Can you count on counting? Retrieving reliable data from non-lethal monitoring of micro-snails

Using non-lethal methods is especially important for the monitoring and conservation planning of endangered species and their habitats. The goal of this study is to check whether the current method of monitoring endangered micro-snail populations by soil sampling, which involves killing the snails and altering their microhabitat, could be replaced by a non-lethal method. The invasive and time-consuming soil sampling and analyzing is compared with searching the individuals by eye. Research was conducted in moist sedges meadows and seasonally inundated wetlands in western Poland and focused on two species of micro-snails differing in biology, i.e. Vertigo moulinsiana (a climbing species) and Vertigo angustior (a litter-dwelling species). Both vertiginid species are listed in the Annex II of the EU Habitat Directive and included in the IUCN Red List of Threatened Species. The results showed a significant correlation between the total number of individuals searched by eye and collected from soil samples of V. angustior and V. moulinsiana. Results of this study indicate that monitoring micro-snails by searching individuals by eye is feasible and may reduce further pressure of killing individuals of endangered species. Limitations of this method should however be taken into account - especially its inaccuracy in estimating the absolute abundance of the studied species.