Micro-hydrological and micro-meteorological controls on survival and population growth of the whorl snail Vertigo geyeri Lindholm, 1925 in groundwater fed wetlands

Vertigo geyeri is a rare, tiny species of mollusc, living in calcareous, spring fed wetlands. It is considered to be threatened within the EU community; therefore it is protected under Annex II of the EU Habitat Directive (92/43/EEC). This snail has very specific micro-habitat requirements, which up to now were largely unknown. This study was initiated to provide more information on the detailed micro-hydrogeological and micro-meteorological requirements for this microscopic species in order to manage their future existence on Pollardstown Fen, Ireland and at other sites. The micro-habitat of the snail was studied during an extensive research project carried on Pollardstown Fen in Ireland during the period 2002–2005 being the first national (and possibly international) study of that scale. The results show that high relative humidity (above 80%) and close proximity to a phreatic water surface (approximately 0.1 m below ground surface) are the most important factors for maintaining populations of the snail.