Moderately exposed to wave-sheltered artificial substrata (such as steel wrecks/concrete pilings/cable debris etc) subject to moderately strong to weak tidal streams in the infralittoral zone. This habitat type is characterised by a dense covering of filamentous and foliose algae on vertical as well as the upper faces of the substrata. Although there are no biotopes currently defined under this biotope, due to the low number of records, it is suspected that this has been highly 'under-recorded', and that additional records will be added in the near future, leading to the definition of biotopes.