RAMSAR CONVENTION ON WETLANDS OF INTERNATIONAL IMPORTANCE
CORSYDD MÔN A LLYN
ANGLESEY AND LLYN FENS
(Isle of Anglesey & Gwynedd)
Cors Goch, Cors Erddreiniog, Cors Bodeilio, and Cors y Farl on the Isle of Anglesey and Cors Edern and Cors Geirch on the Llyn Peninsula (Gwynedd) comprise an internationally important suite of base-rich fens, a rare wetland habitat type which has undergone large scale decline in the British Isles. While the base-rich fens of the Broadland district of East Anglia constitute their closest biological counterpart on the British mainland, the oceanic climate of north-west Wales results in the presence of a unique assemblage of northern and southern floristic elements. The six component sites share similar physical, chemical and vegetational features but differ in their associated rarities of flora and fauna. The composite site qualifies under Ramsar criterion 1d as an example of a type of wetland which is rare and unusual in the biogeographic region and under criterion 2b as it is of special value for maintaining the genetic and ecological diversity of the region because of the quality and peculiarities of its flora and fauna.
All six wetlands occupy former lake basins which have mostly infilled with marl and peat deposits, although in the cases of Cors Goch and Cors Erddreiniog open water lakes persist. Calcareous springs from limestone aquifers (or apparently in the case of Cors Geirch and Cors Edern from shelly glacial drift) irrigate the fens and lead to a distinctive vegetation of black bog rush - blunt flowered rush Schoenus n/gricans - Juncus subnodulosus hummocks which is rich in plants such as narrow leaved marsh orchid Dactylorhiza traunsteineri, fly orchid Ophrys insectifera, common butterwort Pinguicula vulgaris, long stalked yellow sedge Carex lepidocarpa and the moss Scorpidium scorpioides. In lower lying areas, swamp vegetation dominated by stands of great fen sedge Cladium mariscus, tufted sedge Carex elata and slender sedge Carex /as/oca/pa is characteristic. These fens are notable as the best Welsh sites for stoneworts (large freshwater algae which precipitate lime deposits and contribute to the deposition of marl) such as dwarf stonewort Nitella tenuissima.
The fauna of these fens reflects the very specialised nature of the habitat and includes rarities such as the marsh fritillary Eurodryas aurina, southern damselfly Coenagrion mercuriale, the soldierfly Stratiomys chamaeleon, the fly Acrometopia wahlbergi, medicinal leech Hirudo medicinalis and Geyer's whorl snail Vertigo geyeri. These sites are also used by water voles Arvicola terrestris, otters Lutra lutra, marsh harriers Circus aeruginosus, hen harriers C. cyaneus, skylark Alauda arvensis and lapwing Vanellus vanellus.
These fens have a long history of low intensity human use, notably extensive grazing, occasional burning and manual peat cutting, which has maintained and even enhanced the biological interest. In recent years many fens have deteriorated either as a result of intensive drainage and eutrophication (nutrient enrichment) or through the abandonment of traditional management. Many of the remaining sites are owned and managed by conservation agencies, including Cors Erddreiniog National Nature Reserve (NNR), Cors Bodeilio NNR, Cors Goch NNR (the latter owned and managed by the North Wales Wildlife Trust) and Cor Geirch NNR.
Countryside Council for Wales December 1997