Communities on Baltic infralittoral clay and other hard substrata

This is a Baltic Sea benthic habitat in the photic zone with at least 90% coverage of hard clay, marlstone rock, ferromanganese concretions and/or peat according to the HELCOM HUB classification. Sessile/semi-sessile epibenthic bivalves cover of at least 10% of the seabed and no perennial attached erect group has more than 10% coverage. In some cases macrovegetation or macrofauna may be absent. The habitat is typically encountered in high energy exposure areas. 

Seven associated biotopes have been identified. Four of these are associated with areas of hard clay and may be dominated (at least 50% of the biomass) by Mytilids (Mytilus spp., Modiolus modiolus), have a mixed epibenthic macrocommunity, a sparse epibenthic macrocommunity or have no dominant macrocommunity (AA.B1E1,  AA.B1V, AA.B2T and AA.B4U). The marlstone rock habitat  'AA.C: Baltic photic marl' is only present in the Baltic proper, Belt Sea and the Sound and  'AA.F: Baltic photic ferromanganese concretion bottoms' which is typically found below 10m occurs in Baltic proper, Gulf of Bothnia, Gulf of Finland, Gulf of Riga. 'AA.G: Baltic photic peat bottoms' which occurs in the Baltic proper and Belt Sea, has developed where marine erosion processes along the German and Danish coastline have laid these subfossil substrates bare. It is found salinity ranges between 7 and 18 psu, at all exposure classes and at depths from 0-20m. Knowledge about the latter biotope is scarce but the surface can be covered by filamentous annual algae and single juvenile Fucus spp. or Chorda spp. specimens. Normally peat bottom lacks epibenthic communities and only some specialised burrowing bivalves like Barnea candida or Zirfaea crispata may penetrate into the peat.

Indicators of quality;

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include: the presence of characteristic species as well as those which are sensitive to the pressures the habitat may face; water quality parameters; levels of exposure to particular pressure, and more integrated indices which describe habitat structure and function, such as trophic index, or successional stages of development in habitats that have a natural cycle of change over time.

There are no commonly agreed indicators of quality for this habitat, although particular parameters may have been set in certain situations e.g. protected features within Natura 2000 sites, where reference values have been determined and applied on a location-specific basis. Diversity, abundance and biomass of the dominate species and associated fauna are potential indicators of quality of this habitat.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats