Description of biotope or habitat type
Fucus distichus and Fucus spiralis f. nana on extremely exposed upper shore rock
Habitat (physical) description
|Salinity||Full (30-35 ppt)|
|Wave exposure||Extremely exposed|
|Zone||Eulittoral - upper, Littoral fringe - lower|
Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.
- Records used to define the biotope (core records)
- Other records assigned to this biotope, marked as 'certain'
- Other records assigned to this biotope, marked as 'uncertain'
Point data based on records in the UK Marine Recorder Snapshot.
Extremely exposed gently or steeply sloping upper shore bedrock which supports a mixture of the wracks Fucus distichus and Fucus spiralis f. nana, the latter often at the top of the zone. On some sites F. distichus dominates and F. spiralis is not present. Other seaweeds normally found on exposed coasts are common in this biotope. These include ephemeral species such as the foliose red Porphyra umbilicalis and the green Enteromorpha spp. The winkles Melarhaphe neritoides and Littorina saxatilis can be found grazing on the bedrock or on the fucoids, while red crusts of Hildenbrandia rubra and the mussel Mytilus edulis are restricted to moist cracks and crevices. A sparse covering of the black lichens Verrucaria maura and Verrucaria mucosa can be found in the upper part of this biotope competing for space with barnacle Semibalanus balanoides and the limpet Patella vulgata. This biotope is very rare and restricted to the far north and west coasts.
This mixed band of F. distichus and F. spiralis f. nana is generally found between the Verrucaria maura and Porphyra spp. zone (Ver.Ver or Ver.B) above, and the M. edulis and barnacle zone below (MytB). It may also occur above a red algal zone consisting of Mastocarpus stellatus as recorded on Barra.
Due to the occurrence of this biotope on very exposed coasts a certain amount of fluctuation between this biotope and the Ver.B biotope from year to year is to be expected. More information is required to validate this hypothesis. There can be seasonal fluctuations in the density of ephemeral green algae.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
|Semibalanus balanoides||7||Occasional||81-100 %|
|Patella vulgata||11||Frequent||81-100 %|
|Littorina saxatilis||5||Common||41-60 %|
|Melarhaphe neritoides||7||Common||41-60 %|
|Mytilus edulis||4||Occasional||61-80 %|
|Porphyra umbilicalis||6||Frequent||61-80 %|
|Hildenbrandia rubra||5||Common||41-60 %|
|Fucus distichus||5||Frequent||61-80 %|
|Fucus spiralis||7||Common||61-80 %|
|Enteromorpha intestinalis||19||Common||81-100 %|
|Verrucaria maura||7||Frequent||61-80 %|
|Verrucaria mucosa||2||Frequent||21-40 %|