AA.I1S2 Baltic photic coarse sediment dominated by Chorda filum and/or Halosiphon tomentosus


HELCOM RED LIST Biotope Expert Team

Textual description            

Baltic bottoms in the photic zone with at least 90 % coverage of coarse sediment. Coarse sediment has less than 20 % of mud/silt/clay fraction (<63 µm), and the proportion of gravel and pebbles (grain size 2–63 mm) exceeds 30% of the combined gravel and sand fraction . Annual algae cover at least 10 %, while all other vegetation covers less than 10 %.Out of the annual algae, Chorda filum and/or Halosiphon tomentosus constitutes at least 50 % of the biovolume.

Physical environment       

Salinity range: < 4.5 psu; Exposure range: moderate; Depth range: down to about 4 meters

Characteristic species        

Chorda filum, Halosiphon tomentosus


The key species are seasonal

Geographical RAnge

Baltic Sea up to the Quark


Decreased light penetration depth and increased sedimentation caused by eutrophication

Correspondence with other classification systems               

HELCOM 1998:

2.4 Gravel bottoms

2.4.2 Sublittoral photic zone Level bottoms dominated by macrophyte vegetation

EUNIS 2012:

A5 Sublittoral sediment

A5.5 Sublittoral macrophyte-dominated sediment