Reduction in the distribution of the lancT snail Thebapisana in the Tenby area, Dyfed Robert H. Cowie The land snail Thebapisana (Miiller) is widespread and abundant in coastal regions of the Mediterranean. Its range extends up the Atlantic coasts of Spain, Portugal, France and Belgium. In Britain it is restricted to a small number of colonies in the south-west (Kerney 1976), some of which exhibit unique shell pattern characteristics (Cowie 1984). Cowie (1982) surveyed these British localities, paying special attention to the detailed recording of the distribution in and around Tenby, South Wales. This is the largest British colony and lies within the boundaries of the Pembrokeshire Coast National Park. The only detailed account of molluscan distributions in the Tenby area is that of Stubbs (1900). The present paper, presenting the results of the survey of T. pisana, thus updates the record for this species. Reasons for the local distribution of T. pisana, and changes in it since the turn of the century, are discussed. Photographs of all the localities mentioned are available in Cowie (1982), with extended discussion of the origin and distribution of T. pisana in the British Isles. The Survey The whole coastline from Manorbier Bay (SN 055 977) to Wiseman's Bridge (SN 147 063) was Fig. 1 Map showing the Dyfed localities mentioned in the text, excluding Stackpole Warren. Urban areas are shaded black. searched, with the exception of the section fenced off by the Ministry of Defence at Old Castle Head (SN 073 969 to SN 082 974) (Fig. 1). No live specimens or dead shells were found at Manorbier or Penally, and only one empty shell was found (at Giltar Point) between Manorbier and the Tenby Burrows (all localities at which Stubbs (1900) found T. pisana). T. pisana was present on parts of the Burrows and in Tenby itself; these colonies are described in detail below. On Caldey Island it was abundant (about 100 snails per sq m in July 1979) on the dunes behind Priory Bay, but only three live specimens were seen on the sloping sands behind Sandtop Bay, and none on the south side of the island (cf. Stubbs 1900; Wintle 1925). T. pisana was found at two further localities in Dyfed. North of Tenby, at Saundersfoot, a locality quoted by previous authors including Stubbs (1900), only two very small colonies remained, both in patches of vegetation of only a few square metres at the edge of the beach. One of these (SN 138 051) was at the top of the stony upper beach, beside the garden wall of a modern apartment block. The other (SN 140 055) was between the beach and the coast path, with a large unmetalled car park adjacent. Only about 20 snails were ever seen at either site. West of Tenby, a rather sparse but widespread colony was observed on the dunes at Stackpole Warren (SR 978 943) (Fig. 2). This colony was recorded originally by Oldham (1928), by Kerney (1976) as extant after 1950, but not by Deblock (1962) who also surveyed this area. At Tenby all localities mentioned by Stubbs (1900) were investigated, as were other areas which seemed suitable for T. pisana. Fig. 3 indicates where T. pisana was found. Although absent from the north- and east-facing sides of Castle Hill, large numbers (up to about 180 adults per sq m Cowie 1982) were present on the south-facing side in the areas of rough vegetation beneath the mowed area which covers the top of the Hill. This was similar to the situation described by Stubbs. The snails were often associated with the umbellifer alexanders (Smyrnium olusatrum L.), as they are elsewhere at Tenby (Fig. 4). Similarly, snails were only found on the south-west side of St. Catherine's Rock, the
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