Communities of Mediterranean mediolittoral mud estuarine
|Red List habitat type||code MEDA2.31|
|Source||European Red List habitat factsheet|
|European Red List of habitats reports|
|European Red List of habitats (Excel table)|
In Mediterranean estuaries tidal amplitude is very weak and tidal currents, which generate vertical mixing of the water, are negligible. This favors vertical stratification of salinity with a counter current of saline water beneath the less dense river water.(salt wedge estuaries). The small tidal range (20-40cms) also means that large expanses of mediolittoral soft sediments along estuaries are rare, especially when compared to more northern latitudes in Europe.
This habitat is present on estuarine shores of soft substrates, generally under substantial freshwater influence, and may form a delta at the mouth of the estuary. It occurs in the mediolittoral and the upper part of the infralittoral where the sediment is fine sand, muddy sands and mud according to the course of the river bed. The banks are relatively stable, but the beds change with the violent winter flooding. The surface salinity is low (0.03 to 2.5 psu for the Rhône) whereas that of the deep layer, in contact with the benthic fauna, is much higher (16 to 21 psu for the Rhône). A marine salty patch typically lies underneath the fresh water of the river. Tides are weak and only cause minor changes in the water chemistry. The winds have a more marked influence on the position of the salty patch. When parts of the estuary or estuary lagoons are cut off, either naturally or by human action, the salinity of the water may increase considerably.
In the absence of the tide effect, the transition is rapid between the (freshwater) limnic environment and the marine environment. Thus there is no gradient in the distribution of the fauna, which occurs patchily. This habitat is characterized by communities of polychaetes, bivalves and oligochaetes. The species present are typically have short cycles of development that permit rapid colonization. The habitat is used as a feeding area by birds and by some fishes (grey mullet and eels).
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 may face; 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 over time.
Indices developed to assess the ecological status of coastal waters, including estuaries, according to the Water Framework Directive, include physical indicators, water quality indicators and measures of benthic diversity, species richness and abundance. The latter group, which is particularly relevant to benthic habitats, includes a Benthic Quality Index, an Infaunal Trophic Index, a Marine Biotic index based on ecological groups, and the Benthic Opportunistic Polychaetes/Amphipods Index.
Species typical of environments with high organic loads such as Capitella capitata, Heteromastus filiformis and Polydora spp. may be potential indicators of degraded quality. Indicators used within the Water Framework Directive may also be applied for estuarine habitats as a whole.
Synthesis of Red List assessment
There is a lack of quantiative data however expert opinion is that this habitat has suffered a decline in quantity of around 50% in the last 50 years. The pressures leading to these changes are predicted to continue therefore a continuing decline is likely. This habitat has therefore been assessed as Endangered for both the EU 28 and EU 28+.
|Red List Category||Red List Criteria|
|Red List Category||Red List Criteria|
Confidence in the assessment
Pressures and threats
- Use of biocides, hormones and chemicals
- Transportation and service corridors
- Roads, paths and railroads
- Shipping lanes, ports, marine constructions
- Port areas
- Shipping lanes
- Marine constructions
- Urbanisation, residential and commercial development
- Urbanised areas, human habitation
- Industrial or commercial areas
- Pollution to surface waters (limnic, terrestrial, marine & brackish)
- Marine water pollution
- Soil pollution and solid waste (excluding discharges)
- Natural System modifications
- Human induced changes in hydraulic conditions
Habitat restoration potential
Trends in extent
Average current trend in quantity
Trends in quality
Average current trend in quality
Conservation and management needs
List of conservation and management needs
- Measures related to wetland, freshwater and coastal habitats
- Restoring/Improving water quality
- Restoring/Improving the hydrological regime
- Measures related to marine habitats
- Restoring marine habitats
- Measures related to spatial planning
- Other marine-related measures
- Establish protected areas/sites
- Measures related to urban areas, industry, energy and transport
- Urban and industrial waste management
- Specific management of traffic and energy transport systems
- Managing marine traffic
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)|
|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||1,271,537||54||Unknown||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+||54||Unknown||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.|
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).
|Species scientific name||English common name||Species group|
Relation to other habitat types mentioned in legal instruments
|Legal text||Annex||Name in legal text||Code in legal text||
|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||Estuaries||1130||Overlap||http://ec.europa.eu/environm...rective/index_en.htm|