Area: 68.1 hectares.
Description and Reason for Notification:
Rock Dunes lies on the eastern side of the Camel Estuary, opposite Padstow on the North Cornwall coast. The base rock is Devonian Slate overlain by wind blown calcareous sand which supports an extremely rich flora. Daymer Bay is of considerable geological interest.
Biological
The formation of new embryo dunes since the 1920s has provided a rare opportunity for early successional studies of this type of habitat. In addition, Brea Hill at the northern end of the dune system supports species-rich, unimproved calcareous maritime grassland.
Strandline vegetation is restricted to scattered sea rocket Cakile maritima, annual sea-blite Suaeda maritima and the nationally rare sea spurge Euphorbia paralias. The embryo dunes are dominated by the salt tolerant dune builder sand couch Elytriga juncea. Further inland, as salt levels decrease, marram grass Ammophila arenaria becomes dominant with frequent common cornsalad Valerianella locusta, wild carrot Daucus carota and Yorkshire-fog Holcus lanatus. There is occasional sand sedge Carex arenaria, and yellow-wort Blackstonia perfoliata, a species of limited distribution in Cornwall. In addition the national rarities Portland spurge Euphorbia portlandica and dense silky-bent Apera interrupta occur.
Between these new dunes and the established dunes is an area of more stable sand where the mosses Bryum capillare, Bracythecium albicans and Syntrichia ruralis are abundant. This community is succeeded by established dune turf dominated by red fescue Festuca rubra with frequent Yorkshire-fog and abundant wild thyme Thymus polytrichus and kidney vetch Anthyllis vulneraria. The locally distributed pyramidal orchid Anacamptis pyramidalis thrives here as does the nationally rare grey hair grass Corynephorus canescens. Of particular importance is the presence of a strong population of balm-leaved figwort Scrophularia scorodonia, a threatened species of national importance. Scattered throughout the established dunes are pockets of wild privet Ligustrum vulgare and blackthorn Prunus spinosa dune scrub.
Brea Hill supports a calcareous maritime community dominated by red fescue but with scattered marram grass on blown sand on the seaward side. Wild thyme, kidney vetch, lady’s bedstraw Galium verum, carline thistle Carlina vulgaris and the locally rare viper’s-bugloss Echium vulgare are among a rich flora.
This rich calcareous flora at Rock Dunes supports a diverse invertebrate fauna. Of particular note is the large mollusc community with a number of characteristic dune species. These include Cochlicella acuta, Candidula intersecta, Cernuella virgata and Hellicella itala. The numerous butterflies on this site include a large breeding population of marbled white Melanargia galathea. In addition, grayling Hipparchia semele and silver-studded blue Plebejus argus have been recorded.
Geological
Daymer Bay contains excellent exposures of the Harbour Cove slates (U. Frasnian) and Polzeath Slates (L. Fammenian). Both units are richly fossiliferous which is unusual in this area. The Harbour Cove Slates contain useful palaeocurrent indicators and are consistent with a deep water environment. This is a key palaeontological site whose rich fauna allow precise dating for local Devonian sedimentary sequences.