AB.H4U1 Baltic aphotic muddy sediment dominated by meiofauna


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). No macrocommunity present. Meiofauna constitutes at least 50% of the present biomass.

Physical environment       

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

Characteristic species        

Oligochaeta, Ostracoda, Nematoda

Quality descriptors

Diversity, abundance and biomass of meiofauna

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


 Related Information

This biotope has been listed as Near Threatened (NT) in the HELCOM Red List of Baltic Sea biotopes and habitats.

See the Biotope Information Sheet of AB.H4U1