Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL2 Perennial algal communities (excluding kelp) on Baltic infralittoral rock and mixed substrata (predominantly hard)

Perennial algal communities (excluding kelp) on Baltic infralittoral rock and mixed substrata (predominantly hard)

Quick facts

Red List habitat type code BAL2
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 at least 90% of the substrate is rock, boulders or stones and mixed (predominantly hard) substrates according to the HELCOM HUB classification. Perennial attached algae such as Fucus spp., or perennial red algae cover at least 10% of the seabed and more than other perennial attached erect groups. It is most common in areas exposed to wave action and typically occurs to depths of around 0.5 m.

Eight associated biotopes with different dominant species of algae have been described by HELCOM. ‘Baltic photic rock and boulders/mixed substrata dominated by Fucus spp.’ (AA.A1C1/AAM1C1) such as Fucus radicans, F. serratus or F. vesiculosus, is found in depths of 0.5–5m and in salinities over 4 psu. ‘Baltic photic rock and boulders/mixed substrata dominated by perennial non-filamentous corticated red algae’ (AA.A1C2/AA.M1C2) such as Furcellaria lumbricalis occurs at a depths of 2–10 m in similar salinities. These four biotopes are present in all the Baltic Sea sub-basins and are widely distributed, although not Bothnian Bay nor the most eastern part of the Gulf of Finland. ‘Baltic photic rock and boulders/mixed substrata dominated by perennial foliose red algae’ (AA.A1C3/AA.M1C3) such as Coccotylus spp., Phyllophora spp. and Delesseria spp. is typically found in depths of 2–10 m and in salinities over 4 psu. They are present in all the Baltic Sea sub-basins and are also widely distributed although also not in the Bothnian Bay nor the eastern half of the Gulf of Finland. ‘Baltic photic rock and boulders/mixed substrata dominated by perennial filamentous algae’ (AA.A1C5/AA.M1C5) such as Polysiphonia spp, Aegagrophila linnaei, Cladophora rupestris is found at depths of 0.5–10 m, in all the Baltic Sea sub-basins.

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

The lower depth limit of algae, especially Fucus spp. where applicable, and the amount of epiphytic algae 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

Changes in extent of this habitat have been reported in studies undertaken since the 1940s' and these reveal that Fucus and Furcellaria beds have declined and now occupy a narrower depth band in many places. In some areas it is estimated that up to 50% of the extent has been lost but on the whole Baltic Sea scale the reduction is believed to be less than 25%. In recent years some beds have also become re-established in places where they became absent in the 1990s'.
Reduction in habitat quality has also been apparent in some areas as changes in the algal and faunal species composition. This has been reported as an increase of abundance of smothering and fast growing filamentous annual macroalgae. There are concerns about possible future declines in extent and quality of this habitat. For example it has been suggested that if trends in temperature, total phosphorus concentration and chlorophyll a continue, water quality in the Bothnian Sea will deteriorate within 2-3 decades and reach levels that may lead to major losses of F. vesiculosis.
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 eight relevant Baltic biotopes to be of Least Concern (based on criterion A1). With no additional information on changes in extent or quality of this habitat, a restricted distribution, 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 both 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

  • Mining, extraction of materials and energy production
    • Mining and quarrying
    • Renewable abiotic energy use
  • 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
    • Siltation rate changes, dumping, depositing of dredged deposits
  • Climate change
    • Changes in abiotic conditions
    • Temperature changes (e.g. rise of temperature & extremes)
    • Habitat shifting and alteration

Habitat restoration potential

The characteristic species Fucus vesiculosus and Furcellaria lumbricalis have a short natural reproduction cycle of up to 5 years therefore if environmental conditions are favorable and there is a seed population available, the habitat can recover over timescales of a few years to a decade. Boulders are common in areas composed of lag deposits covering boulder clay of Pleistocene origin. Such areas have the potential for hard-bottom regeneration by natural abrasion where 'stone fishing' has removed the substrate. In other situations artificial reef creation may be an option.

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

Improvements in water quality (reduction of nutrient inputs) are considered to have been a major factor in the recovery of the perennial macroalgal habitat in the Baltic as this has increased light penetration and reduced the scope for rapid and blanketing smothering of the canopy-forming species by ephiphytic annual algae. Controls on coastal and offshore constructions to avoid increasing turbidity and direct removal or damage to the habitat are also important conservation and management measures.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to marine habitats
    • Other marine-related measures
  • Measures related to spatial planning
    • Establish protected areas/sites


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 >50,000 >50 Unknown Present in all the Baltic sub-basins
EU28+ >50 Unknown 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 Cladophora rupestris
Algae Coccotylus truncatus
Algae Delesseria sanguinea
Algae Furcellaria lumbricalis
Species scientific name English common name Species group
Cladophora rupestris Algae
Coccotylus truncatus Algae
Delesseria sanguinea Algae
Furcellaria lumbricalis Algae

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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