1014 Narrow-mouthed whorl snail Vertigo angustior
Description and ecological characteristics
The tiny narrow-mouthed whorl snail Vertigo angustior is found primarily in marshy ground of high, even humidity, with flowing groundwater, but subject neither to deep or prolonged flooding nor to periodic desiccation. It requires unshaded conditions and lives amongst short vegetation, composed of grasses, mosses or low herbs, that is quickly warmed by the sun. The vegetation may be grazed. In the British Isles it has been found in wet base-rich meadows, in coastal marshes, dune slacks and maritime turf, and in depressions within limestone pavement; several of these habitats are listed on Annex I of the Habitats Directive. In the UK the largest known population is found where freshwater seeps onto the upper edges of a saltmarsh in south Wales. However, elsewhere in Europe calcareous fen is the species’ most typical habitat. Because of its specific microhabitat requirements, the species is often restricted to a narrow zone around wetlands, only a few metres wide.
Vertigo angustior flourished in post-glacial conditions, but climatic change led to a dramatic contraction of its range, and the species is vulnerable to drainage or afforestation of the sites where it survives. Like all Annex II Vertigo species, it is highly dependent on maintenance of existing local hydrological conditions.
European status and distribution
Vertigo angustior is widely but locally distributed in central Europe northwards to southern Norway and Sweden but is considered threatened in most countries. The fossil record shows that it was once much more widespread in Europe at the end of the last Ice Age.
UK status and distribution
In the UK, Vertigo angustior is known from eight widely scattered localities in England, Wales and Scotland.
Site selection rationale
Sites have been selected to encompass the diverse range of habitat types in which V. angustior is found (saltmarsh, base-rich fen, and limestone pavement), and to represent its geographical range. The selected sites all have strong populations of the species and ecological conditions considered to be particularly favourable for its survival. The known site in south-west Scotland was not selected as it is threatened by natural erosion; a second Scottish site on the north-east coast was discovered during 2000 (Kerney 2002).
Carmarthen Bay Dunes/ Twyni Bae Caerfyrddin
East Wales, West Wales and The Valleys
Carmarthen Bay Dunes represents narrow-mouthed whorl snail Vertigo angustior in south Wales. Whiteford Burrows contains by far the largest known population of this snail in the UK. The snail occurs at this site in areas of freshwater seepage at the junction between sand dune and saltmarsh habitat, where horse grazing maintains the open conditions this species requires.
North Eastern Scotland
Species occurrence description not yet available.
Morecambe Bay Pavements
Morecambe Bay Pavements represents narrow-mouthed whorl snail Vertigo angustior in north-west England, near the northern limit of its range in the UK. Gait Barrows supports strong populations of the species in mossy clint tops of Annex I habitat 8240 Limestone pavements at transitions to woodland, an unusual habitat for the species.
Norfolk Valley Fens
Norfolk Valley Fens represents narrow-mouthed whorl snail Vertigo angustior in East Anglia. At Flordon Common a strong population occurs in flushed grassland with yellow iris Iris pseudacorus maintained by light grazing.
North Antrim Coast
The North Antrim Coast supports the only known living population of narrow-mouthed whorl snail Vertigo angustior in Northern Ireland. The species was rediscovered in 2002 at two separate localities on the site. Both support strong populations of the species in areas of ideal habitat – i.e. tall, lightly-grazed, damp grassland – and it is likely that they have persisted for many decades.
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