Que conclure de neuf années de suivi d’une population de Vertigo de Des Moulins Vertigo moulinsiana (Dupuy, 1849) ?

The presence of the Desmoulin’s whorl snail Vertigo moulinsiana (Dupuy, 1848) justified the inclusion of the “marais de la Grenouillère” site in the Natura 2000 network and motivated the monitoring of the population of this snail, which is listed in Annex II of the Habitats-Fauna-Flora Directive. Monitoring of the species was carried out over nine years using a non-invasive protocol. The data were processed using appropriate statistical techniques. The fluctuation in abundance of Desmoulin’s whorl snail is low at the site level, but varies between transects. The variability of the abundances recorded has an impact on the precision of the estimates and does not allow us to conclude on the conservation status of the species on the site. Indeed, the species is capable of restoring its abundance from one year to the next, even when numbers are very low. The search for explanatory factors does not make it possible to say which of the measured variables has the greatest influence on the species, insofar as their significance changes according to the monitoring years. The relevance of the monitoring is discussed and perspectives are proposed in order to establish a new adapted protocol.