Area: 20.5 hectares.
Within an Area of Outstanding Natural Beauty. A new site which includes a Geological Conservation Review site.
Description and Reasons for Notification:
Rosemullion comprises a 2 kilometre section of coast along the northern entrance of the Helford River inlet, approximately 5 kilometres south of Falmouth. The cliffs and intertidal zone are of particular interest for their geology and marine biology.
Rosemullion Head exhibits an example of superimposed ‘cross folding’ in alternating graywackes and mudstones of the Gramscatho Beds. The structures are well exposed in the wave-cut platforms surrounding the low head-capped promontory. This site is significant in the development of ideas concerning the structural history of south-west England as it was argued by Lambert in 1959 that the folds were generated synchronously during one phase of deformation. Subsequently the pattern of deformation has been reinterpreted as resulting from the interference of structures of two separate episodes of crustal shortening. Close to tight first generation folds are present throughout the section. The attitude of these folds is modified by second generation folding which steepens and overturns the earlier structures. The second generation folds are the most conspicuous minor folds of the area and they clearly deform earlier structures. These structures are ubiquitously developed here and good examples of their interference are common.
The marine interest spans two distinct sections and it should be noted that these communities extend into the estuary beyond Mean Low Water Mark. The first, Rosemullion Head to Prisk Cove is a particularly species-rich area. The intertidal zone comprises a shingle beach extending into a bedrock platform with boulders and numerous rock pools on the lower shore, creating an excellent range of habitats.
Rosemullion Head itself is a fine example of a moderately exposed, rocky shore dominated by mussels Mytilus spp. and barnacles Balanusspp. Prisk Cove consists of vertical and steeply sloping bedrock with overhangs resulting in a high habitat diversity. The large rock pools are of national importance for their rich algal communities. An important feature of these is the abundance of seaweeds, particularly bushy wracks Cystoseira tamariscifolia and the rare southern species C. foeniculaceus, together with slender beaded coral weed Jania rubens and common coral weed Corallina officinalis. A total of fifty-five species of algae are recorded along this shore. The following are of particular interest: the brown seaweeds lambs tails Spongonema tomentosum and sea flax weed Halopteris scoparia, and four species of red seaweeds fern weed Laurencia platycephala, diamond cartilage weed Chondria dasyphylla, flattened pincer weed Microcladia glandulosa and Dermocorynus dichotoma. The latter two are rarely recorded in Britain. In addition to the algae several unusual marine species also live in these pools. The presence of maerl Phymatolithon calcareum and eelgrass Zostera marina is of particular note. These species are uncommon and are normally associated with sub-littoral regions rather than intertidal pools.
The underboulders and overhangs support a characteristic faunal association of sponges, sea squirts and decapod crustaceans which are of regional importance. They include the sponges Hymeniacidon perleve and Dysidea fragilis, the star ascidian Botryllus schlosseri and the crab Xantho incisus. The straightnosed pipe fish Nerophia ophidion also occurs under boulders.
The second area, Parson’s Beach, is a moderately exposed boulder shore. The upper and mid-shore is dominated by opportunistic algal species, but the low shore and sublittoral fringe support a well-developed seaweed community dominated by serrated wrack Fucus serratus and kelps Laminaria spp. The shore is particularly important for the well-developed underboulder communities and rich boulder interstices. The species present show a strong southern element, exemplified by the anemone Actinia fragacea. The shore is undisturbed and supports fine examples of typical south-western, intertidal communities which are of regional importance.