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Title: The Ecology of Four Scarce Wetland Molluscs
Author: A Watson
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1638, Representation ID: 565, Object ID: 2745
In 1995, the United Kingdom (UK) Biodiversity Action Plan listed four wetland molluscs of Red Data Book (RDB) status that required urgent conservation measures to prevent further reduction in their distribution: Segmentina nitida (Muller 1774), Anisus vorticulus (Troschel 1834), Valvata macrostoma (Morch 1864) and Pisidium pseudosphaerium (Schlesch 1947). All four typically occur in drainage ditches of large lowland grazing marshes of southern Britain and have shown marked decline in range, particular Segmentina nitida. However, despite their relative rarity, little is known of their ecological requirements, the reasons behind their decline, nor the management measures that might benefit their numbers. This study used a blend of large-scale surveys, small-scale surveys and field experiments to assess likely biotic and abiotic effects on distribution and abundance. Each of the RDB molluscs occurred in ditches with different ecological characteristics. Segmentina nitida occurred in shallow calcareous ditches choked with mainly emergent plants and occurred in locations with abundant amphibious vegetation; these features typified ditches at the advanced stages of vegetation succession. Ditches with Valvata macrostoma were dominated by floating plants but this species reached its greatest numbers within the emergent stands. Anisus vorticulus was recorded in less calcareous ditches than the other two snails, and typically occurred in channels with a high diversity of aquatic plants. Pisidium pseudosphaerium occurred in ditches with similar vegetation to both Valvata macrostoma and Anisus vorticulus, which were at a comparatively less advanced stage of vegetation succession. Changes in the ecological character of drainage ditches can be attributed to the intensification of agriculture on grazing marshes, which has led to inappropriate ditch management, decreasing connectivity between ditches and increasing eutrophication. Based on work in this thesis, rotational management of ditches that maintained a full sequence of vegetation succession throughout a given grazing marsh would benefit all the target RDB molluscs and their associated assemblages. In addition, reduced agro-chemical use on grazing marshes is likely to assist the maintenance and recovery of three of the RDB species.
Publisher: Environment Agency
Subject Keywords: WetlandsDrainageMolluscaNature conservationDitchesEutrophicationMarshesNature conservation
Taxonomic Keywords: Anisus vorticulusValvata macrostomaSegmentina nitidaPisidium pseudosphaerium
Extent: 217
Total file downloads: 351

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