AB.H1 Baltic aphotic muddy sediment characterized by macroscopic epibenthic biotic structures


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 µm). Coverage of sessile macroscopic epifauna is ≥10%.

Physical environment        

Salinity range: All; Exposure range: All; Depth range: Below photic zone ‑ more common in deeper areas.

Characteristic species        

Mytilus spp.

Mapping advise (habitat delineation, identification, similar types)             

Muddy sediment bottoms in the aphotic zone with at least 10 % coverage of epibenthic fauna.           

Geographic range               

Whole Baltic Sea

Anthropogenic threats     

Dredging, dredge spoil dumping, poisonous substances

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