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Special Areas of Conservation

Corsydd Môn/ Anglesey Fens

Designated Special Area of Conservation (SAC)
Country Wales
Unitary Authority West Wales and The Valleys
Centroid* SH470820
Latitude 53.3125
Longitude -4.295555556
SAC EU Code UK0012884
Status Designated Special Area of Conservation (SAC)
Area (ha) 465.04
* This is the approximate central point of the SAC. In the case of large, linear or composite sites, this may not represent the location where a feature occurs within the SAC.
Location of Corsydd Môn/ Anglesey Fens SAC

General site character

  • Inland water bodies (Standing water, Running water) (2%)
  • Bogs, Marshes, Water fringed vegetation, Fens (85%)
  • Heath, Scrub, Maquis and Garrigue, Phygrana (5%)
  • Dry grassland, Steppes (1%)
  • Humid grassland, Mesophile grassland (5%)
  • Mixed woodland (2%)

Download the Standard Data Form for this site (PDF <100kb)

Note 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

  • Within Anglesey Fens, Llyn Yr Wyth Eidion is a small active marl-producing lake in north Wales and is an example of a lake on limestone. It is surrounded by the extensive calcareous valley mire of Cors Erddreiniog, which overlies limestone and protects the lake against nutrient enrichment, resulting in water of high quality. Hedgehog stonewort Chara pedunculata and the rare rugged stonewort C. rudis have been recorded at this site.

  • The Anglesey Fens complex supports the second-largest area of calcareous fens in the UK. In some parts the low vigour of Cladium accounts for the species-richness of the vegetation, but elsewhere management prevents the development of monodominant stands, enabling the persistence of communities referable to the Caricion davallianae. The juxtaposition between species-poor stands of Cladium and areas with a more diverse floristic composition and structure is widespread, with characteristically species-rich contact zones between the two. Anthropogenic disturbance is believed to have been instrumental in the develop of various facies of a CladiumMolinia community, a particular feature of the rich fens of north-west Wales.

  • This composite site includes four component fen systems supporting a diverse range of short-sedge mires, including the best and most extensive Welsh examples of NVC type M13 Schoenus nigricansJuncus subnodulosus mire and a range of communities referable to M9a Carex rostrataCalliergon cuspidatum/ giganteum mire. These are considered to be of pre-eminent importance in the UK, owing to their extent, biogeographical significance and exceptionally rich assemblage of rich-fen species. The fens are strongly influenced by the underlying Carboniferous limestone and are fed by calcareous groundwater arising from discrete springs and more diffuse zones of seepage. The alkaline fen communities often occur within complex vegetation zonations, and typical contact communities include great fen-sedge Cladium mariscus swamp, fen carr, fen meadow communities dominated by blunt-flowered rush Juncus subnodulosus (M22 Juncus subnodulosusCirsium dissectum fen-meadow) and purple moor-grass Molinia caerulea (M25 Molinia caeruleaPotentilla erecta mire) as well as a range of vegetation types broadly referable to the CladioMolinietum. Gradations to unimproved calcicolous and neutral grasslands also occur. The characteristic mixture of southern and northern floristic elements includes a wide range of nationally or locally scarce species, including fly orchid Ophrys insectifera, narrow-leaved marsh orchid Dactylorhiza traunsteineri, marsh helleborine Epipactis palustris, lesser clubmoss, Selaginella selaginoides and slender sedge Carex lasiocarpa. Examples of M13 mire within Anglesey Fens which are strongly influenced by the discharge of calcareous groundwater provide the sole north Wales locus for the Annex II species 1044 Southern damselfly Coenagrion mercuriale.

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

  • 1013 Geyer's whorl snail Vertigo geyeri

    Cors Erddreiniog and Waun Eurad represent Geyer’s whorl snail Vertigo geyeri in north Wales. The site contains one of the largest known populations of V. geyeri in calcareous fen at low altitude.

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.