Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL35 Annual algal communities on Baltic infralittoral muddy sediment

Annual algal communities on Baltic infralittoral muddy sediment

Quick facts

Red List habitat type code BAL35
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 Baltic Sea benthic habitat is occurs in the photic zone with at least 90% coverage of muddy sediment according to the HELCOM HUB classification. Annual algae cover at least 10% of the seabed, while all other epibenthic biotic structures like rooted plants, unattached perennial algae or blue mussels cover less than 10%. The habitat covers the full salinity range of the Baltic Sea and is common in sheltered, very shallow areas.  One associated biotope has been identified: ‘Baltic photic muddy sediment dominated by Vaucheria spp.’ (AA.H1S3). This is encountered most of the Baltic Sea with the exception of the more saline western parts (the Belt Sea and The Sound) and is identified by a large representation of Vaucheria spp., which constitutes at least 50% of the biovolume of the annual algae. It forms dense mats in bays with soft sediment, requires a salinity below 7 psu and is found at up to 7 meters depth.

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 is a lack of data on the extent, quantity and quality of this habitat but expert opinion is that it is unlikely to have declined in extent over the last 50 years.
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. This habitat was evaluated by HELCOM in the 2013 Red List of Habitat Assessment as Least Concern (A1). With no further baseline information or data on changes in extent or quality, the current expert opinion is an assessment of 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

  • No threats or pressures
    • No threats or pressures

Habitat restoration potential

As the dominant species of this biotope 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

Unknown Unknown
EU28 EU28+

Trends in quality

Average current trend in quality

Unknown Unknown
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 Unknown Unknown
Gulf of Bothnia
Gulf of Finland
Gulf of Riga
Belt Sea

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

Not available

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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