Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA5.535 Posidonia beds in the Mediterranean infralittoral zone

Posidonia beds in the Mediterranean infralittoral zone

Quick facts

Red List habitat type code MEDA5.535
Threat status
Europe Vulnerable
EU Vulnerable
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

This habitat is created by the ecosystem engineer species, the seagrass Posidonia oceanica. The plant of this seagrass consists of erected and plagiotropic rhizomes with at the top a 4 -8 leaves bundle, which has 8-11 mm wide and 20 to 80 cm long. The growth of the rhizomes allows the building of a specific structure called “matte” due to the accumulation of sediment between rhizomes and roots. This is a real engineering species, which constitutes characteristic formations called “Posidonia meadows” or “Posidonia beds”, between the sea- surface and 35 to 40 m depth. When the waters are particularly clear, these meadows can go deeper than 45 m deep (e.g. Corsica, Malta). They disappear when the salinity is below 33 % (optimum 35 to 39%). However, they support relatively large temperature variations from 9 to 29 ° C (17 optimum at 20 ° C). Posidonia beds can be present on various substrates (e.g. silt, fine sand, average and coarse, rocks), even if they prefer soft bottoms, rich in organic matter. This endemic species is the most widespread seagrass species throughout the Mediterranean. It is common on different types of substrate and habitats, from sandy bottoms to rocks. However, its biological characteristics with rare sexual reproduction and slow horizontal growth of rhizome edges, don’t allow a rapid recolonization of degraded or new forming beds.

Several sub-habitats have been described:

- Ecomorphosis of striped Posidonia oceanica meadows (A5.5351),

- Ecomorphosis of "barrier-reef" Posidonia oceanica meadows (A5.5352);

- Facies of dead "mattes" of Posidonia oceanica without much epiflora (A5.5353) and

- Association with Caulerpa prolifera on Posidonia beds (A5.5354).

 

Indicators of quality:

 

Posidonia oceanica is considered as good biological indicator of the quality of the marine environment and is considered as a biological quality element in the implementation of the European Framework Water Directive. Several descriptors are available to evaluate the quality of the Posidonia meadows habitat and many indicators of quality, based on combination of these descriptors have been established, particularly to monitor the habitat in the framework of European directives (e.g. Habitat, Fauna and Flora Directive, Water Framework Directive and recently Marine Strategy Framework Directive) or for conservation purposes (national or sub-national initiatives).  

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

Threat status

Synthesis of Red List assessment

Posidonia oceanica seagrass beds are an endemic habitat to the Mediterranean and represent the most widespread seagrass meadow in the region. A decline in surface area of 34% has been observed over the last 50 years due to mechanical damage from trawling, coastal development, pollution, boat anchoring, discharge of effluents and general decrease of water quality and sedimentation. The known decline trend at country level is on average 12% over the last 2-15 years but information is lacking regarding the trend in different Mediterranean countries.
There is limited information about a reduction in the habitat quality but the few reports at country level indicate a slight decline due to the mechanical alteration of the habitat (e.g. by fishing trawlers) and a decrease of the water quality (e.g. shoreline modification). Based on this information, this habitat has been assessed as Vulnerable under criteria A1 for both the EU 28 and EU 28+.
EU
Red List Category Red List Criteria
Vulnerable A1
Europe
Red List Category Red List Criteria
Vulnerable A1

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Benthic dredging
  • Pollution
    • Pollution to surface waters by industrial plants
    • Pollution to surface waters by storm overflows
    • Other point source pollution to surface water
    • Diffuse pollution to surface waters via storm overflows or urban run-off
    • Nutrient enrichment (N, P, organic matter)
    • Toxic chemical discharge from material dumped at sea
    • Input of litter (solid waste matter)
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Natural System modifications
    • Modification of hydrographic functioning, general
    • Dykes, embankments, artificial beaches, general
    • Altered water quality due anthropogenic changes in salinity
    • Other human induced changes in hydraulic conditions
  • Climate change
    • Temperature changes (e.g. rise of temperature & extremes)
    • Flooding and rising precipitations

Habitat restoration potential

The accumulation of different pressures and threats with the lack of genetic variability and slow growth, makes Posidonia oceanica habitat less resilient to disturbance and slow recovery. The species has a rare sexual reproduction and slow horizontal growth of rhizome edges that do not provide a rapid recolonization of degraded beds or the colonisation of new areas.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

