Little Whirlpool Rams Horn Snail (Anisus vorticulus) - Species Action Plan

A truly aquatic species, the small shell is 5mm across, in the form of a spiral disc, shaped like a ram’s horn.  It occurs in unpolluted, calcareous waters in well-vegetated marsh drains and is usually found with a number of other molluscs which are rare and vulnerable, including Segmentina nitida.
Ref 1/S13 Species Action Plan 13
Plan Author: English Nature
Plan Co-ordinator: English Nature
Review completed January 2003

Action Plan Summary

Current Status

National Status

  • This snail is local throughout its central and southern European range. In Britain living colonies have not been confirmed outside East Anglia for over ten years. The snail is listed as vulnerable in the GB Red List. 

Norfolk Status

  • Found within the Broads, North Norfolk, Old Hunstanton to Sheringham and Breckland Natural Areas. Rarer than Segmentina nitida.

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Current factors affecting the habitat in Norfolk

  • Inappropriate ditch clearance. 
  • Nutrient enrichment may be a factor, but organochlorines, heavy metals and other toxic chemicals from anti-fouling paints are almost certainly detrimental. 
  • Conversion of grazing marshes to arable farming with associated water table lowering. 

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Current Action in Norfolk

None

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Action Plan Objectives and Targets

National

  • To maintain populations at at least 15 sites 
  • Produce management advice by the year 2000 
  • Establish baseline monitoring data for all known populations by the year 2000 

Norfolk

  • Maintain population at the 4 Broads sites and at the single North Norfolk Coast site 
  • Establish if it still persists within Breckland Stanford Training Area SSSI 
  • Produce Management advice by the year 2000 
  • Establish baseline monitoring data for all known populations by the year 2000

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Management Guidance

(This guidance is a general summary; for detailed information or advice consult the references or contacts below.)

Prefers wide (>3m), comparatively deep (>1m) ditches with little emergent vegetation cover. Occurs in ditches in wet fields that flood in winter. Can tolerate high levels of filamentous algae and Lemna, and has a significant association with frogbit. Aspect and water temperature appear to be critical; the snail can be restricted to one side of a ditch, which has important implications for management.

Although this snail thrives best in areas that are lightly grazed, it can tolerate higher densities of stock than Segmentina nitida.

Red Data Book category: vulnerable. Threatened by drainage, over-frequent dredging and eutrophication.

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Key Contacts

  • General Information

Ian Killeen - ian@malacserve.demon.co.uk.

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References

Environment Agency (1998). Snails. Environment Agency Species Awareness Leaflet No 2.

Jackson, M J and Howlett, D J (1999). Freshwater molluscs of the River Waveney grazing marshes. A survey carried out during the summer of 1997. Broads Authority report (BARS 18).

Killeen, I J (1999). The freshwater snail Anisus vorticulus: 1998 monitoring survey of ditches in East Anglia. English Nature Research Report 311. Peterborough: English Nature.

Killeen, I J and Willing, M J (1997). Survey of ditches in East Anglia for the freshwater snails Segmentina nitida and Anisus vorticulus. English Nature Reports No 220.

Killeen, I J and Willing, M J (1997). Survey of ditches in East Anglia and south-east England for the freshwater snails Segmentina nitida and Anisus vorticulus. English Nature Research Report 229. Peterborough: English Nature.

Willing, M (1997). Fresh and brackish-water molluscs: some conservation issues. British Wildlife 8(3): 151-159.

Willing, M J and Killeen, I J (1998). The freshwater snail Anisus vorticulus in ditches in Suffolk, Norfolk and West Sussex. English Nature Reports No 287.

Willing, M J and Killeen, I J (1999). Anisus vorticulus – a rare and threatened water snail. British Wildlife, 10:6, pp 412-418. 

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