Red List habitat classification > RL - Marine habitats > RLBLS - Black Sea > BLSA1.4C Communities of Marmara mediolittoral caves and overhangs

Communities of Marmara mediolittoral caves and overhangs

Quick facts

Red List habitat type code BLSA1.4C
Threat status
Europe Data Deficient
EU n/a
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


Oligotrophic waters of sandy plains and rocky substrates (granites, gravel, stones, till, moraines) containing very few minerals. The substrates are covered by a thin layer of detritus. The water is carbon deficient and very poorly buffered (low alkalinity). The water is weakly acid to circumneutral. Concentrations of nitrogen and phosphorus are very low and in the oligotrophic range. The water is clear sometimes humic (brown) but always with a very low concentration of chlorophyll. The vegetation is low in species diversity and dominated by aquatic isoetids, i.e. submerged plants with a small rosette of stiff leaves and an extended root system. Aquatic isoetids are adapted to low carbon availability (low pH) by taking up carbon from the sediment through their extended root system, by an adapted carbon fixation (C4), and by re-using carbon-dioxide produced during respiration. The vegetated layer extends from the littoral to lower parts of the sub-littoral zone. The vegetation and its substrate are mechanically influenced by water movement, ice sheets and wind exposition. Sometimes these oligotrophic water bodies can be almost totally unvegetated. In the temperate, Atlantic zone the characteristic isoetid vegetation occurs in lakes fluctuating in water levels where they may be semi-permanent in the summer periods (Arts, 2002; Dierssen, 1996). Apart from the dominant isoetid aquatic macrophytes (i.e. Isoëtes spp.), other plants may be present in addition (Rørslett & Brettum 1989). Important accompanying isoetid species are Lobelia dortmanna, Subularia aquatica in Northern Europe, Eriocaulon aquaticum in Northern-Atlantic Europe or Luronium natans and Isolepis fluitans in Western Europe zones. Subularia aquatica also extends into the mountainous areas of Iberia in this habitat type (Molina et al., 1999).

Many large lakes in northern Europe represent this type or the more mesotrophic type C1.1b in terms of water chemistry and abundant isoetid vegetation. Occurrence and abundance of other growth forms vary according to shore and bottom material, topography, exposition and fetch. Exposed shores have sparse stands of aquatic vegetation, in sheltered bays vegetation has clear zonation, but the stands are still open (Mäkirinta 1978, Rintanen 1982, Toivonen & Lappalainen 1980). The lower limit of submerged vegetation reaches typically the depth of 3-6 meters, sometimes close to 10 meters. Due to postglacial history deeper lakes host some glacial relict crustaceans and vertebrates, including salmonid fish and a critically endangered fresh water seal (Pusa hispida saimensis). Large lakes have diverse waterfowl populations and are important parts of bird migration routes  Main differences between this habitat type and the C1.1b is that this one is constantly in the oligotrophic range and therefore is generally poorer than C1.1b in species and communities. Indicators of good quality isoetid species are the most characteristic species of this habitat.

The following characteristics may be used as indicators of a favourable quality:

• Large stands of isoetid species;

• Absence or very low abundance of peat mosses;

• Absence or very low abundance of water plants from eutrophic and alkaline waters;

• Low abundance of water plants with other growth forms than the isoetid growth form, e.g. floating or emerged plants e.g. Potamogeton species or Sparganium angustifolium stands or helophytes (Phragmites australis, Eleocharis spp., Equisetum fluviatile, Carex spp.);

• Long-term habitat stability, with no rapid successional trends (e.g. no trends in acidification or eutrophication);

• Low concentrations of nutrients and chlorophyll (approximately P < 15 μg/L and chlorophyll < 3 μg/L.);

• pH weakly acid to circumneutral ( pH 5.5 - 7), alkalinity < 0.5 meq/L. (Note: Chemical and physical parameters are only indicative, they may change in different geographical area and climatic conditions).

