Red List habitat classification > RLB - Coastal habitats > RLA2.5c Atlantic coastal salt marsh

Atlantic coastal salt marsh

Quick facts

Red List habitat type code RLA2.5c
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 comprises natural grasslands on saline, clayey substrates along the coasts of the Atlantic Ocean, including the North Sea, characterized by halophytes. The northern limit of the habitat lies in northern Iceland and northern Norway (see habitat A2.5a), the southern limit lies in central Portugal (estuary of river Mondego),from which point southwards the salt marshes have predominantly Mediterranean characteristics. The most important factor for this azonal habitat is flooding by sea water, creating a gradient from lower, daily flooded parts towards higher parts with a low flooding frequency and duration and a more fluctuating soil salinity. With the flooding, sediments are brought in, and differences in sedimentation patterns (sand is deposited in the more dynamic parts, clay in low dynamic areas) creates a geomorphology of deep drainage channels (creeks), bordered by higher, sandy levees, with lower, clayey depressions behind. The salt marshes form transitions to bare mud flats on the lower elevation, and dunes or dune slacks on the higher part. These salt marshes are found in sheltered parts along the coast, like in lagoons, in sea inlets behind dunes, on the inland side of barrier islands, in estuaries, and in the Wadden Sea also on so-called “green beaches” (transition areas flooded both from North Sea and Wadden Sea) and rarely on sheltered parts of broad beaches.

The typical zonation of the North-Western Atlantic contains very open annual Salicornia species and perennial Spartina fields in the pioneer marsh (alliances Thero-Salicornion, Spartinion maritimae), open communities of Puccinellia maritima, Limonium vulgare, Halimione portulacoides , Triglochin maritima , Spergularia maritima and Plantago maritima in the lower salt marsh (alliance Puccinellion maritimae) and more closed communities of Juncus gerardi, Festuca rubra, Agrostis stolonifera, Armeria maritima, Elytrigia pycnanthus, Juncus maritimus and Artemisia maritima in the higher salt marsh (alliance Armerion maritimae). The latter form transitions towards brackish Potentillion anserinae communities (sometimes considered as Loto tenuis-Trifolion fragiferi Westhoff et Den Held ex de Foucault 2009) or towards Plantago coronopus, Sagina maritima and Cochlearia danica ommunities (alliance Saginion maritimae) on rarely flooded sand dunes. In places with seepage of freshwater, Blysmus rufus, Phragmites australis or Bolboschoenus maritimus may dominate the vegetation (alliance Scirpion maritimae). Also Apium graveolens and Oenanthe lachenalii are characteristic for such brackish transitions. Alpha diversity is in general low and rare species are few, for example Halimione pedunculata, Salicornia disarticulata, Scirpus americanus, Hordeum maritimum, Puccinellia fasciculata  and Bupleurum tenuissimum. In the thermo-Atlantic regions of Southwestern France, Northern Spain and Portugal, several other species with an Atlantic-Mediterranean distribution are found. In the first place several perennials chenopods grow here, like Sarcocornia perennis, Arthrocnemum fruticosum and Suaeda vera. Other ‘southern elements’ include Inula crithmoides, Juncus acutus, Frankenia laevis, Hutchinsia procumbens, Triglochin bulbosa subsp. barrelieri, Parapholis incurva, and Spartina maritima on the lower parts of the salt marsh.

Along the Atlantic coast saline meadows are also found in sites that have been embanked, sometimes centuries or decades ago, but still are fed with saline or brackish water. Such salt marshes often lack the typical  geomorphology but contain almost the same species composition as freely flooded salt marshes.  They are described here as part of Atlantic salt marshes; in most cases they only represent a small part of the area of the habitat type.

Many of the salt marshes along the Atlantic coast have a long tradition of extensive grazing. Ungrazed salt marshes are rare, but large examples exist, for instance in the Netherlands. No management leads, because of progressing clay sedimentation and nutrient enrichment, towards relatively species poor salt-marshes, were the lower belts are dominated by Halimione portulacoides, and the higher parts by Elytrigia atherica  (pycnanthus). Close to dunes or dikes Phragmites australis may dominate, but unlike in the Baltics, salinity and larger tidal fluctuations prevent reed to dominate large areas and threaten the diversity of the salt marshes. Therefore, reed beds form part of the Atlantic salt marshes, end in almost all cases these reed beds contain several halophytes. In general it is expected that low extensive grazing causes the highest biodiversity in Atlantic salt marshes.

