Red List habitat classification > RL - Marine habitats > RLNEA - Atlantic > NEAA2.61 Seagrass beds on Atlantic littoral sediments

Seagrass beds on Atlantic littoral sediments

Quick facts

Red List habitat type code NEAA2.61
Threat status
Europe Near Threatened
EU Near Threatened
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

Mid and upper shore wave-sheltered muddy fine sand or sandy mud can have high densities of Zostera noltei (formerly known as Z.noltii or Z.nana) and/or Z.marinaZ.noltei forms stands with a cover of delicate trailing narrow leaves up to about 20 cm long. It survives the winter as rhizomes, therefore the locations remain stable over many years. It may occur monospecific, or with Z. marina or Ruppia sppand occasional plants of lower salt-marsh species such as annual Salicornia spp. or Spartina anglica, as stands of Z. noltei may not only pass downshore to Z. marina but also to communities of the lower saltmarsh, notably the Salicornietum europaeae. Exactly what determines the distribution of Z. noltei is not entirely clear. It is most characteristic of situations where the substrate dries out somewhat on exposure and, on flats with a gentle bar/hollow topography where it forms distinctive mosaics with Z. marina. It can also occur in shallow standing water and so is often found in small permanently submerged lagoons and pools, and on sediment shores where the muddiness of the sediment retains water and stops the roots from drying out. An anoxic layer is usually present some 5cm below the surface of the sediment. 

There may be seasonal variation in the area covered by intertidal seagrass beds, as plants die back in winter. Intertidal seagrass beds may also be subject to heavy grazing by geese, which can reduce the extent of the plant cover significantly. The rhizomes of Z.noltei will remain in place within the sediment in both situations and plants towards the lower limit may remain winter-green.

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. There are no commonly agreed indicators of quality for this habitat, although particular parameters may have been 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. Total area covered, density of the intertidal beds and species composition is, for example, used as a Water Framework Directive parameter for assessing ecological status. 

The overall quality and continued occurrence of this habitat is dependent on the presence of Zostera spp. which creates the biogenic structural complexity on which the characteristic associated species depend. The density and the maintenance of a viable population of Zostera is therefore a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. OSPAR defines Zostera beds as areas where plant densities should provide at least 5% coverage although, more typically they are greater than 30%. 

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

Threat status

Synthesis of Red List assessment

This habitat has a widespread distribution and is not limited to a few locations. Intertidal Z. marina beds may extend into the subtidal where they may develop into a perennial form with broad and long leaf and root systems (rhizomes) which survive in winter. The subtidal form disappeared in all but brackish regions around 1930 because of a disease and it is uncertain whether recovery is taking place. The intertidal form develops each year from seed and was not struck by the disease.
There are data on trends in quantity from many locations pointing to substantial historical declines in extent of this habitat over the last 150 years. Quality is also believed to have declined, due to both biotic and abiotic factors, however this is harder to quantify. The overall assessment is that habitat is Near Threatened on the basis of historical and recent declines in quantity and quality for both the EU 28 and EU 28+.
EU
Red List Category Red List Criteria
Near Threatened A1, A3, C/D3
Europe
Red List Category Red List Criteria
Near Threatened A1, A3, C/D3

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Fishing and harvesting aquatic resources
    • Professional active fishing
    • Leisure fishing
    • Bait digging / Collection
  • Human intrusions and disturbances
    • Other human intrusions and disturbances
    • Trampling, overuse
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Nutrient enrichment (N, P, organic matter)
    • Marine water pollution
    • Oil spills in the sea
    • Toxic chemical discharge from material dumped at sea
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Landfill, land reclamation and drying out, general
    • Modification of hydrographic functioning, general
    • Dykes, embankments, artificial beaches, general

Habitat restoration potential

Rapid recolonisation of damaged beds is possible if the disturbance causing the seagrass decline is limited in time and space and if seedlings originating from the sediment bank or from neighbouring populations experience suitable growth conditions the following year. If the seedlings die and recolonisation must rely on spreading from neighbouring populations, the process can be very slow. Partial recovery may take 10 years and full recovery may take 25 years.

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 protection of this habitat is often incorporated into legislation aimed at conservation of the seagrass beds e.g. local by-laws and regulations as well as cross border agreements covering large geographical areas as in the case of the Wadden Sea. It is also a characteristic feature of several habitat types listed in Annex 1 of the Habitats Directive.The establishment of protected areas and zoning as part of Integrated Coastal Zone Management plans has also been beneficial. These designations and plans can provide a framework under which specific measures such as restrictions on activities such as bait digging, clam raking and waste water management may be introduced. Transplantation experiments with seagrass have been attempted as a habitat restoration measure but with limited success to date.

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
    • 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

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)
Bay of Biscay and the Iberian Coast Present Unknown Decreasing Decreasing
Celtic Seas
Kattegat
Greater North Sea
Macaronesia

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 925,933 113 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+ >113 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.
Flowering Plants Ruppia maritima
Flowering Plants Spartina anglica
Flowering Plants Zostera marina
Invertebrates Arenicola marina
Invertebrates Cerastoderma edule
Invertebrates Hydrobia ulvae
Invertebrates Macoma balthica
Invertebrates Pygospio elegans
Invertebrates Scoloplos armiger
Species scientific name English common name Species group
Ruppia maritima Flowering Plants
Spartina anglica Flowering Plants
Zostera marina Flowering Plants
Arenicola marina Invertebrates
Cerastoderma edule Invertebrates
Hydrobia ulvae Invertebrates
Macoma balthica Invertebrates
Pygospio elegans Invertebrates
Scoloplos armiger Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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