AB.M1G1 Baltic aphotic mixed substrate dominated hydroids (Hydrozoa)


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 cnidarians cover at least 10 % of the seabed, and more than other perennial attached erect groups. Out of the epibenthic cnidarians, hydroids 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. Depth is typically from 20 to 100 meters.

Characteristic species        

Laomedea spp, Cordylophora caspia

Quality descriptors

Diversity, abundance and biomass of fauna

Geographic range

Known from Russian waters

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