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.