AA.D Baltic photic maërl beds


HELCOM RED LIST Biotope Expert Team

Textual description

Baltic bottoms in the photic zone with at least 90 % coverage of maerl (unattached particles of coralline red algae).

Physical environment

Salinity range: High; Exposure range: All; Depth range: Photic zone

Characteristic species

Lithothamnion spp. and Phymatolithon spp.

Mapping advise (habitat delineation, identification, similar types)

Photic zone beds of unattached particles of coralline red algae particles  (maximum diameter ≈5cm) in gravel and sand. Areas where maerl occur are generally well ventilated with low levels of turbidity at depths of 17-22 m. Maerlbeds have a patchy distribution.

Geographic range

Kattegatt; Lilla Middelgrund and Fladen

Anthropogenic threats

Extraction mining, ocean acidification, offshore wind-farms, destructive fishing methods and eutrophication causing increased turbidity

Correspondence with other classification systems

HELCOM 2007:

Maerl beds

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

- Kattegat

EUNIS (2012):

A5 Sublittoral sediment

A5.5 Sublittoral macrophyte-dominated sediment

A5.51 Maerl beds


OSPAR list of threathened biotopes:

Maerl beds

- habitat occurs in the OSPAR region II (including Kattegat) but is not 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 AA.D