Annual algal communities on Baltic infralittoral rock and mixed substrata (predominantly hard)

This is a Baltic Sea benthic habitat in the photic zone where between 10-90% of the substrate is rock, boulders or stones or mixed  substrates according to the HELCOM HUB classification. Annual algae cover at least 10% of the seabed, while all other epibenthic biotic structures cover less than 10%. Annual algae can live as epiphytes (e.g. Pilayella/Ectocarpus on Fucus spp.or Aglaothamnion spp. on perennial red algae like Furcellaria or on Mytilus) where they may be considered quality descriptors, thus this habitat can be recognized only when annual algae grow directly on the hard substrate and not when they grow on perennial biotic structures. This habitat covers 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 perennial vegtation. Mapping should take place during the months when the vegetation is fully developed.

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