Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL34 Stable aggregations of unattached perennial vegetation on Baltic infralittoral muddy sediment

Stable aggregations of unattached perennial vegetation on Baltic infralittoral muddy sediment

Quick facts

Red List habitat type code BAL34
Threat status
Europe Least Concern
EU Least Concern
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)


This benthic Baltic Sea habitat occurs in the photic zone with at least 90% coverage of muddy sediment according to the HELCOM HUB classification. Stable aggregations of unattached perennial vegetation cover at least 10%, while perennial attached erect groups or Mytilus cover less than 10% of the bottom. The habitat is encountered in areas with salinity below 10 or 5 psu (depending on the area) and can be found in most of the Baltic Sea area, where the seabed is level over wide areas within the photic zone. The algae provide shelter and surface for attachment of invertebrates, however, if abundances of the unattached form are very high the sediment below may become deoxygenated and the associated infauna may die. The unattached forms of associated algae can coexist with attached forms and the characteristic rooted vegetation of bays, estuaries and lagoons.

Five associated biotopes have been described some of which have a more restricted distribution. These are variously dominated by unattached Fucus spp.,  Furcellaria lumbricalis, or by the dwarf form of Fucus species which coexists with attached F. vesiculosus, unattached Furcellaria lumbricalis, higher plants like Ruppia spp., Zannichellia palustris, Stuckenia pectinatus (formerly known as Potamogeton pectinatus), Zostera spp. and several charophytes. There are also biotopes dominated by stable aggregations of unattached rigid hornwort (Ceratophyllun demersum) and the unattached lake ball (Aegagropila linnaei).

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. For this habitat the density of unattached Fucus spp. (typical  and dwarf forms), lower limit of Furcellaria belt, amount of epiphytic algae, and density of Furcellaria are potential indicators of quality.

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

Threat status

Synthesis of Red List assessment

There have been significant declines in the biotope dominated by the typical form of Fucus which is characteristic of most of this habitat e.g. an estimated 20% decline over the past 50 years in some areas. The unattached Fucus dwarf form biotope is rare, and comparisons of historical records with the present distribution in German coastal lagoons give hints to a decline of >25% during the last 50 years. On the Swedish coast the decline is considerably larger.
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 the the unattached dwarf form of Fucus (AA.H1Q2) as Endangered (A1). The other biotopes (AA.H1Q1, AA.JHQ3, AA.H1Q4 and AA.H1Q5) were assessed as Least Concern (A1). The dwarf form is believed to constitute perhaps 1% of this habitat, consequently the overall assessment for this habitat type is Least Concern for both the EU 28 and EU 28+ because although there have been declines, taken together these are not believed to have exceeded 25% over the last 50 years.
Red List Category Red List Criteria
Least Concern -
Red List Category Red List Criteria
Least Concern -

Confidence in the assessment

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
    • 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
  • Climate change
    • Changes in abiotic conditions
    • Temperature changes (e.g. rise of temperature & extremes)
    • Wave exposure changes
    • Sea-level changes
    • Habitat shifting and alteration

Habitat restoration potential

The characteristic species Fucus vesiculosus and Furcellaria lumbricalis have a natural reproductive cycle of 1-2 years, but they take several years to reach full size. If the environmental conditions are favourable and there is a seed population available, the habitat can recover in the time from few years to a decade.

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

Combatting local sources of eutrophication (mainly agriculture) as well as restrictions on coastal construction and dredging in and around shallow coastal lagoons and archipelago areas can prevent decline in this habitat type.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to spatial planning
    • Establish protected areas/sites
    • Legal protection of habitats and species


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
Gulf of Riga
The Sound

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 >50000 Unknown Unknown This habitat is present in all the Baltic sub-basins.
EU28+ Unknown 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 Fucus vesiculosus
Algae Furcellaria lumbricalis
Flowering Plants Ceratophyllum demersum
Flowering Plants Potamogeton pectinatus
Flowering Plants Zannichellia palustris
Species scientific name English common name Species group
Fucus vesiculosus Algae
Furcellaria lumbricalis Algae
Ceratophyllum demersum Flowering Plants
Potamogeton pectinatus Flowering Plants
Zannichellia palustris Flowering Plants

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Phone: +45 3336 7100