• Thin layer of detritus (no accumulation of organic mud);

• No/ little impact from acidification or regulation;

• Absence or very low abundance of submerged or floating mats of macrophytes e.g. Juncus bulbosus;

• Occurrence of conspicuous populations of salmonid fish, but population of roach (Rutilus rutilus) and other Cyprinidae low.

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

Threat status

Synthesis of Red List assessment

The average decline in quality over the last 50 years results in the category Near Threatened (NT) both in the EU28 and EU28+. Besides, the future trend in quality, roughly based on expert opinion, leads to a Near Threatened category for EU28 and EU28+. The average trend in area was only slightly negative, not leading to any Red List category, but it varied strongly between countries.
Red List Category Red List Criteria
n/a C/D1, C/D2
Red List Category Red List Criteria
Data Deficient C/D1, C/D2

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Agriculture
    • Cultivation
    • Modification of cultivation practices
    • Agricultural intensification
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Diffuse pollution to surface waters due to agricultural and forestry activities
    • Nutrient enrichment (N, P, organic matter)
    • Air pollution, air-borne pollutants
    • Nitrogen-input
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Landfill, land reclamation and drying out, general
    • Flooding modifications
    • Water abstractions from surface waters
  • Natural biotic and abiotic processes (without catastrophes)
    • Biocenotic evolution, succession
    • Species composition change (succession)
    • Eutrophication (natural)
  • Climate change
    • Changes in abiotic conditions
    • Temperature changes (e.g. rise of temperature & extremes)
    • Changes in biotic conditions
    • Habitat shifting and alteration

Habitat restoration potential

Some sites of this habitat may recover in a time span of some tens of years to natural state, but in most cases interventions related to decline of nutrient loads from catchment areas and diminishing internal loading (in extreme cases by removal of sediment) are required.

Trends in extent

Average current trend in quantity

Stable Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

Most important conservation measures is decline of diffuse and point loading from catchment areas of the habitat type, along changing practices in agriculture and forestry. Active water protection measures are sometimes needed. The hydrological regime, including flooding, should be natural. Most representative sites should be legally protected, including their shoreline and littoral communities (in these cases there is need to have sufficient buffering areas with low land use intensity around the water bodies).

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
    • Restoring/Improving the hydrological regime
    • Managing water abstraction
  • Measures related to spatial planning
    • 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 limnic systems
  • Measures related to urban areas, industry, energy and transport
    • Urban and industrial waste management


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

EU28 Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Austria Present <1 Decreasing Decreasing
Belgium Present marginal Unknown Decreasing
Czech Republic Uncertain Unknown Unknown Unknown
Denmark Present Unknown Unknown Unknown
Estonia Present 5 Decreasing Decreasing
Finland mainland Present 6230 Decreasing Stable
Aland Islands Present 6230 Decreasing Stable
France mainland Present Oct-15 Decreasing Decreasing
Germany Present <3 Decreasing Stable
Ireland Present 407 Decreasing Stable
Italy mainland Present 0.1-0.5 Decreasing Decreasing
Latvia Present Unknown Unknown Unknown
Netherlands Present 0.4 Decreasing Decreasing
Poland Present Unknown Unknown Unknown
Portugal mainland Present 0.1 Unknown Decreasing
Romania Uncertain Unknown Unknown Unknown
Slovakia Present Unknown Unknown Unknown
Spain mainland Present 2 Decreasing Decreasing
Sweden Present 912 Unknown Stable
United Kingdom Present 11 Stable Stable
Greece (mainland and other islands) Uncertain Unknown Unknown Unknown
Lithuania Present Unknown Unknown Unknown
EU28 + Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Albania Uncertain Unknown Unknown Unknown
Iceland Present Unknown Unknown Unknown
Former Yugoslavian Republic of Macedonia (FYROM) Uncertain Unknown Unknown Unknown
Montenegro Present Unknown Unknown Unknown
Norway Mainland Present 4400 Unknown Stable
Switzerland Present x Decreasing Stable

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 5394350 3662 ca. 8000
EU28+ 3826 ca. 12500 Data from Norway has been estimated
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)
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