Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL45 Epifaunal communities on Baltic upper circalittoral coarse sediment and shell gravel

Epifaunal communities on Baltic upper circalittoral coarse sediment and shell gravel

Quick facts

Red List habitat type code BAL45
Threat status
Europe Near Threatened
EU Near Threatened
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 aphotic zone where at least 90% of the substrate is coarse sediment or shell gravel according to the HELCOM HUB classification. Sessile/semi-sessile epibenthic bivalves/epibenthic chordates cover at least 10% of the seabed and more than other perennial attached erect groups. The habitat typically occurs below 20m and is mostly encountered in high energy exposure areas. In offshore areas shell gravel bottoms are mainly found permanently at the same location whereas closer inshore they are more likely to shift dynamically from one location to another.

Six associated biotopes have been described; ‘Baltic aphotic shell gravel dominated by epibenthic bivalves (AB.E1E) where there is one sub-habitat with a large representation (at least 50% of the biomass) of Mytilidae’ (AB.E1E1) and ‘Baltic photic shell gravel characterised by epibenthic chordates (AB.E1F) with a sub-habitat dominated by vase tunicate (Ciona intestinalis) (AB.E1F1)'. The latter, which is only, present in the Belt Sea, occurs in areas where the bottom consists largely of mollusc shells or small shell fragments, often in small patches along with other sediments. Due to the combination of the extended interstitial space and the presence of biotic hard substrates, it is inhabited by a unique combination of endobenthic and epibenthic species, such as the vase tunicate (Ciona intestinalis). In these habitats coverage of epibenthic chordates is at least 10% of the sea floor, of which vase tunicate (Ciona intestinalis), which is largely annual in the Baltic, often constitutes at least 50% of the biomass. The tunicates might be overgrown by Ectocarpus spp. or Desmarestia spp. during summer in the photic zone. 

There are also associated aphotic shell gravel and coarse sediment biotopes characterised by mixed epibenthic communities (AB.I1V & AB.E1V) by epibenthic bivalves (AB.I1E) and shell gravel characterisied by a sparse epibenthic macrocommunities (AB.E2T).


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. Diversity, abundance and biomass of the dominant. species and associated fauna 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

The overall extent of this habitat is unknown although some biotopes are considered to have been stable over the last 50 years (aphotic shell gravel dominated by Mytilidae) and others (aphotic shell gravel dominated by vase tunicate) to have reduced in quantity by more than 25%. There is insufficient information on the quality of this habitat at the present time or over the last 50 years to reach a view on potential trends in quality.
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 biotopes AB.E1E1 and AB.I1E1 as Least Concern (A1). Biotope AB.E1F1 was assessed as Vulnerable (B1aii) . Three biotopes (AB.E1V, AB.E2T and AB.I1V) were not evaluated. There is no quantitative data on the decline of the associated biotopes but given the past and predicted future pressures, most specifically where the substrate is comprised of shell gravel, expert opinion is that this habitat should be assessed as Near Threatened (A1) for both the EU 28 and EU 28+.
Red List Category Red List Criteria
Near Threatened A1
Red List Category Red List Criteria
Near Threatened A1

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Mining, extraction of materials and energy production
    • Exploration and extraction of oil or gas
  • 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
  • Natural System modifications
    • Human induced changes in hydraulic conditions
    • Removal of sediments (mud...)
    • Extraction of sea-floor and subsoil minerals (e.g. sand, gravel, rock, oil, gas)
    • Siltation rate changes, dumping, depositing of dredged deposits
    • Dumping, depositing of dredged deposits
  • Climate change
    • Changes in abiotic conditions
    • pH-changes

Habitat restoration potential


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

The distribution of this habitat should be mapped to gain better understanding of its environmental requirements. The area where the biotopes associated with shell gravel occur should be protected by prohibiting bottom trawling and other seabed disturbing activities. The oxygen conditions of the habitat need to be improved by reducing activities which lead to eutrophication.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to hunting, taking and fishing and species management
    • Regulation/Management of fishery in marine and brackish systems
  • Measures related to special resouce use
    • Regulating/Managing exploitation of natural resources on sea


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 Unknown Unknown This habitat is present in all the Baltic sub-basins however there is insufficient information for accurate calculation of EOO and AOO.
EU28+ Unknown Unknown This habitat is present in all the Baltic sub-basins however there is insufficient information for accurate calculation of EOO and AOO.
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.
Invertebrates Ciona intestinalis
Invertebrates Modiolus modiolus
Species scientific name English common name Species group
Ciona intestinalis Invertebrates
Modiolus modiolus Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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