Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL6 Annual algal communities on Baltic infralittoral rock and mixed substrata (predominantly hard)

Annual algal communities on Baltic infralittoral rock and mixed substrata (predominantly hard)

Quick facts

Red List habitat type code BAL6
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 between 10-90% of the substrate is rock, boulders or stones or mixed  substrates according to the HELCOM HUB classification. Annual algae cover at least 10% of the seabed, while all other epibenthic biotic structures cover less than 10%. Annual algae can live as epiphytes (e.g. Pilayella/Ectocarpus on Fucus spp.or Aglaothamnion spp. on perennial red algae like Furcellaria or on Mytilus) where they may be considered quality descriptors, thus this habitat can be recognized only when annual algae grow directly on the hard substrate and not when they grow on perennial biotic structures. This habitat covers the full salinity range of the Baltic Sea and is more common in exposed areas, mainly within the surf zone, in which wave  energy prevents the establishment of perennial vegtation. Mapping should take place during the months when the vegetation is fully developed.

Indicators of quality:

The ratio of annual to perennial epibenthic components is used in several countries to describe habitat quality. As such the area of the habitat itself or the biomass of the corresponding species is used as an indicator for quality.In this particular case the lowest area or biomass is a sign of high quality as only in very high exposure levels should annual algae dominate. In all other circumstances perennials (Fucus) should dominate except where there is a low salinity (below 3 psu) as perennial algae growth does not generally occur under such conditions. 

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

Threat status

Synthesis of Red List assessment

There are no quantitative data on the extent and area of this habitat but site records and distribution maps are available for some of the associated characteristic species. Expert opinion is that the extent is believed to have changed in extent by less than 10% over the past 50 years and that there have been only moderate changes in quality in some parts of the Baltic (<10%). No significant changes in extent or quality are envisaged for the near future.
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 three relevant Baltic sub-biotopes (AA.A1S, AA.M1S1 and AA.M1S2) to be of Least Concern (based on criterion A1). With no additional information on changes in extent or quality of this habitat, the current expert opinion is an assessment of 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

  • No threats or pressures
    • No threats or pressures

Habitat restoration potential

As the dominant species of this habitat are annual species, often known as opportunists with short life cycles, recovery can be very fast (1-2 years) even after strong declines.

Trends in extent

Average current trend in quantity

Stable Stable
EU28 EU28+

Trends in quality

Average current trend in quality

Stable Stable
EU28 EU28+

Conservation and management needs

No conservation and management measures specific to this habitat have been identified.

List of conservation and management needs

  • No measures
    • No measure known / impossible to carry out specific measures


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 Stable Stable
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 624,427 499 Unknown This habitat is present in all the Baltic sub-basins. occurs nearly everywhere, when light and substrate is adequate.
EU28+ >50 Unknown This habitat is present in all the Baltic sub-basins. occurs nearly everywhere, when light and substrate is adequate.
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

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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