Glannau Aberdaron

Site of Special Scientific Interest · 52.8046, -4.7460

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Gwynedd County LLYN Scenic Area

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Coastal

Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.

Habitats

Lowland dry heath, Lowland heath, Lowland wet heath

Geology & landscape

Geological Feature: Raised Beach, Rock Outcrop · Geological Period: Ordovician, Precambrian, Quaternary · Rock Type: Gneiss

Landscape processes: Coastal, Glacial

Birds & fish recorded

Birds

SpeciesSeason
fulmar Breeding
fulmar Roosting
peregrine Breeding
peregrine Roosting

Description

Description This site is of special scientific interest for features of geological, botanical, ornithological, and marine biological interest. The site extends along 10 km of coast dominated by sea cliffs, from Porth Oer on the north coast to Porth Simdde on the south coast of Pen Llŷn. Geological Interest The geological interest is at two locations: the outstanding exposures of Precambrian rocks overlain by Ordovician strata between Braich y Pwll and Parwyd and the Quaternary deposits at Porth Oer. Braich y Pwll – Parwyd (Precambrian of England and Wales). The coastal section between Braich y Pwll and Parwyd has long been recognized as one of the key locations in the Precambrian Mona Complex of North Wales. The site provides the finest exposures of the Gwna Mélange on Anglesey and Llŷn, and displays one of the clearest transitions from the Gwna Mélange into the Llŷn Shear Zone, the latter representing a major tectonic boundary that separates the recently defined Monian Composite and Cymru terranes. Although the contact between the Llŷn Shear Zone and Sarn Complex is cut out by a post-Arenig thrust, retrogressed garnetiferous gneisses, unique within the Mona Complex, are exposed on the east side of Parwyd. The Parwyd Gneiss represents the only outcrop of high-grade metamorphic basement in mainland North Wales. The unconformity with overlying Arenig strata is one of only three such occurrences on Llŷn, and constrains the deformation in the mélange to a pre-Arenig age. The section continues to be of crucial importance to the evolution of ideas on the origin of the Gwna Mélange. The Gwyddel Beds, for example, were originally thought to lie above the Gwna Mélange; detailed mapping, however, has shown that the Gwyddel Beds are in fact huge clasts within the chaotic Gwna Mélange which have retained original bedding and way-up characteristics. The superbly exposed transition from mélange to mylonitic rocks on Trwyn Bychestyn provides rare evidence indicating that the mélange is older than the Llŷn Shear Zone. This is a crucial factor in any reconstruction of Monian tectonic history. Porth Oer (Quaternary of Wales). Porth Oer provides important evidence for interpreting the Quaternary history of Llŷn. It demonstrates one of the finest examples of a raised shore platform in North Wales. This platform is cut across Precambrian rocks, and although its age is unknown, it is likely that it was fashioned, at least in part, during high relative sea levels in more than one Pleistocene interglacial. Sediments overlying the platform and in cliff sections at the site demonstrate the following generalized sequence: 1. parautocthonous deposits; 2. sands and gravels (locally cemented); and 3. interbedded diamictons and sands and gravels. The sands and gravels of unit 2 (Porth Oer Member) were formerly interpreted as interglacial raised beach deposits – one of only a few such postulated occurrences in North Wales. Accordingly, the site featured in numerous reconstructions of Pleistocene events in the region and was afforded reference status. However, recent work suggests that the sand and gravel deposits of unit 2 are more likely to be part of the extensively developed overlying glacigenic sequence at the site, which records a major incursion of the Irish Sea glacier onto Llŷn. Nonetheless, the site remains a critical reference site for its excellent example of a raised shore platform and overlying glacigenic sequence. Biological Interest Botanically, the cliffs and areas of western coastal heath with stands of bell heather Erica cinerea, western gorse Ulex gallii and ling Calluna vulgaris are plant communities of special interest. The heath found on Mynydd Anelog, Mynydd Mawr, Mynydd y Gwyddel, Mynydd Bychestyn and Pen y Cil is ‘wave formed’ in places, as a result of exposure to salt-laden winds. Between and within the heathland blocks, maritime grassland communities and localised flushes on boulder-clay slopes provide a contrasting flora and increase the diversity of the stands. The