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Nature in Wales


N.s. Vol. 4, no. 1/2 1985

Reduction in the distribution of the land snail Theba pisana in the Tenby area, Dyfed

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parallel to the North Cliff SN 132 010) to beyond
the boundary of Tenby (SN 128 025). Old empty
shells were found in the earth of the roadside bank
as far inland as the point where this road joins the
main road out of Tenby (about 1 km inland). Living
specimens were only found on a 20 m length of the
northern (i.e. south-facing) bank of the road,
opposite The Glebe. No more than seven were seen
at any one time.
A further, rather sparse colony was found alongside
the south side of Marsh Road, for a distance of
about 500 m opposite the County Secondary
School. Snails were found in the low vegetation (up
to about 50 cm) which extends beyond a low
Fig. 4 Theba pisana resting on alexanders.
wooden railing set back about 2 m from the road,
the area between the road and this fence being short
Discussion and conclusions
The most striking change to have taken place in the
distribution of T. pisana in mainland Britain since
previous accounts is the reduction in abundance on
the Tenby Burrows, and the apparent absence of the
species from Manorbier (last recorded by Deblock,
1962) and the cliff-tops from Giltar to Lydstep (cf.
Stubbs (1900) and Wintle (1925) who both indicated
the species in profusion on the Burrows, although
whether it was particularly abundant on the cliff-
tops was not said). Its complete absence from the
half of the Burrows nearer to Tenby itself is
certainly the result of the planting of sea buckthorn
in about 1940 (Stratton 1970). Little other
vegetation is present and it therefore no longer
provides a suitable habitat for T. pisana. The
development and increased use of the golf links has
undoubtedly also contributed to its demise in this
area. Barrett (1972) indicated how trampling of
areas of marram and cutting of the vegetation
excluded T. pisana from otherwise apparently
suitable areas in Guernsey.
Manorbier Bay is a popular beach during summer; a
large area behind the beach itself is used as a car
park, and the dunes around the Bay are heavily used
by people. This may well be significant in the
apparent extinction of T. pisana here.
There is little suitable habitat on the cliff-tops from
Giltar to Lydstep. These cliff-tops are trampled by
people, and both sheep and cattle graze right to the
edges along parts of this section of coast. Chappell
et al. (1971) showed how trampling can change the
habitat and hence the associated snail fauna; Morris
(1968) indicated similar changes due to grazing. The
short turf which results is unsuitable for T. pisana
(see Barrett 1972). Humphreys (1976) did say that
the area inhabited by T. pisana at St. Ives in
Cornwall had the appearance of a 'short, dense grass
sward', but the same area, observed in 1979 was
covered with mixed vegetation up to 50 cm high, a
relatively normal habitat for T. pisana, if not as high
as the alexanders and sea radish it is often associated
with at Tenby. It is probable, then, that increased
trampling and grazing partially account for the
extinction of T. pisana along these cliffs.
The colonies on Caldey Island are subject to
considerable human interference during the summer
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