AB.I1 Baltic aphotic coarse sediment characterized by macroscopic epibenthic biotic structures


HELCOM RED LIST Biotope Expert Team

Textual description            

Baltic aphotic bottoms 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. Coverage of sessile macroscopic epifauna is ≥10%.

Physical environment       

Salinity range: all; Exposure range: moderate to high; Depth range: aphotic zone

Characteristic species        

Mytilus spp, Hydrozoa, Amphibalanus improvisus

Mapping advise (habitat delineation, identification, similar types)             

Aphotic zone areas with coarse sediment such as gravel. Sediment must contain less than 20 % of mud/silt/clay fraction (<63 µm), and at least 30 % of grain size 2–63 mm. Coverage of sessile macroscopic epifauna is ≥10%.

Quality descriptors             

Diversity, abundance and biomass of fauna.

Geographic range               

Whole Baltic Sea

Anthropogenic threats     

Soft sediment covering the coarse sediment will decrease the quality.

Correspondence with other classification systems               

HELCOM 1998:
2.4 Gravel bottoms

2.4.1 Aphotic zone

EUNIS 2012:

A5 Sublittoral sediment

A5.1 Sublittoral coarse sediment

A5.11 Infralittoral coarse sediment in low or reduced salinity

A5.114 : Baltic gravel bottoms of the aphotic zone