Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL46 Infaunal communities in Baltic upper circalittoral coarse sediment and shell gravel dominated by bivalves

Infaunal communities in Baltic upper circalittoral coarse sediment and shell gravel dominated by bivalves

Quick facts

Red List habitat type code BAL46
Threat status
Europe Vulnerable
EU Vulnerable
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 upper circalittoral where at least 90% of the substrate is coarse sediment or shell gravel according to the HELCOM HUB classification. The substrate is usually poorly sorted with different proportions of gravel, coarse or medium sand, but may also contain finer sediment fractions. Macrovegetation and epibenthic macrofauna are generally absent and the biomass is typically dominated by infaunal bivalves. This habitat occurs in high energy exposure areas and two associated biotopes with different dominant species of macrofauna (at least 50% of the biomass) have been described.

‘Baltic aphotic coarse sediment dominated by multiple infaunal bivalve species: Macoma calcarea, Mya truncata, Astarte spp., Spisula spp.’ (AB.I3L10) is mainly restricted to small patches between hard substrates on ridges formed by lag sediment and till (e.g. Fehmarnbelt) in the photic and aphotic zone. It supports a high species diversity and high  biomass and only occurs in areas where the salinity exceeds 18 psu as all characteristic bivalve species are eumarine. For this reason it  has only been reported from the Kiel Bight to Isle of Fehmarn, and occasionally present from Mecklenburg Bight to the Darss Sill. 

‘Baltic aphotic coarse sediment dominated by multiple infaunal polychaete species including Ophelia spp.’ (AB.I3L11) is an associated biotope where biomass of bivalves still dominates but due to the large variety of interstitial space there is a specialised infauna, e.g., the polychaetes Ophelia limacina, O. rathkei and Travisia forbesii. This biotope is restricted to the Belt Sea (sandbanks) and parts of the ‘submerged belt’ of the Arkona Basin in the south-western Baltic Sea.  

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 havebeen 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

This habitat has a limited distribution in the Baltic, being confined to areas of high salinity where coarse sediments or shell gravel is also present. There is insufficient information on which to base a quantitative assessment of current area, and changes in quality and extent, however, expert opinion is that it has declined in area by approximately 25% during the past 50 years and that a continuing decline is likely. The quality of the habitat has in some areas shown moderate to severe reduction of 10-15% over the past 50 years and a further qualitative reduction of 10% is estimated over the next 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. HELCOM (2013) assessed the two biotopes AB.I3L10 and AB.I3L11 as Near Threatened (A1).
Current expert opinion is that this habitat should be assessed as Vulnerable under Criterion B for both the EU 28 and EU 28+ because of its restricted distribution and predicted continuing decline although, because it is present in very few 'locations' (defined by the extent of the main threats), it could also be considered Endangered. This assessment should be reviewed when more detailed mapping of the extent of this habitat has been undertaken because the EOO and AOO calculations used to apply Criterion B are based on data derived from a general mapping exercise.
Red List Category Red List Criteria
Vulnerable B1,2,3
Red List Category Red List Criteria
Vulnerable B1,2,3

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
    • 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
    • Siltation rate changes, dumping, depositing of dredged deposits
    • Dumping, depositing of dredged deposits

Habitat restoration potential


Trends in extent

Average current trend in quantity

Decreasing Decreasing
EU28 EU28+

Trends in quality

Average current trend in quality

Decreasing Decreasing
EU28 EU28+

Conservation and management needs

Bottom trawling and sediment extraction should be restricted in areas where this habitat occurs. All activities that can improve oxygen conditions through reduction of eutrophication will also support the conservation of the habitat. For the biotope ‘Baltic aphotic coarse sediment dominated by multiple infaunal polychaete species including Ophelia spp.’ (AB.I3L11) a Baltic-wide biotope inventory and a threat assessment is needed. For the time being this biotope should be considered as highly sensitive and worthy of protection.

List of conservation and management needs

  • Measures related to spatial planning
    • Establish protected areas/sites
  • 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 Decreasing Decreasing
Belt Sea
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 49,150 199 Unknown Based on presence in 100 x 100km grid squares therefore maximum potential EOO and AOO
EU28+ 199 Unknown This habitat is only present in the EU28
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 Macoma calcarea
Invertebrates Mya truncata
Invertebrates Ophelia limacina
Invertebrates Ophelia rathkei
Invertebrates Travisia forbesii
Species scientific name English common name Species group
Macoma calcarea Invertebrates
Mya truncata Invertebrates
Ophelia limacina Invertebrates
Ophelia rathkei Invertebrates
Travisia forbesii Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
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