AB.H2T1 Baltic aphotic muddy sediment dominated by sea pens


HELCOM RED LIST Biotope Expert Team

Textual description 

Baltic aphotic zone bottoms 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 ┬Ám). 0><10% of the seabed is covered by sessile macroscopic epifauna. Conspicuous populations of sea-pens are present in visual samplings.

Physical environment       

Substrate is muddy sediment. Depth is typically from 15 to 200 meters. Appears in low to moderate energy exposure classes.

Characteristic species        

Virgularia mirabilis, Pennatula phosphorea

Mapping advise (habitat delineation, identification, similar types)

Visual methods such as ROV:s of SCUBA diving are needed since it is possible that the animals will never appear in a grab-sample.

Quality descriptors

Diversity, abundance and biomass of fauna


Known from the Sound, Kattegat


Bottom trawling

Correspondence with other classification systems               

HELCOM 1998:

2.7 Muddy bottoms

2.7.1 Aphotic zone

HELCOM 2007:

Sea pens and burrowing megafauna communities

- habitat under threat and/or in decline in all areas of occurrence Kattegat

EUNIS 2012:

A5 Sublittoral sediment

A5.3 Sublittoral mud

A5.37 Deep circalittoral mud

A5.378 Baltic muddy bottoms of the aphotic zone


OSPAR list of threathened biotopes:

Sea-pen and burrowing megafauna communities

Habitat occurs in the OSPAR Region II (including Kattegat) and is listed threatened and/or in decline in this region

 Related Information

This biotope has been listed as Endangered (EN) in the HELCOM Red List of Baltic Sea biotopes and habitats.

See the Biotope Information Sheet of AB.H2T1