AA.A1E1 Baltic photic rock and boulders dominated by Mytilidae


HELCOM RED LIST Biotope Expert Team

Textual description            

Baltic bottoms in the photic 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 5 to 20 meters. Appears in all wave exposure classes. Salinity must be at least 5 psu.

Characteristic species        

Mytilus spp. and Modiolus modiolus

Quality descriptors             

Amount of sediment and epiphytic annual algae. Diversity, abundance and biomass of fauna.

Geographic range               

Baltic Sea up to the Quark in the North.

Anthropogenic threats     


Correspondence with other classification systems               

HELCOM 1998: Sublittoral level soft rock bottoms with little or no macrophyte vegetation Sublittoral level stony bottoms with little or no macrophyte vegetation
EUNIS 2012:
A3.4 : Baltic exposed infralittoral rock
A3.5 : Baltic moderately exposed infralittoral rock
A3.6 : Baltic sheltered infralittoral rock

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