. Serpulid polychaetes (e.g. Protula spp.) can form aggregations, which in some cases constitute the basis for the creation of biogenic structures; these ‘biostalactites’ are constructed by invertebrates (serpulids, sponges, and bryozoans), foraminiferans and carbonate-forming microorganisms. A number of deep-sea species belonging to various taxonomic groups (e.g. sponges, anthozoans and bryozoans) have also been recorded in sublittoral dark caves, regardless of depth

Indicators of quality:

Marine caves are characterised by high levels of individuality and heterogeneity which, coupled to the poor understanding of the ecosystem functioning, make it difficult the assessment of their ecologic quality. However, a number of indicators of quality have been recently suggested for the marine cave ecosystem, such as:

- Presence of invertebrates offering three-dimensional complexity to the substrate, and particularly fragile slow-growing species (e.g. red coral, erect bryozoans)

- High spatial coverage of suspension feeders (i.e. anthozoans) and large filter feeders (e.g. massive sponges)

- Presence of large mysid swarms

- Presence of various omnivorous and carnivorous mobile species (e.g. fish and decapods)

 

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

Threat status

Synthesis of Red List assessment

Little information exists on the overall trends of this habitat. Localised studies have been conducted at different sites mostly in the western Mediterranean Sea, but the earliest data were only published in 1940-50. The lack of historic quantitative and qualitative data on its community structure from most Mediterranean areas constitutes a major impediment to the identification of potential quantity and quality decline of this habitat type through time. However, it can be assumed that the habitat quality might have decreased as a consequence of uncontrolled visitation by SCUBA divers, water temperature rise, marine pollution and habitat destruction. The habitat is known to be widespread throughout the Mediterranean Sea, with a large EOO and AOO, and therefore it qualifies as Least Concern under Criterion B for both the EU 28 and EU 28+.
EU
Red List Category Red List Criteria
Least Concern -
Europe
Red List Category Red List Criteria
Least Concern -

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Urbanisation, residential and commercial development
    • Urbanised areas, human habitation
    • Discharges
  • Human intrusions and disturbances
    • Speleology
    • Recreational cave visits
    • Scubadiving, snorkelling
  • Pollution
    • 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)

Habitat restoration potential

Unknown. Marine caves structures undergo natural cycles through the process of erosion. The associated species are likely to show different restoration capabilities.

Trends in extent

Average current trend in quantity

Unknown Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

Marine cave habitats are a protected feature under EU Habitats Directive (92/43/EEC). Semi-dark 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. A recent evaluation has shown that around 56% of the Mediterranean Marine Protected Areas (MPAs) include marine caves although the precise number of marine caves within designated MPAs remains unknown.
The clear biogeographic patterns exhibited by the Mediterranean marine cave assemblages from different regions suggest the need for protecting marine caves (e.g. management of visitation and other activities) in different regions in order to safeguard representativeness of the habitat type at the Mediterranean scale. Finally, the notable presence of several alien species in southeastern Mediterranean caves (though mostly in semi-submerged and shallow semi-dark caves and tunnels) should be monitored.

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
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems
  • Measures related to special resouce use
    • Regulating/Managing exploitation of natural resources on sea

Distribution

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 Decreasing 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+ 1,094 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.
Fishes Apogon imberbis
Fishes Grammonus ater
Invertebrates Agelas oroides
Invertebrates Argyrotheca cuneata
Invertebrates Axinella damicornis
Invertebrates Caryophyllia inornata
Invertebrates Chondrosia reniformis
Invertebrates Corallium rubrum
Invertebrates Diplastrella bistellata
Invertebrates Haliclona mucosa
Invertebrates Hemimysis margalefi
Invertebrates Hoplangia durotrix
Invertebrates Jaspis johnstoni
Invertebrates Leptopsammia pruvoti
Invertebrates Lithophaga lithophaga
Invertebrates Madracis pharensis
Invertebrates Onychocella marioni
Invertebrates Palinurus elephas
Invertebrates Parazoanthus axinellae
Invertebrates Petrobiona massiliana
Invertebrates Petrosia ficiformis
Invertebrates Phorbas tenacior
Invertebrates Plesionika narval
Invertebrates Polycyathus muellerae
Invertebrates Spirastrella cunctatrix
Invertebrates Stenopus spinosus
Species scientific name English common name Species group
Apogon imberbis Mediterranean cardinalfish Fishes
Grammonus ater Fishes
Agelas oroides Invertebrates
Argyrotheca cuneata Invertebrates
Axinella damicornis Invertebrates
Caryophyllia inornata Invertebrates
Chondrosia reniformis Invertebrates
Corallium rubrum Invertebrates
Diplastrella bistellata Invertebrates
Haliclona mucosa Invertebrates
Hemimysis margalefi Invertebrates
Hoplangia durotrix Invertebrates
Jaspis johnstoni Invertebrates
Leptopsammia pruvoti Invertebrates
Lithophaga lithophaga Invertebrates
Madracis pharensis Invertebrates
Onychocella marioni Invertebrates
Palinurus elephas Invertebrates
Parazoanthus axinellae Invertebrates
Petrobiona massiliana Invertebrates
Petrosia ficiformis Invertebrates
Phorbas tenacior Invertebrates
Plesionika narval Invertebrates
Polycyathus muellerae Invertebrates
Spirastrella cunctatrix Invertebrates
Stenopus spinosus Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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