Seagrass beds on Atlantic infralittoral sand (Macaronesian)

This habitat consists of beds of submerged marine angiosperms in the genera Cymodocea, Halophila, Ruppia, Thalassia and Zostera in the southern islands of Macaronesia (it does not occur in the Azores). Seagrass beds are present mainly off the sheltered eastern coasts of the Canary Islands (Spain), on the wide subtidal platforms with sandy substrata and gently sloping coastlines which are sheltered from the Trade Winds. They may occur in patches or form extensive meadows reaching depths of over 30m where light levels are sufficient to support growth. C. nodosa has also been reported in scattered locations along the southern coast of Madeira Island (Portugal). In the Canary Islands, C.nodosa can be found forming unispecific meadows, but also mixed with Halophila decipiens on muddy bottoms or with the green macroalga Caulerpa prolifera on sandy bottoms.

Marine seagrass meadows are very important in providing several ecological services, such as primary production, habitats, nurseries and coastal protection. Primary productivity may vary, depending on many factors such as the density of the meadow, geographic area or hydrologic factors. These ecosystems are one of the most important habitats for several marine organisms, which depend on them in different phases of their life cycle, not only to feed but also to take shelter from predators.

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. Total area covered, density of the intertidal beds and species composition is, for example, used as a Water Framework Directive parameter for assessing ecological status.

The overall quality and continued occurrence of this habitat is dependent on the presence of seagrass species which create the biogenic structural complexity on which the characteristic associated species depend. The density and the maintenance of a viable population of seagrass is therefore a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. Shoot density and leaf length have both been examined as potential indicators of quality of this habitat.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats