Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL36 Submerged rooted plant communities on Baltic infralittoral muddy sediment

Submerged rooted plant communities on Baltic infralittoral muddy sediment

Quick facts

Red List habitat type code BAL36
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)


This Baltic Sea benthic habitat occurs in the photic zone with at least 90% coverage of muddy sediment according to the HELCOM  HUB classification.  The habitat covers the full salinity range of the Baltic Sea and is distributed from lagoons in the Belt Sea up to the northern part of Bothnian Bay. Muddy bottoms covered by rooted plants are mainly distributed in sheltered to very sheltered exposure conditions. In this habitat submerged rooted plants, including plants with rhizoids (i.e. Charales) cover at least 10% of the seabed and more than any other perennial attached erect groups. The charactersitic species depends on the salinity and depth.

Eight associated biotopes have been described. AA.H1B5 ’Baltic photic muddy sediment dominated by spiny naiad (Najas marina)’ has a restricted distribution at 0-1 m depth in extremely sheltered areas at low salinity (<4 psu).  AA.H1B8 ’Baltic photic muddy sediment dominated by spikerush (Eleocharis spp.)’ is also found in shallow (0-2 m depth) and sheltered areas with low salinity (<5 psu). AA.H1B1 ’Baltic photic muddy sediment dominated by pondweed (Potamogeton perfoliatus and/or Stuckenia pectinata)’ is found between 0.2-4 m depth in sheltered sites with up to 6 psu. AA.H1B3 ‘Baltic photic muddy sediment dominated by watermilfoil (Myriophyllumspicatum and/or Myriophyllumsibiricum)’ has a similar distribution but a more narrow depth range (0.2-2 m). AA.H1B6 ’Baltic photic muddy sediment dominated by Ranunculus spp.’ is also found up to 6 psu but is restricted to extremely sheltered sites. AA.H1B4 ’Baltic photic muddy sediment dominated by Charales’ is found in a wider range of salinity (2-15psu), depth (0.2-7 m) and wave exposure (low to moderate).AA.H1B2 ’Baltic photic muddy sediment dominated by Zannichellia spp. and/or Ruppia spp. and/or Zostera noltei’ is found at 0-4 m depth throughout the salinity gradient of the Baltic Sea and in low to moderate exposure. AA.H1B7 ’Baltic photic muddy sediment dominated by common eelgrass (Zostera marina)’ differs most strongly from the other associated biotopes in distribution, occurring mainly at moderate to high exposure, in salinities of 5 psu or higher and sedldom on muddy sediments. It is typically found deeper than the other associated biotopes (1-6 m) and often marks the lower depth limit distribution of soft bottom vegetation. This biotope is absent from areas with low salinity in the inner part of the Gulf of Bothnia.

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 overtime. 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. The vertical depth limit of submerged rooted plants is used in several countries as a Water Framework Directive parameter for assessing ecological status. 

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

Threat status

Synthesis of Red List assessment

The presence of this habitat type in the Baltic is well known. The best studied biotopes are those dominated by seagrass, brackish water angiosperms and charophytes. There have been significant declines (>25%) in the extent of the seagrass and Charales dominated communities in the last 50 years. Zostera marina and several species of Charales are also on the HELCOM Red List of threatened species in the Baltic.
The overall assessment for this EUNIS level 4 habitat has been based on the HELCOM (2013) assessments for the associated HELCOM HUB biotopes. Draft assessments were derived using a weighted approach whereby the HELCOM assessment outcomes were assigned a score. This was averaged across the relevant biotopes. The outcomes were reviewed by Baltic experts to reach a final conclusion. HELCOM (2013) assessed AA.H1B1, AA.H1B2, AA.H1B3 and AA.H1B6 as Least Concern (A1) and AA.H1B4, AA.H1B5 and AA.I1B7 as Near Threatened (A1). The overall assessment for this habitat type based on expert opinion is Near Threatened (A1) for both the EU 28 and EU 28+.
Red List Category Red List Criteria
Near Threatened A1
Red List Category Red List Criteria
Near Threatened A1

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Marine and Freshwater Aquaculture
    • Fishing and harvesting aquatic resources
    • Professional active fishing
    • Benthic or demersal trawling
    • Benthic dredging
  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Nutrient enrichment (N, P, organic matter)
    • Input of contaminants (synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, acute events
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Removal of sediments (mud...)
    • Estuarine and coastal dredging
    • Dykes, embankments, artificial beaches, general
    • Sea defense or coast protection works, tidal barrages
  • Climate change
    • Changes in abiotic conditions
    • Temperature changes (e.g. rise of temperature & extremes)
    • Sea-level changes
    • Changes in biotic conditions
    • Habitat shifting and alteration

Habitat restoration potential

The biotope dominated by common eelgrass (Zostera marina)’ can be slow to recover after strong decline (taking more than 20 yrs). Intervention may speed up the recovery but transplantation experiments have had limited success to date. Regeneration from root systems is slow and recovery of entire beds, with characteristic structure and associated species will take a long time. In the northern Baltic low salinity means that any expansion takes place vegetatively. Zostera plants are believed to be from the same genotype, estimated to be between 800-1600 years old. Clonal growth and low genetic diversity may reduce the acclimation capacity and survival of the species in rapidly changing environmental conditions. For the other associated biotopes natural recovery can probably occur within 10 years.

Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
EU28 EU28+

Conservation and management needs

All actions to reduce eutrophication of the Baltic Sea are important for the conservation of this habitat. For the associated biotopes that mainly occur in bays with limited water exchange with the open ocean (those dominated by Charales’ and the spiny naiad) combating local sources of eutrophication is essential. Conservation measures are also important, such as area protection and restrictions on coastal construction and dredging in shallow regions and archipelago areas.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to marine habitats
    • Restoring marine habitats
  • Measures related to spatial planning
    • Establish protected areas/sites
  • Measures related to urban areas, industry, energy and transport
    • Other measures
    • Managing marine traffic


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)
Baltic Proper Present Unknown Unknown Decreasing
Belt Sea
Gulf of Bothnia
Gulf of Finland
The Sound
Gulf of Riga

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 >50,000 >50 Unknown This habitat is present in all the Baltic sub-basins
EU28+ >50 Unknown This habitat is present in all the Baltic sub-basins
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.
Algae Chara tomentosa
Flowering Plants Myriophyllum spicatum
Flowering Plants Najas marina
Flowering Plants Potamogeton perfoliatus
Flowering Plants Ranunculus peltatus subsp. baudotii
Flowering Plants Ruppia maritima
Flowering Plants Stuckenia pectinata
Flowering Plants Zostera marina
Species scientific name English common name Species group
Chara tomentosa Algae
Myriophyllum spicatum Flowering Plants
Najas marina Flowering Plants
Potamogeton perfoliatus Flowering Plants
Ranunculus peltatus subsp. baudotii Flowering Plants
Ruppia maritima Flowering Plants
Stuckenia pectinata Flowering Plants
Zostera marina Flowering Plants

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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