Salt marshes are important stop overs on the fly ways of migrating birds. Puccinellia maritima for example provides a consistent diet for goose species. The habitat also is an important breeding and resting site for many waders. Besides for birds, salt marshes are important for specialized invertebrates (insects), many of them living just on one or a few halophytic plant species. They are considered as very productive ecosystems and the creeks form nurseries for some fish species, like Dicentrarchus labrax.

Salt marshes are threatened by drainage, building of hard sea defense systems (dikes), modification of the topography, invasive species (Spartina anglica, Spartina alterniflora) and eutrophication of the sea water. Sea level rise, resulting from climatic change, may cause erosion, especially of the pioneer belts with Salicornia where vegetation cover is very low.

Indicators of good quality:

The following characteristics are considered as indicators of good quality:

  • Pattern of branching creeks, with levees and depressions
  • Regularly flooding with sea water (absence of dikes…)
  • Presence of rare species
  • Low level or absence of invasive and nitrophilous species
  • Complete set of zonation belts, with no overrepresentation of certain belts
  • Absence of erosion

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

Threat status

Synthesis of Red List assessment

Atlantic salt marshes have undergone a reduction in area of about 26% in the EU countries during the last 50 years, while large parts (>60%) of the remaining area are negatively affected, with relatively high severity (58%). Such figures for countries outside the EU (mainly Iceland and Norway) are unknown, but assumed to be slightly better, but the habitat is mostly restricted to the EU and therefore the conclusion is applied to both the EU28 and EU28+ region. The severe reduction in quality parameters results in the Red List category Vulnerable (VU), while for reduction in quantity the category Near Threatened is scored.
EU
Red List Category Red List Criteria
Vulnerable C/D1
Europe
Red List Category Red List Criteria
Vulnerable C/D1

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Agriculture
    • Agricultural intensification
    • Abandonment / Lack of  mowing
  • Urbanisation, residential and commercial development
    • Discontinuous urbanisation
  • Invasive, other problematic species and genes
    • Invasive non-native species
  • Natural System modifications
    • Human induced changes in hydraulic conditions

Habitat restoration potential

The habitat is able to recover relatively quickly from degradation in a natural way, as long as sediment is available and there is a natural flooding regime by the sea.

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

For maintaining the diversity of salt marshes - often represented in the occurrence of different zonation belts (with different flooding regimes) - extensive grazing by cattle or sheep is known to be the optimum management. However, unmanaged salt marshes in Europe are relatively rare, and for some specific sites no management may be a relevant choice. In general no management (like abandonment) leads to relatively species-poor climax stages on salt marshes, but exceptions may occur, in cases where salt marshes are very dynamic and natural dynamics (flooding, goose and hare grazing) guarantee the occurrence of young succession stages for a long time. In some countries the prevention of bird hunting may be an important management action.

List of conservation and management needs

  • Measures related to agriculture and open habitats
    • Maintaining grasslands and other open habitats
  • Measures related to wetland, freshwater and coastal habitats
    • Restoring coastal areas
  • Measures related to spatial planning
    • Establish protected areas/sites
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of hunting and taking

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

EU28 Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Belgium Present 3.7 Decreasing Stable
Denmark Present 377 Decreasing Decreasing
Germany Present 250 Decreasing Decreasing
Ireland Present 53 Unknown Decreasing
Netherlands Present 136 Decreasing Decreasing
Portugal mainland Present 63 Decreasing Decreasing
Portugal Azores Uncertain 63 Decreasing Decreasing
Spain mainland Present 46 Decreasing Decreasing
United Kingdom Present 305 Decreasing Unknown
Northern Island Present 305 Decreasing Unknown
France mainland Present 540 Decreasing Decreasing
Sweden Present Unknown Unknown Unknown
EU28 + Present or presence uncertain Current area of habitat (Km2) Recent trend in quantity (last 50 years) Recent trend in quality (last 50 years)
Faroe Islands Uncertain - -
Guernsey Uncertain - -
Iceland Present Unknown Unknown Unknown
Isle of Man Uncertain - -
Jersey Uncertain - -
Norway Mainland Present Unknown Unknown Unknown

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 2652 4065300 1773 calculated
EU28+ 5900400 1800 estimated
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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1050 Copenhagen K
Denmark
Phone: +45 3336 7100