Annual algae communities on Baltic infralittoral coarse sediment

This benthic habitat is distributed 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 according to the HELCOM HUB classification. Annual algae cover at least 10% of the bottom, while all other epibenthic biotic structures like perennial algae, rooted plants or blue mussels cover less than 10%. The habitat is present in the full salinity range of the Baltic Sea and is more common in exposed areas, mainly within the surf zone, in which wave energy prevents the establishment of either perennial vegetation or blue mussels.

One associated biotope has been identified: ‘Baltic photic coarse sediment dominated by Chorda filum and/or Halosiphon tomentosus’ (AA.I1S2). This is encountered in the Baltic Sea up to the Quark, and is identified by a large representation of Chorda filum and/or Halosiphon tomentosus, at least 50% of the biovolume of annual algae. 

Indicators of quality: 

The ratio of annual to perennial epibenthic components is used in several countries to describe habitat quality. As such the area of the habitat itself or the biomass of the corresponding species is used as an indicator for quality.In this particular case the lowest area or biomass is a sign of high quality as only in very high exposure levels should annual algae dominate. In all other circumstances perennials (Fucus) should dominate except where there is a low salinity (below 3 psu) as perennial algae growth does not generally occur under such conditions.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats