Étude de l’habitat et des exigences écologiques du Vertigo geyeri Lindholm, 1925 dans le Massif jurassien

The Geyer’s whorl snail (Vertigo geyeri Lindholm, 1925) is a very small mollusc (< 2 mm), registered to the Habitat Directive. Franche-Comté region in France is situated on the occidental limit of its distribution in mainland Europe and is hosting the main population in the country. Within a second year master internship, this study was conducted to characterize the snail’s habitat and environmental requirements, through the analysis of botanical and malacogical associations, and main environmental parameters. Therefore, 32 sites have been sampled in 2016 and 2018 in the Jura Mountains. The wet sieving technique has been used for the malacogical sampling, in addition to a botanical survey (vascular plants and mosses). We were able to associate the snail with alkaline fens with marsh clover and mosses from the Amblystegiaceae family (Caricenion lasiocarpae), with Menyanthes trifoliata L. and Scorpidium cossonii Hedenä as structuring species. These wetlands are usually open, with important hydraulic network, sparse vegetation and nutrient limited soil.