Submerged rooted plant communities on Baltic infralittoral muddy sediment

This Baltic Sea benthic habitat occurs in the photic zone with at least 90% coverage of muddy sediment according to the HELCOM  HUB classification.  The habitat covers the full salinity range of the Baltic Sea and is distributed from lagoons in the Belt Sea up to the northern part of Bothnian Bay. Muddy bottoms covered by rooted plants are mainly distributed in sheltered to very sheltered exposure conditions. In this habitat submerged rooted plants, including plants with rhizoids (i.e. Charales) cover at least 10% of the seabed and more than any other perennial attached erect groups. The charactersitic species depends on the salinity and depth.

Eight associated biotopes have been described. AA.H1B5 ’Baltic photic muddy sediment dominated by spiny naiad (Najas marina)’ has a restricted distribution at 0-1 m depth in extremely sheltered areas at low salinity (<4 psu).  AA.H1B8 ’Baltic photic muddy sediment dominated by spikerush (Eleocharis spp.)’ is also found in shallow (0-2 m depth) and sheltered areas with low salinity (<5 psu). AA.H1B1 ’Baltic photic muddy sediment dominated by pondweed (Potamogeton perfoliatus and/or Stuckenia pectinata)’ is found between 0.2-4 m depth in sheltered sites with up to 6 psu. AA.H1B3 ‘Baltic photic muddy sediment dominated by watermilfoil (Myriophyllumspicatum and/or Myriophyllumsibiricum)’ has a similar distribution but a more narrow depth range (0.2-2 m). AA.H1B6 ’Baltic photic muddy sediment dominated by Ranunculus spp.’ is also found up to 6 psu but is restricted to extremely sheltered sites. AA.H1B4 ’Baltic photic muddy sediment dominated by Charales’ is found in a wider range of salinity (2-15psu), depth (0.2-7 m) and wave exposure (low to moderate).AA.H1B2 ’Baltic photic muddy sediment dominated by Zannichellia spp. and/or Ruppia spp. and/or Zostera noltei’ is found at 0-4 m depth throughout the salinity gradient of the Baltic Sea and in low to moderate exposure. AA.H1B7 ’Baltic photic muddy sediment dominated by common eelgrass (Zostera marina)’ differs most strongly from the other associated biotopes in distribution, occurring mainly at moderate to high exposure, in salinities of 5 psu or higher and sedldom on muddy sediments. It is typically found deeper than the other associated biotopes (1-6 m) and often marks the lower depth limit distribution of soft bottom vegetation. This biotope is absent from areas with low salinity in the inner part of the Gulf of Bothnia.

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 overtime. 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 vertical depth limit of submerged rooted plants is used in several countries as a Water Framework Directive parameter for assessing ecological status. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats