AA.H1 Baltic photic muddy sediment characterized by macroscopic epibenthic biotic structures


HELCOM RED LIST Biotope Expert Team

Textual description

Baltic bottoms in the photic zone 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 µm). Coverage of macroscopic vegetation or sessile macroscopic epifauna is ≥10 %.

Physical environment

Salinity range: all; Exposure range: sheltered; Depth range: photic zone

Characteristic species

Phragmites australis, Stuckenia pectinata, Potamogeton perfoliatus, Najas marina, Chara tomentosa, Mytilus spp., Hediste diversicolor, Gammarus spp., Dreissena polymorpha, Valvata spp.

Mapping advise (habitat delineation, identification, similar types)

Photic zone areas with muddy sediment, such as soft clay, silt or mud. This includes mixed sediments where clay and/or mud are mixed with sand or gravel. Plants rooted or growing loose cover at least 10 % of the substrata. Rooted here includes roots and rhizoids of i.e. Charales.

Geographic range

Whole Baltic Sea

Anthropogenic threats


Correspondence with other classification systems

HELCOM 1998:
2.7 Muddy bottoms

2.7.2 Sublittoral photic zone by macrophyte vegetation

HELCOM 2007:

Macrophyte meadows and beds

  • habitat under threat and/or in decline in all areas of occurrence: Bothnian Bay, The Quark, The Bothnian Sea, Åland Sea, Archipelago Sea, Gulf of Finland, Gulf of Riga, The Southern Baltic Proper, The Gulf of Gdansk, Bay of Mecklenburg, Kiel Bay, Little Belt, Great Belt, The Sound, Kattegat

EUNIS 2012:

A5 Sublittoral sediment

A5.3 Sublittoral mud

A5.31 Sublittoral mud in low or reduced salinity

A5.311 Baltic brackish water sublittoral muddy biocenoses influenced by varying salinity


 Related information