Action plans for two endangered snail species in the canton of Bern
A portrait of two habitat specialists
Vertigo geyeri has a reddish-brown, shiny shell. The mouth area is equipped with four characteristic teeth. Pupilla alpicola is somewhat larger, the mouth is toothless and the shell surface is heavily striped. What the two habitat specialists have in common is that they live in the permanently moist litter and moss layer of calcareous fens (sometimes also transition bogs) and often on just a few square metres. Due to their size and limited movement rate, the two to three millimetre small snail species are very susceptible to changes in their habitats. Cultivation abandonment and intensification, scrub encroachment and reed encroachment, as well as increased periods of drought due to progressive global warming, are putting pressure on the few remaining populations. According to the Red List of Molluscs of Switzerland, Vertigo geyeri is classified as "Critically Endangered" and Pupilla alpicola as "Endangered".
The search for a needle in a haystack
As part of the development of the action plans, all known records of the two species in the canton of Bern were checked. Quite a challenge with such small and hidden species! Our approach was based on the FFH method, as Vertigo geyeri is also a strictly protected species in the EU under the Flora-Fauna-Habitat Directive and is regularly monitored. Initial doubts about the detection method using "hand catches" quickly disappeared: The tiny animals could actually be found quite reliably (with a little patience and practice). For this purpose, the moist litter and moss layer in the suspected habitat areas was scanned with the hands. Crawling snails can stick to the palms of the hands with their soft bodies and can be identified directly in the field using a good magnifying glass. The population densities per survey area were determined by preparing and analysing additional litter samples. For this purpose, litter and moss were taken from randomly selected sample areas, washed several times, sieved and all enclosures counted and determined under the binoculars. These survey data were used to draw conclusions about the colonised microhabitat and the predominant vegetation. Using an evaluation scheme, the status of the populations could be assessed, causes of endangerment recognised and possible support measures derived. A nice side effect: during the search on all fours, several other occurrences of highly endangered snail species (e.g. Vertigo substriata , Vertigo angustior and Vertigo antivertigo) were confirmed or newly discovered!
Encouraging balance and outlook
Three populations of Vertigo geyeri and one population of Pupilla alpicola were confirmed in the canton of Bern. Due to their hidden way of life and the increased frequency of extreme events in recent years (dry periods, flooding), this is a very pleasing result for these naturally rare species. Especially as some of the records date back many years. In the next phase of the project, the site-specific causes of endangerment (above all advanced reed encroachment) are now to be mitigated by adapting management. To achieve this, we are dependent on good cooperation with the farmers. If these measures are well coordinated, other and supposedly more attractive target species of nature conservation, such as the Scarce Large Blue and Dusky Large Blue, can also benefit.
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