variety of rare and uncommon plants is also of special interest. The heath supports spotted rock rose Tuberaria guttata, only known elsewhere in Britain on Anglesey and prostrate broom Cytisus scoparius subsp. maritimus occurring here as a very isolated outlier at the north of its range. Golden samphire Inula crithmoides, lanceolate spleenwort Asplenium obovatum and an endemic sea-lavender Limonium procerum subsp. procerum also occur on the cliffs. Two nationally rare heathland lichens, the endangered Heterodermia leucomelos and the vulnerable Teloschistes flavicans, have been recorded from the site. Ornithologically the site supports an internationally important population of breeding chough Pyrrhocorax pyrrhocorax (20 pairs in 1997). Sea caves provide suitable nest sites, the cliffs provide roosting sites, and grazed rough grassland and heathland provide feeding areas. The site also supports a good diversity of cliff-nesting sea birds including species of gull, auks and fulmar, as well as peregrine. The marine biological interest includes bedrock cliffs which show the best example of wave-exposed rock habitat and its associated marine communities found between Bardsey Island and the great Orme. Complete community zonation characteristic of this habitat occurs along more than 8 km of the coast. The site is also of importance because of its species-rich rockpool and overhanging bedrock communities. This section of coast experiences strong wave action due to its westerly/south-westerly aspect. Steeply sloping narrow bedrock cliffs are present over most of the site, with caves and occasional storm beaches of boulders and cobbles. Between Porth Oer and Brach y Pwll the area of cliff subject to sea-spray supports a wide band of yellow and grey lichens. Below this the black tar lichen Verrucaria maura dominates, with the black lichen Lichina pygmaea also occurring regularly in this zone. Below the lichens a mixture of barnacles Semibalanus balanoides and limpets Patella sp. dominates the upper shore. From mid to low shore the community is characterised by foliose red and coralline seaweeds with thong-weed Himanthalia elongata. The zone below this is dominated by dabberlocks Alaria esculenta and oarweed Laminaria digitata, with an understorey of red seaweed. Caves in the cliff at Porth Llanllawen support a rich assemblage of sponges, ascidians, bryozoans and shade-tolerant seaweeds. The stretch of shore between Brach y Pwll and Porth Simdde forms the tip of Pen Llŷn and is subject to very strong tidal currents. The communities present are typical of a very exposed shore, with a very wide lichen zone consisting of black tar lichen below the orange lichens Caloplaca marina and Xanthorion parietinae. Further down the shore black tar lichen is associated with black lichen and laver Porphyra purpurea. The barnacles Chthamalus montagui and Semibalanus balanoides dominate the upper mid shore, and the periwinkle Littorina saxatilis inhabits their empty shells. In the most exposed areas the red seaweed Corallina officinalis dominates the lower shore, with Irish Moss Mastocarpus stellatus growing into a thick layer in slightly more sheltered areas. On the even more sheltered east-facing coast the red algae is overgrown by toothed wrack Fucus serratus. Species of Enteromorpha are the dominant seaweed in small sheltered bays along the coastline. Dabberlocks kelp covers the extreme low shore of the more exposed areas, while oarweed dominates this zone in less exposed areas. Remarks: 1. This site supports vegetation assignable to vegetated sea cliffs of the Atlantic and Baltic, and lowland heath. These are habitat types listed on Annex 1 of the EC Habitats Directive (Directive 92/43EEC on the Conservation of Natural Habitats and Wild Flora and Fauna). 2. Limonium procerum subsp. procerum and Heterodermia leucomelos are listed as priority Biodiversity Action Plan species. 3. The chough Pyrrhocorax pyrrhocorax is protected under Annex 1 of the EC Conservation of Wild Birds Directive 1979. 4. The lichens Heterodermia leucomelos and Teloschistes flavicans are protected under Schedule 8 of the Wildlife and Countryside Act 1981 (as amended). 5. The sea cliffs form part of the Clogwyni Pen Llŷn/Lleyn Sea Cliffs cSAC (Directive 92/43 EEC on the Conservation of Natural Habitats and Wild Flora and Fauna ). 6. The whole SSSI forms part of the Glannau Aberdaron and Ynys Enlli Special Protection Area (under the EC Conservation of Wild Birds Directive 1979). 7. The site is a component of the Lleyn Peninsula Environmentally Sensitive Area, the Lleyn Peninsula Heritage Coast and the Lleyn Peninsula Area of Outstanding Natural Beauty.

Species mentioned

English name
search for this in other sites		 Latin name
search with Google		 IUCN / Red List Type Family
dabberlocks Alaria esculenta Not listed in GB list algae brown alariaceae
serrated wrack Fucus serratus Not listed in GB list algae brown fucaceae
thong weed Himanthalia elongata Not listed in GB list algae brown himanthaliaceae
oar weed Laminaria digitata Not listed in GB list algae brown laminariaceae
common coral weed Corallina officinalis Not listed in GB list algae red corallinaceae
grape pip weed Mastocarpus stellatus Not listed in GB list algae red phyllophoraceae
acorn barnacle Semibalanus balanoides Not listed in GB list barnacle archaeobalanidae
chough Pyrrhocorax pyrrhocorax VU (Breeding) bird-corvid corvidae
fulmar Fulmarus glacialis CR (Breeding) bird-fulmar procellariidae
peregrine Falco peregrinus LC (Breeding) bird-hawk falconidae
Chthamalus montagui Not listed in GB list crustacean chthamalidae
lanceolate spleenwort Asplenium obovatum LC herb aspleniaceae
golden samphire Inula crithmoides Not listed in GB list herb asteraceae
rock sea-lavender Limonium procerum Not listed in GB list herb plumbaginaceae
spotted rock rose Tuberaria guttata VU herb cistaceae
Caloplaca marina Not listed in GB list lichen teloschistaceae
Lichina pygmaea LC lichen lichinaceae
powdered orange bush lichen Teloschistes flavicans VU lichen no common name
sea tar Verrucaria maura Not listed in GB list lichen no common name
no common name Xanthorion parietinae Not listed in GB list lichen no common name
Littorina saxatilis Not listed in GB list mollusc littorinidae
broom Cytisus scoparius LC shrub fabaceae
western gorse Ulex gallii LC shrub leguminosae
bell heather or ling Calluna vulgaris NT shrub dwarf ericaceae
bell heather Erica cinerea NT shrub dwarf ericaceae

Plant communities

H1 — Lowland dry heath

Calluna vulgaris-Festuca ovina heath

Calluna vulgaris, Erica cinerea, Erica tetralix, Ulex europaeus, Carex arenaria, Dicranella heteromalla, Dicranum scoparium, Hylocomium splendens, Hypnum cupressiforme, Pleurozium schreberi, Pseudoscleropodium purum, Polytrichum juniperinum, Ptilidium ciliare, Hypogymnia physodes, Cladonia arbuscula, Cladonia coniocraea, Cladonia fimbriata, Cladonia furcata, Cladonia impexa, Cladonia macilenta, Cladonia pyxidata, Cladonia squamosa, Cladonia tenuis, Cladonia uncialis, Cornicularia aculeata, Jacobaea vulgaris, Campanula rotundifolia, Cerastium fontanum, Teucrium scorodonia, Rumex acetosella, Galium saxatile, Agrostis capillaris, Deschampsia flexuosa, Festuca ovina, Holcus lanatus, Pteridium aquilinum

H2 — Lowland dry heath

Calluna vulgaris-Ulex minor heath

Pinus sylvestris, Sorbus aucuparia, Calluna vulgaris, Erica cinerea, Erica tetralix, Vaccinium myrtillus, Ulex europaeus, Ulex gallii, Ulex minor, Campylopus flexuosus, Dicranum scoparium, Hypnum jutlandicum, Polytrichum juniperinum, Polytrichum piliferum, Kurzia spp., Cladonia arbuscula, Cladonia chlorophaea, Cladonia coccifera, Cladonia fimbriata, Cladonia furcata, Cladonia impexa, Cuscuta epithymum, Genista anglica, Potentilla erecta, Rubus fruticosus agg., Agrostis canina, Agrostis curtisii, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Molinia caerulea, Pteridium aquilinum

H3 — Lowland dry heath, Lowland wet heath

Ulex minor-Agrostis curtisii heath

Quercus robur, Calluna vulgaris, Erica ciliaris, Erica cinerea, Erica tetralix, Ulex europaeus, Ulex minor, Carex pilulifera, Schoenus nigricans, Campylopus brevipilus, Campylopus flexuosus, Leucobryum glaucum, Hypnum jutlandicum, Polytrichum juniperinum, Kurzia spp., Hypogymnia physodes, Cladonia arbuscula, Cladonia coccifera, Cladonia crispata, Cladonia floerkeana, Cladonia impexa, Cladonia pyxidata, Cladonia uncialis, Cuscuta epithymum, Hypericum pulchrum, Polygala serpyllifolia, Potentilla erecta, Viola lactea, Agrostis curtisii, Danthonia decumbens, Molinia caerulea, Pteridium aquilinum, Zygogonium ericetorum

H4 — Lowland dry heath, Lowland wet heath, Upland dry heath

Ulex gallii-Agrostis curtisii heath

Salix repens, Calluna vulgaris, Erica ciliaris, Erica cinerea, Erica tetralix, Erica vagans, Vaccinium myrtillus, Ulex gallii, Carex binervis, Carex flacca, Carex montana, Carex panicea, Carex pilulifera, Trichophorum cespitosum, Juncus squarrosus, Luzula multiflora, Pohlia nutans, Campylopus flexuosus, Campylopus introflexus, Dicranum scoparium, Leucobryum glaucum, Racomitrium lanuginosum, Hypnum cupressiforme, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus squarrosus, Polytrichum juniperinum, Calypogeia fissa, Calypogeia muelleriana, Cephalozia bicuspidata, Diplophyllum albicans, Lophocolea bidentata, Hypogymnia physodes, Cladonia arbuscula, Cladonia chlorophaea, Cladonia coccifera, Cladonia crispata, Cladonia fimbriata, Cladonia floerkeana, Cladonia furcata, Cladonia impexa, Cladonia subcervicornis, Cladonia uncialis, Cuscuta epithymum, Lotus corniculatus, Thymus praecox, Pedicularis sylvatica, Polygala serpyllifolia, Polygala vulgaris, Potentilla erecta, Galium saxatile, Viola lactea, Agrostis canina, Agrostis capillaris, Agrostis curtisii, Anthoxanthum odoratum, Danthonia decumbens, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Molinia caerulea, Nardus stricta, Pteridium aquilinum

H5 — Lowland wet heath

Erica vagans-Schoenus nigricans heath

Salix repens, Calluna vulgaris, Erica cinerea, Erica tetralix, Erica vagans, Ulex europaeus, Ulex gallii, Carex flacca, Carex hostiana, Carex panicea, Carex pulicaris, Eriophorum angustifolium, Schoenus nigricans, Eleocharis multicaulis, Juncus acutiflorus, Juncus maritimus, Fissidens adianthoides, Kindbergia praelonga, Scorpidium scorpioides, Calypogeia fissa, Riccardia multifida, Angelica sylvestris, Eupatorium cannabinum, Serratula tinctoria, Succisa pratensis, Drosera rotundifolia, Genista anglica, Hypericum pulchrum, Scutellaria minor, Thymus praecox, Pinguicula lusitanica, Linum catharticum, Dactylorhiza incarnata, Dactylorhiza maculata, Gymnadenia conopsea, Platanthera bifolia, Pedicularis sylvatica, Plantago maritima, Polygala vulgaris, Anagallis tenella, Potentilla erecta, Sanguisorba officinalis, Galium uliginosum, Agrostis curtisii, Agrostis vinealis, Danthonia decumbens, Festuca ovina, Molinia caerulea, Phragmites australis, Chara curta

H6 — Lizard peninsula, Lowland heath

Erica vagans-Ulex europaeus heath

Calluna vulgaris, Erica cinerea, Erica tetralix, Erica vagans, Ulex europaeus, Ulex gallii, Prunus spinosa, Carex caryophyllea, Carex flacca, Carex panicea, Carex pulicaris, Schoenus nigricans, Campylopus flexuosus, Dicranum scoparium, Hypnum cupressiforme, Hypnum jutlandicum, Trichostomum brachydontium, Cladonia fimbriata, Cladonia furcata, Cladonia impexa, Daucus carota, Pimpinella saxifraga, Hypochaeris radicata, Leontodon saxatilis, Leucanthemum vulgare, Serratula tinctoria, Solidago virgaurea, Jasione montana, Anthyllis vulneraria, Lotus corniculatus, Centaurium erythraea, Geranium sanguineum, Hypericum humifusum, Hypericum pulchrum, Teucrium scorodonia, Thymus praecox, Scilla verna, Pedicularis sylvatica, Plantago lanceolata, Plantago maritima, Polygala serpyllifolia, Polygala vulgaris, Filipendula vulgaris, Potentilla erecta, Rubus fruticosus agg., Sanguisorba officinalis, Galium verum, Viola lactea, Viola riviniana, Agrostis capillaris, Agrostis curtisii, Agrostis vinealis, Aira caryophyllea, Anthoxanthum odoratum, Brachypodium sylvaticum, Dactylis glomerata, Danthonia decumbens, Festuca ovina, Festuca rubra, Holcus lanatus, Koeleria macrantha, Molinia caerulea, Pteridium aquilinum, Chara curta

H7 — Hard cliff and cliff slope, Lowland dry heath

Calluna vulgaris-Scilla verna heath

Salix repens, Empetrum nigrum subsp.nigrum, Calluna vulgaris, Erica cinerea, Erica tetralix, Erica vagans, Juniperus communis, Ulex europaeus, Carex caryophyllea, Carex flacca, Carex nigra, Carex panicea, Carex pulicaris, Carex serotina, Luzula campestris, Luzula multiflora, Selaginella selaginoides, Hypnum cupressiforme, Frullania tamarisci, Cladonia chlorophaea, Cladonia rangiformis, Daucus carota, Achillea millefolium, Hypochaeris radicata, Leontodon saxatilis, Leucanthemum vulgare, Scorzoneroides autumnalis, Serratula tinctoria, Jasione montana, Succisa pratensis, Cerastium diffusum, Cerastium fontanum, Silene uniflora, Sedum anglicum, Anthyllis vulneraria, Astragalus danicus, Genista pilosa, Lotus corniculatus, Trifolium repens, Centaurium erythraea, Thymus praecox, Scilla verna, Dactylorhiza purpurella, Euphrasia officinalis, Plantago coronopus, Plantago lanceolata, Plantago maritima, Armeria maritima, Polygala serpyllifolia, Polygala vulgaris, Rumex acetosa, Primula vulgaris, Filipendula vulgaris, Potentilla erecta, Galium verum, Viola riviniana, Agrostis capillaris, Agrostis stolonifera, Aira caryophyllea, Aira praecox, Anthoxanthum odoratum, Dactylis glomerata, Danthonia decumbens, Festuca ovina, Festuca rubra, Holcus lanatus, Koeleria macrantha, Molinia caerulea, Nardus stricta, Chara curta

H8 — Hard cliff and cliff slope, Lowland dry heath, Upland dry heath

Calluna vulgaris-Ulex gallii heath

Calluna vulgaris, Erica cinerea, Erica tetralix, Vaccinium myrtillus, Ulex europaeus, Ulex gallii, Carex binervis, Carex caryophyllea, Carex flacca, Carex pilulifera, Campylopus flexuosus, Dicranum scoparium, Hypnum cupressiforme, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus squarrosus, Polytrichum juniperinum, Polytrichum piliferum, Cladonia impexa, Cladonia squamosa, Hypochaeris radicata, Jasione montana, Lotus corniculatus, Hypericum pulchrum, Teucrium scorodonia, Thymus praecox, Scilla verna, Linum catharticum, Pedicularis sylvatica, Digitalis purpurea, Plantago lanceolata, Plantago maritima, Polygala serpyllifolia, Rumex acetosella, Potentilla erecta, Poterium sanguisorba, Rubus fruticosus agg., Galium saxatile, Galium verum, Viola lactea, Viola riviniana, Agrostis capillaris, Agrostis curtisii, Agrostis stolonifera, Agrostis vinealis, Aira praecox, Anthoxanthum odoratum, Avenula pubescens, Brachypodium sylvaticum, Dactylis glomerata, Danthonia decumbens, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Holcus lanatus, Molinia caerulea, Nardus stricta, Pteridium aquilinum, Chara curta

H11 — Lowland dry heath

Calluna vulgaris-Carex arenaria heath

Salix repens, Empetrum nigrum subsp.nigrum, Calluna vulgaris, Erica cinerea, Erica tetralix, Vaccinium myrtillus, Ulex gallii, Rosa spinosissima, Carex arenaria, Luzula campestris, Pohlia nutans, Campylopus introflexus, Ceratodon purpureus, Dicranum scoparium, Racomitrium canescens sens.lat., Hylocomium splendens, Hypnum jutlandicum, Pleurozium schreberi, Pseudoscleropodium purum, Rhytidiadelphus triquetrus, Polytrichum juniperinum, Polytrichum piliferum, Lophocolea bidentata, Ptilidium ciliare, Hypogymnia physodes, Cladonia arbuscula, Cladonia coccifera, Cladonia crispata, Cladonia floerkeana, Cladonia foliacea, Cladonia furcata, Cladonia gracilis, Cladonia impexa, Cladonia pyxidata, Cladonia rangiferina, Cladonia rangiformis, Cladonia subcervicornis, Cladonia uncialis, Cornicularia aculeata, Peltigera canina, Hypochaeris radicata, Jacobaea vulgaris, Pilosella officinarum, Teesdalia nudicaulis, Campanula rotundifolia, Jasione montana, Cerastium fontanum, Sedum anglicum, Lotus corniculatus, Ononis repens, Trifolium repens, Thymus praecox, Rumex acetosella, Potentilla erecta, Galium saxatile, Galium verum, Viola riviniana, Agrostis capillaris, Aira caryophyllea, Aira praecox, Ammophila arenaria, Anthoxanthum odoratum, Deschampsia flexuosa, Festuca ovina, Poa pratensis

M14 — Lowland dry heath, Upland wet heath

Schoenus nigricans-Narthecium ossifragum mire

Pinus sylvestris, Calluna vulgaris, Erica tetralix, Myrica gale, Ulex gallii, Carex panicea, Eriophorum angustifolium, Rhynchospora alba, Schoenus nigricans, Eleocharis multicaulis, Juncus acutiflorus, Juncus bulbosus, Ctenidium molluscum, Hypnum jutlandicum, Scorpidium revolvens, Scorpidium scorpioides, Sphagnum auriculatum, Sphagnum palustre, Sphagnum papillosum, Sphagnum subnitens, Sphagnum tenellum, Calypogeia fissa, Kurzia pauciflora, Ordontoschisma sphagni, Aneura pinguis, Riccardia multifida, Drosera intermedia, Drosera rotundifolia, Pinguicula lusitanica, Narthecium ossifragum, Pedicularis sylvatica, Polygala serpyllifolia, Anagallis tenella, Potentilla erecta, Molinia caerulea