AB.M1F1 Baltic aphotic mixed substrate dominated by sea squirts (Ascidiacea)


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic aphotic zone bottoms with at least 10- 90 % coverage of hard (rock/boulders/stone) and 10-90 % soft substrata (e.g. muddy/coarse sediment/sand). Epibenthic chordates cover at least 10 % of the seabed, and more than other perennial attached erect groups. Out of the epibenthic chordates, sea squirts constitute at least 50 % of the biomass.


Substrate is soft or crystalline rock, boulders or stones mixed with mobile substrates such as sand or coarse substrate.

Characteristic species        

Ascidiacea: Dendrodoa grossularia, Molgula spp

Quality descriptors

Diversity, abundance and biomass of fauna

Geographic range

Kattegat and Belt Sea

Correspondence with other classification systems        

HELCOM 1998:
2.8 Mixed sediment bottoms
2.8.1 Aphotic zone
EUNIS 2012:
A5 Sublittoral sediment
A5.4 : Sublittoral mixed sediments
A5.41 : Sublittoral mixed sediment in low or reduced salinity
A5.412 : Baltic mixed sediment 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.M1F1