Seagrass beds on Atlantic littoral sand

This habitat has a widespread distribution and is not limited to a few locations. Intertidal Zostera marina beds may extend into the subtidal zone, where they may develop into a perennial form with broad and long leaf and root systems (rhizomes), which survive in winter.

Mid- and upper-shore wave-sheltered muddy fine sand or sandy mud can have high densities of Z. noltii (formerly known as Z. noltei or Z. nana), Z. marina and/or Ruppia spp. Z. noltii forms stands with a cover of delicate trailing narrow leaves that are up to about 20 cm long. As it survives the winter as rhizomes, the locations remain stable over several years. It may occur as monospecific, or with Z. marina or Ruppia spp. and with occasional plants of lower salt-marsh species, such as annual Salicornia spp. or Spartina anglica, as stands of Z. noltii may pass down shore not only to Z. marina, but also to lower saltmarsh communities, notably the Salicornietum europaeae. The factors that determine the distribution of Z. noltii are not entirely clear. This species is peculiar of situations where the substrate dries out on exposure, and on flats with a gentle bar/hollow topography, where it forms distinctive mosaics with Z. marina. It can also occur in shallow standing water; accordingly, it is often found in small permanently submerged lagoons and pools, and on sediment shores where the muddiness of the sediment retains water and stops the roots from drying out. An anoxic layer is usually present at about 5 cm below the surface of the sediment. Seasonal variation may occur in the area covered by intertidal seagrass beds, as plants die back in winter. Intertidal seagrass beds may also be subject to heavy grazing by geese, which can significantly reduce the extent of the plant cover. The rhizomes of Z. noltii will remain in place within the sediment in both situations, and plants towards the lower limit may remain winter-green.

This habitat has a widespread distribution and is not limited to a few locations. Intertidal Zostera marina beds may extend into the subtidal zone, where they may develop into a perennial form with broad and long leaf and root systems (rhizomes), which survive in winter.

Mid- and upper-shore wave-sheltered muddy fine sand or sandy mud can have high densities of Z. noltii (formerly known as Z. noltei or Z. nana), Z. marina and/or Ruppia spp. Z. noltii forms stands with a cover of delicate trailing narrow leaves that are up to about 20 cm long. As it survives the winter as rhizomes, the locations remain stable over several years. It may occur as monospecific, or with Z. marina or Ruppia spp. and with occasional plants of lower salt-marsh species, such as annual Salicornia spp. or Spartina anglica, as stands of Z. noltii may pass down shore not only to Z. marina, but also to lower saltmarsh communities, notably the Salicornietum europaeae. The factors that determine the distribution of Z. noltii are not entirely clear. This species is peculiar of situations where the substrate dries out on exposure, and on flats with a gentle bar/hollow topography, where it forms distinctive mosaics with Z. marina. It can also occur in shallow standing water; accordingly, it is often found in small permanently submerged lagoons and pools, and on sediment shores where the muddiness of the sediment retains water and stops the roots from drying out. An anoxic layer is usually present at about 5 cm below the surface of the sediment. Seasonal variation may occur in the area covered by intertidal seagrass beds, as plants die back in winter. Intertidal seagrass beds may also be subject to heavy grazing by geese, which can significantly reduce the extent of the plant cover. The rhizomes of Z. noltii will remain in place within the sediment in both situations, and plants towards the lower limit may remain winter-green.

In some areas, Z. marina may also be interspersed with Ruppia beds (Connor et al., 2004).

Expanses of clean or muddy fine sand and sandy mud in shallow water and on the lower shore (typically to about 5 m depth) can have dense stands of Z. marina/angustifolia. The community composition may be dominated by these Zostera species and, therefore, be characterised by the associated biota. Other biota present can be closely related to that of areas of sediment not supporting seagrass beds, for example Saccharina latissima, Chorda filum, and infaunal species, such as Ensis spp. and Echinocardium cordatum.

In southern areas, Cymodocea nodosa can also form patches in well sorted fine sands or on superficial muddy sands in sheltered intertidal zones. Frequently is mixed with other habitat forming phanerogams (Zostera noltii and Zostera marina) at muddy sands rich in organic nutrients. Shallow meadows of Cymodocea and Zostera are usually found in sheltered bays close to harbours, e.g. Cadiz Bay, or in areas subject to human impact.

In the North East Atlantic, C. nodosa is nowadays restricted to scattered locations from southern Portugal and Spain to Senegal, including Canary Island and Madeira. Southern Portugal constitutes the current northern geographic limit of its distribution.