Emergent vegetation communities on Baltic infralittoral muddy sediment

This is a Baltic Sea benthic habitat in the photic zone where at least 90% of the substrate is muddy sediment according to the HELCOM HUB classification. Emergent vegetation covers at least 10% of the seabed and exceeds that of any other perennial attached erect groups. The habitat requires a salinity of less than 6 psu for the associated communities to develop and is encountered in sheltered areas down to a depth of 2 meters.  Two associated biotopes with different dominant plant species have been identified. The common reed (Phragmites australis) forms the characteristic biotope in water depths of up to 2m and in moderately exposed conditions, whereas sedges such as Schoenoplectus spp., and Bolbaschoenus maritimus are generally present in more sheltered and shallower waters in areas of low to moderate salinity.

In the Baltic Sea, sedges form large biotopes in shallow areas typically in estuaries and inlets. It can be found in very sheltered lagoons and in some estuaries around the whole Baltic Sea, but occurs mainly in the north along the Swedish and Finnish coasts of the Bothninan Bay and Gulf of Finland.  The species diversity is usually high because of the large variety and abundance of associated fish and birds. The benthic fauna consists mainly of soft-sediment invertebrates, such as polychaetes, crustaceans, bivalves and insect larvae. These shallow sheltered areas are of high biological productivity in a brackish environment. They form important breeding, resting, and feeding sites for water birds. The muddy substrate biotope dominated by the common reed (Phragmites australis) often occurs in the immediate vicinity of the biotope dominated by sedges and the two biotopes can form a mosaic.  Nutrient levels play a part in affecting the balance between the two biotopes with reed dominated areas favoured by conditions of eutrophication.

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 overall quality and continued occurrence of this habitat is, however, largely dependent on the presence of the emergent plant species which create the biogenic structural complexity on which the characteristic associated communities depend. The density and the maintenance of a viable population of these species is a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. In the case of this habitat the situation is further complicated because the reed dominated biotope is favoured by the deterioration of the sedge dominated biotope under conditions of eutrophication.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats