AB.M1E1 Baltic aphotic mixed substrate dominated by Mytilidae


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic aphotic zone bottoms with at least 10- 90 % coverage of hard (rock/boulders/stone) and 10-90 % soft substrata (e.g. muddy/coarse sediment/sand). Epibenthic bivalves cover at least 10 % of the seabed, and more than other perennial attached erect groups. Out of the epibenthic bivalves, Mytilidae constitutes at least 50 % of the biomass.


Substrate is soft or crystalline rock, boulders or stones mixed with mobile substrates such as sand or coarse substrate. Depth is typically from 20 to 100 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

Geographic range

Baltic Sea up to the Quark in the North



Correspondence with other classification systems               

HELCOM 1998:

2.8 Mixed sediment bottoms

2.8.1 Aphotic zone

EUNIS 2012:

A5 Sublittoral sediment

A5.4 : Sublittoral mixed sediments

A5.41 : Sublittoral mixed sediment in low or reduced salinity

A5.412 : Baltic mixed sediment bottoms of the 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