AA.M1E2 Baltic photic mixed substrate dominated by Zebra mussel (Dreissena polymorpha)


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic photic bottoms with 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, Zebra mussel constitutes at least 50 % of the biomass.

Physical environment       

Substrate is soft or crystalline rock, boulders or stones mixed with mobile substrates such as sand or coarse substrate. Depth is typically from 2 to 10 meters. Appears in sheltered to moderately exposed areas. Salinity must be less than 5 psu.

Characteristic species        

Dreissena polymorpha

Quality descriptors

Amount of sediment. Diversity, abundance and biomass of fauna


Estonian west coast and eastern Gulf of Finland

Correspondence with other classification systems               

HELCOM 1998:

2.8 Mixed sediment bottoms

2.8.2 Sublittoral photic zone With little or no macrophyte vegetation

EUNIS 2012:

A5 Sublittoral sediment

A5.4 : Sublittoral mixed sediments

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

A5.411 : Baltic level mixed sediment bottoms of the infralittoral photic zone with little or no macrophyte vegetation