Red List habitat classification > RL - Marine habitats > RLMED - Mediterranean > MEDA5.32 Communities of Mediterranean sublittoral estuarine sediments

Communities of Mediterranean sublittoral estuarine sediments

Quick facts

Red List habitat type code MEDA5.32
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)


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). There are also distinct seasonal differences in salinity. In winter the estuary runoff from winter storms and greater flushing reduces the salinity. In spring, runoff becomes small and the estuary gradually returns to marine salinities. One consequence is that the benthos of the sublittoral sediments show rapid transitions from marine to freshwater species.

Typically there is an impoverished benthic macroinvertebrate community in the upper reaches of this estuarine habitat dominated by Tubificidae and Chiromidae. This contrasts with the lower reaches where there is a "salt wedge" community dominated by an abundance of polychates, molluscs and crustaceans. In shallower areas, beds of Cymodocea nodosa may be present. Species diversity is generally low but abundance may be high. Sudden influxes of salt water and drying up in the summer create recurrent disturbances that sometimes cause populations to disappear. In contrast, under oligotrophic conditions and long periods of salt wedge permance, the complexity of the benthic communites can increase. 

Indicators of quality:

Many indicators of quality have been used for this habitat with particular parameters set in certain situations e.g. protected features within Natura 2000 sites, where reference values have been determined and applied on a location-specific basis. 

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.

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 have altered the hydrographic conditions. The majority of Mediterranean estuaries are also considered likely to have declined in quality for similar reasons.
There is a lack of quantiative data however expert opinion is that it is reasonable to presume that this habitat has suffered declines in both quantity and quality in the last 50 years. The pressures leading to such declines are predicted to continue therefore a continuing decline is likely. This habitat has therefore been assessed as Vulnerable under criteria A1 and C/D1 for both the EU 28 and EU 28+.
Red List Category Red List Criteria
Vulnerable A1, C/D1
Red List Category Red List Criteria
Vulnerable A1, C/D1

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Agriculture
    • Use of biocides, hormones and chemicals
    • Fertilisation
  • Urbanisation, residential and commercial development
    • Urbanised areas, human habitation
    • Industrial or commercial areas
    • Discharges
  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Fishing and harvesting aquatic resources
  • 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 spatial planning
    • Other marine-related measures
    • Establish protected areas/sites
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish 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

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

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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