Frondose algal communities (other than kelp) on exposed Atlantic infralittoral rock

This rocky habitat type is found in the infralittoral zone, in locations exposed or extremely exposed to wave action, or strong tidal streams. Associated biotopes are characterised by foliose red seaweeds, turfs of articulated Corallinaceae  and Cystosiera spp. at or below the lower limit of the kelp. Most of the red seaweeds which make up the dense turf of foliose red seaweeds are common to the kelp zone above, while the faunal component of the habitat is made up of species that are found either in the kelp zone or the animal-dominated upper circalittoral. Many of the red seaweeds, which occur in this habitat have annual fronds, which tend to die back in the autumn and regenerate again in the spring. This produces a seasonal change in the density of the seaweed cover, which is greatest between April and September, then substantially reduced over winter months. As well as a varied red seaweed component, this habitat may also contain occasional kelp plants and patches of the brown foliose seaweed Dictyota dichotoma. 

Dense fields of Cystoseira cf. abies-marina, are an associated biotope but currently only recorded on the Macaronesian archipelagos such as Formigas Bank, Azores and Chinijo Islets, north of Lanzarote, Canary Islands. Encrusting coralline algae frequently cover the substrate under the Cystoseira plants whilst Ulva rigida is an occasional epiphyte on the fronds. Around the various nooks and crevices of the irregular bedrock, the more abundant species are encrusting rhodophytes (calcareous and non-calcareous) as well as cartilagineous rhodophytes. Other species present are Sphaerococcus coronopifolius, Hypoglossum hypoglossoides, Dictyopteris membranacea and Cladophora sp.

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.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats