COUNTRYSIDE COUNCIL FOR WALES
SITE OF SPECIAL SCIENTIFIC INTEREST CITATION
YNYS MÔN ARFORDIR GOGLEDDOL PENMON
Local Planning Authority: CYNGOR SIR YNYS MÔN
National Grid Reference: SH 575814 – SH 641811
OS Maps: 1:50,000 Sheet number: 115
1:10,000 Sheet number: SH58SE & SH68SW
Extending over 7 km along the eastern tip of Anglesey (from Trwyn Du to west of Bryn Offa), this site is selected for its geological, botanical, ornithological and marine biological features.
The geological interest of the site comprises Tandinas quarry (a large disused limestone quarry) and associated north facing cliffs overlooking Traeth Coch. This site is the type locality for the Carboniferous Limestone Tandinas Formation, defined here at Tandinas Quarry, and which is the thickest and most complete section through this Asbian unit. The succession shows the finest Asbian examples of minor cycles, with many rhythmic repetitions of lithologies, frequently with just two beds representing a cycle. Terrestrial fabrics in the limestones are common, indicating emergence of the area as land. This is a key site for environmental interpretation in what was a very shallow marine to emergent situation in late Dinantian times. These beds have a common shelly fauna which is important for regional correlation within the Carboniferous Limestone outcrops of North Wales.
terrestrial interest of the
wet heath, calcareous dry heath, neutral grassland, maritime grassland and
base-rich flushes and the notable species
associated with these.
Situated largely on
Carboniferous Limestone sea cliffs and clifftop, this site enjoys the
relatively dry sunny climate of southeast Anglesey, although its northerly
aspect brings cool conditions and a later growing season. Limestone rock outcrops on the cliffs and
sporadically elsewhere but is often covered by glacial till, reflected in a
patchwork of soils and vegetation. Fedw Fawr common supports wet heath on peaty
gley soils. It is characterised by
quaking grass Briza media, columbine Aquilegia vulgaris, carline
thistle Carlina vulgaris and burnet rose Rosa pimpinellifolia.
Neutral grasslands with
common knapweed Centaurea nigra, crested dog's-tail Cynosurus
cristatus and bird’s-foot
lesser butterfly-orchid Platanthera
bifolia and green
Where lime rich water
flows down to the coast and cliff there are stands of flushed mire vegetation
characterised by a flora of black bog rush, blunt
Other notable species
, shag and a
large colony of cormorant and
also include the most southerly breeding colony of black guillemot in
The shore is the best example of marine communities typical of limestone shores exposed to moderate degrees of wave exposure in the area between Bardsey Island and Great Orme’s Head. It is also of special interest for the presence of diverse rockpool and rock overhang communities, extensive rocky shore community zonation patterns and for the presence of two communities of restricted national distribution. The topography of the shore is extremely varied, with steep limestone cliffs, and gently sloping or horizontal platforms with vertical or undercut edges and numerous eroded crevices. In places the cliffs have eroded to form beaches of cobbles, pebbles or huge boulders. This variety of habitats gives rise to a wide range of marine plant and animal communities.
Rocky shore communities form visible ‘zones’ down a good proportion of the shore. Such patterns of zonation are the result of different species’ tolerance’s to desiccation, temperature extremes and sunlight and their abilities to compete with other species for space. Yellow and grey lichen communities dominate bedrock and boulder surfaces above mean high water, with barnacles, the black tar lichen Verrucaria maura and the seaweeds channel wrack Pelvetia canaliculata and spiral wrack Fucus spiralis dominating rock surfaces immediately below. A wide band of barnacles, particularly the acorn barnacle Semibalanus balanoides, common limpets Patella vulgata and common mussels Mytilus edulis occurs on steep mid-shore sections. These sections are interspersed with gently sloping limestone platforms which are less exposed to wave action, and here the seaweed serrated wrack Fucus serratus is abundant within the barnacle, limpet and mussel zone. In places, however, the limestone platforms are scoured by sand and tidal action, such that the only species to survive are ephemeral species of seaweed with occasional clusters of common mussels in crevices.
Lower on the shore bedrock, boulder and cobble surfaces are covered by a range of seaweeds, including serrated wrack, and the red seaweeds Mastocarpus stellatus and Ceramium sp. At the lowest reaches oarweed Laminaria digitata forms a narrow zone along most of the shore. In places, vertical limestone bedrock and boulder surfaces in both the oarweed and the serrated wrack zones are burrowed into by piddocks and wrinkled rock borers Hiatella arctica. These communities are uncommon in Wales, being found only on a few limestone shores on north-east Anglesey, the Great Orme and south Pembrokeshire.
Diverse communities of marine plants and animals inhabiting rockpools and the surfaces under rock overhangs occur on this shore. Of particular interest are shallow rockpools with coral weed Corallina officinalis and other red seaweeds, as well as deeper rockpools with brown seaweeds (fucoids) and kelp, and sediment-floored rockpools with fucoids and other seaweeds. These rockpools occur along the length of the site. Under rock overhangs on the lower shore many species benefit from the damp, shaded conditions, including sponges (Haliclona viscosa, Hymeniacidon perleve, purse sponge Grantia compressa, breadcrumb sponge Halichondria panicea and boring sponge Cliona celata), sea-squirts (Morchellium argus and Botrylloides leachi), worms (Polydora sp., Pomatoceros sp. and greenleaf worm Eulalia viridis), anemones (Sagartia elegans and plumose anemone Metridium senile), and species of bryozoan, hydroid, soft coral, mollusc, barnacle and algae.
Certain areas of the site below mean high water form part of Y Fenai a Bae Conwy/Menai Strait and Conwy Bay candidate Special Area of Conservation (cSAC), under the EC Habitats Directive (Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora 1992). The site contains areas of Shallow Inlets and Bays and Reefs , habitats listed on Annex I of the Directive which are important features of the cSAC.
Between 1953 and January 2001, part of the site was notified as Fedw Fawr SSSI under the National Parks and Access to the Countryside Act, 1949. Parts of that site were renotified as Fedw Fawr – Caeau Ty Cydwys SSSI and Tandinas Quarry SSSI in 1994 under the Wildlife and Countryside Act 1981 (as amended).
This site is within the Anglesey Area of Outstanding Natural Beauty (AONB).
Biodiversity Action Plan Habitats of lowland heathland, unimproved
neutral grassland , fen and maritime cliff and slope s are found on
Part of this site has been selected in the Nature Conservancy Council’s Geological Conservation Review, a national survey and evaluation of sites of geological and geomorphological interest. The site is described in the following GCR volume: COSSEY, P.J. et al. In prep. British Lower Carboniferous Stratigraphy. Geological Conservation Review Series, Joint Nature Conservation Committee, Peterborough.