AB.H1E1 Baltic aphotic muddy sediment dominated by Mytilidae


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic bottoms in the aphotic zone with at least 90 % coverage of muddy sediment. The sediment must contain at least 20 % of mud, silt or clay (grain size less than 63 ┬Ám). 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.

Physical environment       

Substrate is muddy sediment. Appears in low to moderate energy exposure classes. Salinity >5 psu

Characteristic species        

Mytilus spp., Hediste diversicolor, Gammarus spp.

Quality descriptors

Diversity, abundance and biomass of fauna.

Correspondence with other classification systems               

HELCOM 1998:

2.7 Muddy bottoms

2.7.1 Aphotic zone

EUNIS 2012:

A5 Sublittoral sediment

A5.3 Sublittoral mud

A5.37 Deep circalittoral mud

A5.378 Baltic muddy bottoms of the aphotic zone