Submerged rooted plant communities on Baltic infralittoral coarse sediment

This benthic habitat occurs  in the photic zone with at least 90% coverage of coarse sediment according to the HELCOM HUB classification. Coarse sediments covered by rooted plants  (which also includes plants with rhizoids,i.e. Charales) are mainly distributed in areas of moderate exposure to wave actioin. The habitat covers the full salinity range of the Baltic Sea and is distributed from the Belt Sea up to the northern part of Bothnian Bay. Depending on the salinity the dominant species (>50% of the biovolume), defining the associated biotope type, varies. They also occupy different depth zones. Five associated biotopes have been identified: ’Baltic photic coarse sediment dominated by pondweed (Potamogeton perfoliatus and/or Stuckenia pectinata)’ (AA.I1B1); ’Baltic photic coarse sediment dominated by Ranunculus spp.’ (AA.I1B6 );  ’Baltic photic coarse sediment dominated by Charales’ (AA.I1B4);  ’Baltic photic coarse sediment dominated by Zannichellia spp. and/or Ruppia spp. and/or Zostera noltei’ (AA.I1B2) and  ’Baltic photic coarse sediment dominated by common eelgrass (Zostera marina)’ (AA.I1B7).

The latter differs most strongly from the other biotopes in distribution, occurring mainly at moderate to high exposure and in salinities of 5 psu or higher. It is typically found in deeper waters than the other 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 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 vertical depth limit of submerged rooted plants is used in several countries as a Water Framework Directive parameter for assessing ecological status. The overall quality and continued occurrence of this habitat is, however, largely dependent on the presence of the rooted 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.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats