AB.A1E1 Baltic aphotic rock and boulders dominated by Mytilidae


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic bottoms in the aphotic zone with at least 90 % coverage of rock, boulders or stones of more than 63 mm in diameter. Epibenthic bivalves cover at least 10%of the seabed and more than other perennial attached erect groups. Out of the epibenthic bivalves, Mytilidae constitute at least 50 % of the biomass.

Physical environment       

Substrate is rock and/or boulders. Depth is typically from below 20 meters. Appears in all wave exposure classes. Salinity >5 psu.

Characteristic species        

Mytilus spp. and Modiolus modiolus

Quality descriptors

Amount of sediment. Diversity, abundance and biomass of fauna


Baltic Sea up to the Quark in the North



Correspondence with other classification systems               

HELCOM 1998:
2.1 Rocky bottoms

2.1.1 Soft rock Aphotic zone

2.1.2 Solid rock Aphotic zone

2.2 Stony bottoms

2.2.1 Aphotic zone


OSPAR list of threathened biotopes:

Modiolus modiolus beds

Habitat occurs in the OSPAR Region II (including Kattegat) and is listed threatened and/or declining in this region