aa.H3P1–Baltic photic muddy sediment dominated by midge larvae (Chironomidae)


HELCOM RED LIST Biotope Expert Team

Textual description            

Baltic photic 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 µm). 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

2.7.2 Sublittoral photic zone With little or no macrophyte vegetation

EUNIS 2012:

A5 Sublittoral sediment

A5.3 Sublittoral mud

A5.31 Sublittoral mud in low or reduced salinity

A5.311 Baltic brackish water sublittoral muddy biocenoses influenced by varying salinity