Stable aggregations of unattached perennial vegetation on Baltic infralittoral muddy sediment

This benthic Baltic Sea habitat occurs in the photic zone with at least 90% coverage of muddy sediment according to the HELCOM HUB classification. Stable aggregations of unattached perennial vegetation cover at least 10%, while perennial attached erect groups or Mytilus cover less than 10% of the bottom. The habitat is encountered in areas with salinity below 10 or 5 psu (depending on the area) and can be found in most of the Baltic Sea area, where the seabed is level over wide areas within the photic zone. The algae provide shelter and surface for attachment of invertebrates, however, if abundances of the unattached form are very high the sediment below may become deoxygenated and the associated infauna may die. The unattached forms of associated algae can coexist with attached forms and the characteristic rooted vegetation of bays, estuaries and lagoons.

Five associated biotopes have been described some of which have a more restricted distribution. These are variously dominated by unattached Fucus spp.,  Furcellaria lumbricalis, or by the dwarf form of Fucus species which coexists with attached F. vesiculosus, unattached Furcellaria lumbricalis, higher plants like Ruppia spp., Zannichellia palustris, Stuckenia pectinatus (formerly known as Potamogeton pectinatus), Zostera spp. and several charophytes. There are also biotopes dominated by stable aggregations of unattached rigid hornwort (Ceratophyllun demersum) and the unattached lake ball (Aegagropila linnaei).

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. For this habitat the density of unattached Fucus spp. (typical  and dwarf forms), lower limit of Furcellaria belt, amount of epiphytic algae, and density of Furcellaria are potential indicators of quality.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats