When undertaking an appropriate assessment of impacts at a site, all features of European importance (both primary and non-primary) need to be considered.
Annex I habitats that are a primary reason for selection of this site
|The St Kilda archipelago is a westerly outlier of the Outer Hebrides and represents extremely wave-exposed reefs. The islands are formed of hard, igneous rock, which forms steep and vertical reefs around the entire island group. Littoral reef communities extend several metres above mean high water because of wave exposure, and populations of the uncommon exposed-shore fucoid Fucus distichus are present. Rock faces may extend sublittorally to reach depths of 50 m and support communities characteristic of very exposed conditions on rock walls, overhangs and ledges, in surge gullies and amongst boulders. The clarity of the Atlantic sea water is high, and dense kelp forests may occur as deep as 35 m. Sublittoral fringe biotopes which, elsewhere, are found only at low-water mark, may here reach depths of 12 m. Circalittoral rock is dominated by diverse communities of anemones, sponges and soft corals, with different species of sponge, hydroid and bryozoan occurring in surge gullies and caves.|
|1230 Vegetated sea cliffs of the Atlantic and Baltic Coasts|
|The St Kilda archipelago is a westerly outlier of the Outer Hebrides and represents hard acidic cliff habitat with extreme levels of maritime exposure. The sea cliffs of Hirta are the highest in the UK, reaching 426 m. Virtually the whole of each island is influenced by salt spray and the plant communities are dominated by maritime vegetation typical of Scotland. Roseroot Sedum rosea and Scots lovage Ligusticum scoticum are present on many of the vertical salt spray-drenched cliffs, with sea campion Silene uniflora and thrift Armeria maritima present in abundance. Diversity is increased by the presence of arctic-alpine plants, such as purple saxifrage Saxifraga oppositifolia and moss campion Silene acaulis. High humidity is reflected in widespread distribution of plants such as the liverwort Frullania teneriffae. St Kilda has some of the most extensive and best examples of this extreme form of Atlantic maritime vegetation in Europe.|
|8330 Submerged or partially submerged sea caves|
|The St Kilda archipelago is a westerly outlier of the Outer Hebrides and supports one of the most extensive sea cave systems in the UK. Throughout the island group basalt and dolerite dykes have eroded to form caves and tunnels above and below the water. The communities these support are diverse and reflect the degree of surge to which they are exposed. In shallow water in the extremes of surge the cave walls are blanketed only by the sponge Myxilla incrustans. With a reduction in surge, species such as the northern anemone Phellia gausapata are common, and thin encrusting sponges, bryozoans and the anemones Corynactis viridis and Sagartia elegans are abundant. Microhabitats in the deeper caves show a wave exposure gradient, with species usually found in more sheltered conditions, such as the fan-worm Sabella pavonina and the burrowing anemone Cerianthus lloydii, present in the inner regions. Rarely recorded nocturnal species have also been found in the inner caves, most notably the crab Bathynectes longipes and the anemone Arachnanthus sarsi.|
Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site
Annex II species that are a primary reason for selection of this site
Annex II species present as a qualifying feature, but not a primary reason for site selection
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.