AB.H3P1 Baltic aphotic muddy sediment dominated by midge larvae (Chironomidae)


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic aphotic zone bottoms 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). Biomass of infaunal insect larvae dominates and is highest in the group that includes infaunal bivalves/polychaetes/crustaceans/echinoderms/insect larvae. Out of the infaunal insect larvae, Midge larvae (Chironomidae) constitute at least 50% of the biomass.

Physical environment       

Substrate is muddy sediment. Appears in all wave exposure classes.

Characteristic species        


Quality descriptors

Diversity, abundance and biomass of fauna

Anthropogenic threats


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