Posidonia oceanica is protected by EU legislation (Habitat Directive), the Bern and Barcelona Conventions and some national legislations.
The habitat formed by this seagrass is also protected in various marine protected areas in the countries along the Mediterranean Sea. EU fishing regulations ban trawling activities near the shore (either above 50 m or 3 nm from the coast), giving indirect protection for this habitat (EC Council Regulation No. 1967, 21/12/2006). In some regions, more regulations are in place for fishing, shellfishing and aquaculture activities to be conducted on or above seagrass meadows to avoid negative impacts on the seagrasses. To prevent physical damage caused by trawling on the meadows, different measures should be put in place such as placing artificial reefs along certain stretches of the coast, developing effective surveillance programmes and enforcing the existing regulations to avoid illegal trawling. Awareness programmes with different sectors such as recreational boats and local councils will help to the better management of coastal activities and identifying areas where cost-effective schemes for threats reduction could be implemented. Mapping and monitoring efforts should target the remaining unmapped coastline (21,500 km) located in the southern and eastern regions of the basin and long term monitoring efforts should be in place to detect possible changes in the habitat.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to marine habitats
    • Other marine-related measures
    • Restoring marine habitats
  • 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 marine and brackish systems
    • Specific single species or species group management measures

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 12,247 Decreasing Decreasing
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 2,431,126 4,033 6,955 Source of current estimated total area:Telesca et al., 2015. EOO and AOO source: IUCN Red list (2015).
EU28+ 4,414 12,247 Source of current estimated total area:Telesca et al., 2015. EOO and AOO source: IUCN Red list (2015).
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 Caulerpa prolifera
Algae Flabellia petiolata
Algae Halimeda tuna
Algae Peyssonnelia squamaria
Algae Pneophyllum fragile
Fishes Chromis chromis
Fishes Coris julis
Fishes Diplodus vulgaris
Fishes Hippocampus hippocampus
Fishes Scorpaena porcus
Flowering Plants Posidonia oceanica
Invertebrates Achaeus cranchii
Invertebrates Alvania lineata
Invertebrates Bittium reticulatum
Invertebrates Calliostoma laugieri
Invertebrates Cerithium vulgatum
Invertebrates Cleantis prismatica
Invertebrates Columbella rustica
Invertebrates Electra posidoniae
Invertebrates Gammarella fucicola
Invertebrates Gibbula umbilicaris
Invertebrates Gourretia denticulata
Invertebrates Halocynthia papillosa
Invertebrates Hiatella arctica
Invertebrates Idotea balthica
Invertebrates Limaria hians
Invertebrates Lumbrineriopsis paradoxa
Invertebrates Marthasterias glacialis
Invertebrates Mediomastus capensis
Invertebrates Melita palmata
Invertebrates Microcosmus vulgaris
Invertebrates Miniacina miniacea
Invertebrates Modiolula phaseolina
Invertebrates Octopus vulgaris
Invertebrates Ophioderma longicauda
Invertebrates Ophiura ophiura
Invertebrates Pinna nobilis
Invertebrates Pisa nodipes
Invertebrates Pontogenia chrysocoma
Invertebrates Sepia officinalis
Invertebrates Sertularia perpusilla
Invertebrates Sirpus zariquieyi
Invertebrates Sphaerechinus granularis
Invertebrates Tricolia speciosa
Invertebrates Upogebia deltaura
Species scientific name English common name Species group
Caulerpa prolifera Algae
Flabellia petiolata Algae
Halimeda tuna Algae
Peyssonnelia squamaria Algae
Pneophyllum fragile Algae
Chromis chromis Damselfish Fishes
Coris julis African rainbow wrasse Fishes
Diplodus vulgaris Common two-banded seabream Fishes
Hippocampus hippocampus Sea horse Fishes
Scorpaena porcus Black scorpionfish Fishes
Posidonia oceanica Flowering Plants
Achaeus cranchii Invertebrates
Alvania lineata Invertebrates
Bittium reticulatum Invertebrates
Calliostoma laugieri Invertebrates
Cerithium vulgatum Invertebrates
Cleantis prismatica Invertebrates
Columbella rustica Invertebrates
Electra posidoniae Invertebrates
Gammarella fucicola Invertebrates
Gibbula umbilicaris Invertebrates
Gourretia denticulata Invertebrates
Halocynthia papillosa Invertebrates
Hiatella arctica Invertebrates
Idotea balthica Invertebrates
Limaria hians Invertebrates
Lumbrineriopsis paradoxa Invertebrates
Marthasterias glacialis Invertebrates
Mediomastus capensis Invertebrates
Melita palmata Invertebrates
Microcosmus vulgaris Invertebrates
Miniacina miniacea Invertebrates
Modiolula phaseolina Invertebrates
Octopus vulgaris Invertebrates
Ophioderma longicauda Invertebrates
Ophiura ophiura Invertebrates
Pinna nobilis Invertebrates
Pisa nodipes Invertebrates
Pontogenia chrysocoma Invertebrates
Sepia officinalis Invertebrates
Sertularia perpusilla Invertebrates
Sirpus zariquieyi Invertebrates
Sphaerechinus granularis Invertebrates
Tricolia speciosa Invertebrates
Upogebia deltaura Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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