Red List habitat classification > RL - Marine habitats > RLBAL - Baltic > BAL21 Infaunal communities on Baltic infralittoral shell gravel

Infaunal communities on Baltic infralittoral shell gravel

Quick facts

Red List habitat type code BAL21
Threat status
Europe Endangered
EU Endangered
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 shell gravel according to the HELCOM HUB classification. The shell gravel fragments are coarse and well-sorted. This habitat is most often encountered in high energy exposure areas and is only found in the southern parts of the Baltic. Whilst macroscopic infauna are present, there is typically no macrovegetation or epibenthic macrofauna.  Two associated biotopes have been identified: 'Baltic photic shell gravel characterised by mixed infaunal macrocommunity in coarse and well-sorted shells and shell fragments' (AA.E3X) and 'Baltic photic shell gravel characterized by mixed infaunal macrocommunity in fine sand-like shell fragments' (AA.E3Y). The benthic macroinfauna species vary as the interstitial spaces are smaller in the latter sand-like shell gravel substrate, enabling burrowing polychaetes and amphipods to build tunnels using the small grains. 

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.

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

Threat status

Synthesis of Red List assessment

The habitat has a restricted distribution in the Baltic, currently only reported within the German EEZ. It is believed to have declined in extent, although by less than 25% in the last 50 years, due to degradation of the environmental quality caused by pollution. Current information suggests that the maximum area may be around 2,000 km2, based on presence in 100 x 100 km grid squares mapped by HELCOM.
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 associated biotope AA.E3Y Baltic photic shell gravel characterised by mixed infaunal macrocommunity in fine sand-like shell fragments as Near Threatened (B1a(ii). The other associated biotope (AA.E3X) was not evaluated.
Expert opinion is that this habitat should be assessed as Endangered (B1aii, B3) for both the EU 28and EU 28+. This is because of the relatively restricted distribution of the shell gravel habitat combined with past and predicted future decline in abiotic environmental quality. It is important to note some shortcomings with the EOO and AOO calculations. The data used to calculate EOO and AOO was based on HELCOM mapping in 100 x 100 km2 cells of only one of the two associated biotopes. The full extent and area covered by the habitat could therefore be greater. Equally relevant is that HELCOM information has been converted to 10 x 10 km cells to derive AOO. As the habitat may not occur in all the cells mapped this figure could be an over estimate. The confidence in this assessment is therefore given as Low.
Red List Category Red List Criteria
Endangered B1a(ii), B3
Red List Category Red List Criteria
Endangered B1a(ii), B3

Confidence in the assessment

Red List of habitat categories and criteria descriptions

Pressures and threats

  • Pollution
    • Pollution to surface waters (limnic, terrestrial, marine & brackish)
    • Nutrient enrichment (N, P, organic matter)
  • 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 extent and occurrence of the habitat needs to be mapped in more detail to establish whether it exists outside the German Exclusive Economic Zone. Measures to improve water quality are likely to benefit this habitat.

List of conservation and management needs

  • Measures related to wetland, freshwater and coastal habitats
    • Restoring/Improving water quality
  • Measures related to spatial planning
    • Other marine-related 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)
Belt Sea Present 2,000 Unknown Decreasing

Extent of Occurrence, Area of Occupancy and habitat area

Extent of Occurrence (EOO) (Km2) Area of Occupancy (AOO) Current estimated Total Area Comment
EU28 max 14,200 max 73 max 2,000 Based on presence in 100 x 100km grid squares therefore maximum potential EOO and AOO
EU28+ n/a n/a not present in EU28+ in the Baltic
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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1050 Copenhagen K
Phone: +45 3336 7100