Posidonia beds in the Mediterranean infralittoral zone
.jpg "European Red List of Habitats 2016")
.jpg "European Red List of Habitats 2016")
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).
Threat status
Synthesis of Red List assessment
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
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
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
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
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). |
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).
Characteristic species
Legal status
Relation to other habitat types mentioned in legal instruments
| Legal text | Annex | Name in legal text | Code in legal text |
Habitat type relationship |
More information |
|---|---|---|---|---|---|
| Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora - consolidated version 01/01/2007 | Annex I: natural habitat types of community interest whose conservation requires the designation of special areas of conservation | Posidonia beds (Posidonion oceanicae) | 1120 | Same | http://ec.europa.eu/environm...rective/index_en.htm |
