Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL4 Stable aggregations of unattached perennial vegetation on Baltic infralittoral mixed substrata (predominantly hard)

Stable aggregations of unattached perennial vegetation on Baltic infralittoral mixed substrata (predominantly hard)

Quick facts

Red List habitat type code BAL4
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 is a Baltic Sea benthic habitat in the photic zone where more tham 10% of the seabed is a mix of both hard and soft substrata according to the HELCOM classification. Stable aggregations of unattached perennial vegetation covers at least 10%, while perennial attached erect groups or Mytilus cover less than 10% of the bottom. The habitat occurs in most of the Baltic Sea area where the salinity is <10 or 5 psu (depending on the area), the exposure is sheltered and the seabed is level over wide areas within the photic zone.

Four associated biotopes with different dominant species of vegetation (constituting at least 50% of the biovolume) have been identified. ‘Baltic photic mixed substrate dominated by stable aggregations of unattached Fucus spp. (typical form)’ (AA.M1Q1) and ‘Baltic photic mixed substrate dominated by stable aggregations of unattached Furcellaria lumbricalis’ (AA.M1Q3) are encountered at depths of 0.5 to 5 meters. The unattached Furcellaria lumbricalis may occur in specific, ball-shaped morphology adapted to soft bottom conditions, and was historically described as Furcellaria cf. aegagropila.; ‘Baltic photic mixed substrate dominated by stable aggregations of unattached rigid hornwort (Ceratophyllum demersum)’ (AA.M1Q4) is encountered at a depth of 0 to 2 meters.

‘Baltic photic mixed substrate dominated by stable aggregations of unattached Fucus spp. (dwarf form)’ (AA.M1Q2) forms a characteristic biotope of shallow bays and lagoons between 0.25 and 2.5 m. This specific morphology of the Fucus spp. lacks bladders and holdfasts and the single plants can be loosely anchored in the sediment. Under more exposed conditions plants form a ball-shaped form, able to roll over the sea bottom. The Fucus dwarf forms coexist 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. The unattached thalli can cover the sediment up to about 10 cm height and thus form a three-dimensional habitat comparable to the interstitial space in coarse sediments. Epifauna is seldom attached to the Fucus dwarf form, but gastropods, amphipods and insects look for shelter and food in between the loose lying thalli. If abundances of the unattached form are very high, the sediment below becomes deoxygenated and the associated infauna below the Fucus layer may die. Presently this biotope is only known to occur in Sweden and Germany. In Germany it exists only in very few coastal lagoons with low to moderate eutrophication pressures and salinities of around 7–10 psu.

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.

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

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

Threat status

Synthesis of Red List assessment

This habitat is known to occur in all the sub-basins of the Baltic Sea although favouring sheltered areas. Information is also available on the distribution of the characteristic species (Fucus and Furcellaria). Declines in extent have mostly been reported for the unattached Fucus spp. dwarf form biotope (also the rarest biotope associated with this habitat) but areas dominated by other species (e.g. Furcellaria) have also seen a decline. In other cases (Fucus vesiculosus beds) modelled distributions suggest a possible increase in cover of attached forms.
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.M1Q2) as EN(A1). The other associated biotopes (AA.M1Q1, AA.M1Q3 and AA.M1Q4) were assessed as LC (A1). With no additional information on changes in extent or quality of this habitat, a known occurrence in all the Baltic Sea sub-basins, and less than a 25% decline in quantity over the last 50 years, current expert opinion is that this habitat should be assessed as Least Concern for the EU 28 and EU 28+.
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
  • 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)
    • Changes in biotic conditions
    • Habitat shifting and alteration

Habitat restoration potential

The characteristic species Fucus vesiculosus and Furcellaria lumbricalis have a natural reproduction 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, over periods of a 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 from agriculture) as well as conservation measures, such as restrictions on coastal constructions and dredging, in shallow coastal lagoons and archipelago areas can prevent damage and loss of this habitat.

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 605,075 482 Unknown This habitat is present in all the Baltic sub-basins.
EU28+ 482 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)
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