Seagrass beds on Atlantic infralittoral sand (non-Macaronesian)

This habitat type covers beds of submerged marine angiosperms in the genera Zostera, Ruppia, and Cymodocea, adjacent to mainland coasts of the North East Atlantic region. The Iberian coast is a transitional zone where Zostera dominated seagrass beds reach their southern limit and Cymodocea dominated seagrass beds reach their northern and western limits. Ruppia beds are restricted to brackish environments, where Zostera may be interspersed. Seagrass beds play an important role in the trophic status of marine and estuarine waters, acting in sediment stabilization as well as an important conduit or sink for nutrients and consequently some examples of Zostera marina beds have markedly anoxic sediments associated with them.  It is a spawning area and it harbours increased densities of juvenile and medium sized fish species.

This habitat occurs in shallow sublittoral sediments, generally in sheltered embayments, marine inlets, estuaries and lagoons, with weak tidal currents and under conditoins of low, variable and full salinity. Whilst generally found on muds and muddy sands, particularly marine examples of Zostera communities may also occur in coarser sediments. Whilst the seagrass may be considered an epibiotic overlay of established sedimentary communities it is likely that its presence will modify the community offering living space and feeding ground for epibionts and phytal specialists. For example, Zostera beds in the south-west of Britain may contain conspicuous and distinctive assemblages of Lusitanian fauna such as Laomedea angulata, Hippocampus spp. and Stauromedusae. These subtidal beds of Zostera contain the specific perennial variant of Zostera marina. Cymodocea nodosa forms large and dense patches with green leaves that can reach 100 cm long and 8 mm wide in well shorted fine sands or on superficial muddy sands in sheltered waters and depths of 1-30 meters. Frequently it is mixed with other habitat forming phanerogams Zostera noltei (formerly known as Z.noltii or Z.nana) and Zostera marina on muddy sands rich in organic nutrients. Shallow meadows of Cymodocea and Zostera are usually found in sheltered bays close to harbours or in areas subject to human impact.

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.

The overall quality and continued occurrence of this habitat is, largely dependent on the presence of Zostera marina, which creates the biogenic structural complexity on which the characteristic associated communities depend. The density and the maintenance of a viable population of this species is a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. Seasonal and annual variations in shoot densities and canopy height can be used to evaluate habitat quality as well as acting as a proxy measure of habitat complexity and refuge capability. The vertical depth limit of submerged seagrass is used in several countries as a Water Framework Directive parameter for assessing ecological status. Other countries use area indices and/or density indices. Seagrass tissue nutrients have also been used as indicators of environmental change in these important ecosystems.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats