Red List of European Habitats
Habitat code & name
AB.B1E Baltic aphotic hard clay characterized by epibenthic bivalves
Author and Date
HELCOM RED LIST Biotope Expert Team, November 2013.
Relationship to EUNIS
The biotope does not correspond directly to any EUNIS (2004) level 4 habitats due to
structural differences the classification systems and the lack of the substrate ‘hard clay’ in
the relevant depth zones in the EUNIS-classification system. The closest correspondence in
EUNIS is found in the level 2 habitat ‘A4: Circalittoral rock and other hard substrata’.
Habitat description
Baltic aphotic zone bottoms with at least 90% coverage of hard clay. Sessile/semi-sessile
epibenthic bivalves have a coverage of at least 10%. Typically found in high exposure
exposure areas.
Two sub-biotopes with different dominant species of macrofauna can be identified:
‘Baltic aphotic hard clay dominated by Mytilidae’ (AB.B1E1) and ‘Baltic aphotic hard
clay dominated by Astarte spp.’ (AB.B1E4). The latter sub-biotope is characterized by
species preferring cold and saline water. The near bottom water exhibits a salinity range
between 10 and 15 psu, a temperature between 3 and 8°C and relatively good oxygen
conditions (Jan Warzocha pers. comm.) The easternmost occurrence for clams Astarte
borealis and Astarte elliptica is in the Baltic Sea. In the biotope they predominate in terms
of biomass, often contributing about 70–90% of the total biomass(Jan Warzocha pers.
comm.).
For ecological purposes, hard clay can be considered to be a hard substrate (HELCOM
1998). Very few macrofauna species have the capacity to burrow into the substrate.
Hard clay substrates are mostly known to occur mostly in high energy environments.
Characteristic species
Mytilus spp., Astarte borealis, Astarte elliptica
Indicators of quality
Diversity, abundance and biomass of fauna.
Relationships with other schemes
Annex 1 relationships
The relationship between HUB biotopes and Annex 1 habitats has not yet been mapped
by HELCOM.
MAES relationships
Marine - Coastal
MSFD relationships
Closest correspondence to
Shallow sublittoral rock & biogenic reef
Shelf sublittoral rock & biogenic reef
EUSeaMap relationships
Closest correspondence to
Shallow photic rock or biogenic reef
Shelf photic rock or biogenic reef
IUCN ecosystem relationships
Closest correspondence to 9.2 Subtidal rock and rocky reefs
Other relationships
Level 5 of the HELCOM HUB classification (2013). This habitat has two sub-habitats on HUB
level 6;
‘Baltic aphotic hard clay dominated by Mytilidae’ (AB.B1E1)
‘Baltic aphotic hard clay dominated by Astarte spp.’ (AB.B1E4)
Photograph
Pleas see the end of the document for a photograph on the subhabitat ‘Baltic aphotic
hard clay dominated by Astarte spp.’ (AB.B1E4).
Countries list
To be inserted when data sheets completed.
Regional Sea
Baltic Sea
Baltic Proper
Belt Sea
Gulf of Bothnia
Gulf of Finland
Gulf of Riga
The Sound
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Map
This will be inserted by NatureBureau based on the Regional Sea information above.
References
HELCOM (1998) Red list of marine and coastal biotopes and biotope complexes of the
Baltic Sea, Belt Sea and Kattegat. Balt Sea Environ. Proc. No 75
HELCOM (2007) HELCOM lists of threatened and/or declining species and
biotopes/habitats in the Baltic Sea. Balt. Sea Environ. Proc. No 113
HELCOM (2013) Approaches and met hods for eutrophication target setting in the Baltic
Sea region. Balt. Sea Environ. Proc. No. 133
Jan Warzocha personal communication, National Marine Fisheries Research Institute
(Poland),
(9.4.2013)
Biotope AB.B1E4 Aphotic hard clay dominated by Astarte spp. (Photo
Jan Warzocha)