Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA2.31 Communities of Mediterranean mediolittoral mud estuarine

Communities of Mediterranean mediolittoral mud estuarine

Quick facts

Red List habitat type code MEDA2.31
Threat status
Europe Endangered
EU Endangered
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

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. 

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

Threat status

Synthesis of Red List assessment

This habitat has a wide range in the Mediterranean being present in all the sub-basins. It is considered likely to have declined significantly in extent in the recent past due to coastal development and urbanisation as well as the damming of rivers which has altered the hydrographic conditions and particularly the erosion and accretion of deltas where this habitat occurs.
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+.
EU
Red List Category Red List Criteria
Endangered A1; A2a,b.
Europe
Red List Category Red List Criteria
Endangered A1; A2a,b.

Confidence in the assessment

low
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Agriculture
    • Use of biocides, hormones and chemicals
    • Fertilisation
  • 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
    • Discharges
  • Pollution
    • 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

Unknown. Some of the associated species are able to recolonise rapidly, however where land claim has taken place, recovery will not be possible.

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

This habitat occurs in some protected areas. Beneficial conservation measures include regulating discharges to improve water quality, managing fisheries, establishing protected areas, coastal zone planning including zoning of developments, and whole estuary management including regulation of water abstraction from the river system and other activities which affect the hydrological regime. Direct engagement of stakeholders in the planning of the management process, and analysis of social and economic costs and benefits of different management options will be essential to the successful implementation of conservation actions.

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

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 Unknown 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 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.
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.
Invertebrates Abludomelita aculeata
Invertebrates Abra alba
Invertebrates Capitella capitata
Invertebrates Cerastoderma glaucum
Invertebrates Corophium volutator
Invertebrates Heteromastus filiformis
Invertebrates Hydroides dianthus
Invertebrates Iphinoe serrata
Invertebrates Malacoceros fuliginosus
Invertebrates Microdeutopus gryllotalpa
Invertebrates Mytilaster minimus
Invertebrates Naineris laevigata
Invertebrates Nephtys hombergii
Invertebrates Protoaricia oerstedii
Species scientific name English common name Species group
Abludomelita aculeata Invertebrates
Abra alba Invertebrates
Capitella capitata Invertebrates
Cerastoderma glaucum Invertebrates
Corophium volutator Invertebrates
Heteromastus filiformis Invertebrates
Hydroides dianthus Invertebrates
Iphinoe serrata Invertebrates
Malacoceros fuliginosus Invertebrates
Microdeutopus gryllotalpa Invertebrates
Mytilaster minimus Invertebrates
Naineris laevigata Invertebrates
Nephtys hombergii Invertebrates
Protoaricia oerstedii Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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