Epifaunal communities of Baltic upper circalittoral muddy sediment

This is a Baltic Sea benthic habitat in the aphotic zone where at least 90% of the substrate is  muddy sediment according to the HELCOM HUB classification. Sessile/semi-sessile epibenthic species cover at least 10% of the seabed and it is typically found below approximately 20 m in low to moderate energy exposure conditions. Six different biotopes associated with this habitat have been described. These are characterised by epibenthic bivalves, crustaceans, polychaetes and cnidarians, as well as biotopes with a mixed or sparse epibenthic community. Some of these biotopes have a restricted distribution in the Baltic e.g. those characterised by epibenthic polychaetes, or which have a sparse epibenthic macrocommunity which are only reported from The Belt Sea and The Sound. Aphotic muddy sediments characterised by epibenthic cnidarians are present in all the Baltic Sea sub-basins. 

Water movement is relatively limited in deep muddy areas and this creates a favourable environment for small tube-building amphipods such as Haploops spp. which can  be visible as a dense mat of tubes on the surface of the sediment. These are important feeding grounds for many species of fish including cod. Where seapens such as Virgularia mirabilis and Pennatula phosphorea dominate the epibenthos, for example in parts of the Kattegat trench and the Djupa Rännan trench, they also provide food and shelter for many other species, including commercially imporant fish. 

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. The amount of sediment covering the hard surfaces and the diversity, abundance and biomass of associated fauna are potential quality indicators for this habitat.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats