Changes in gastropod assemblages in freshwater habitats in the vicinity of Basel (Switzerland) over 87 years

Abstract

The gastropod fauna in 18 freshwater habitats (streams, rivers and ponds) in the vicinity of Basel, first surveyed in 1906/1907, was re-examined in 1994. The freshwater snail fauna changed considerably over 87 years. One species (Aplexa hypnorum) recorded in 1906/1907 was not found in 1994, most probably it had become extinct in the period between the two surveys. Ten species were found in 1994, but not in 1906/1907. Two of them could not have been recorded in the first survey: the recently invading Potamopyrgus antipodarum and Ferrissia wautieri, a species first described in 1960. In contrast to these changes a part of the gastropod species appear to have a rather constant occurrence. All ten gastropod species found in both surveys showed similar percentage of occurrence (constancy) over 87 years. Species that were rare in 1906/1907 were also rare in 1994, and species common in the first survey were also common 87 years later. Interestingly, species considered as threatened throughout Switzerland towards the end of the 20th century (Red List species) were already rare at the beginning of the century in the habitats examined in the present study. The 1994 survey provides a baseline for monitoring future changes in snail species richness and abundance as riparian restoration actions are under-way or planned at several sites in the region of Basel.