Malacological history of Lake Annecy (France): a comparison of Late Holocene (since 4700 BC) and present mollusc assemblages
Mouthon, Jacques; Magny, Michel
published: Aug 17, 2004
An analysis of mollusc assemblages of the Younger Atlantic, the Subboreal and the Subatlantic periods (i.e. since 4700 before Christ) was carried out on the basis of 8 cores taken from the littoral zone of Lake Annecy, France. The structure and composition of these communities remained remarkably stable for several thousand years. The assemblages were dominated by gastropods: Bithynia tentaculata, Valvata piscinalis and V. cristata. Of the bivalves, only Pisidium nitidum was well represented.Comparison between fossil and present-day populations in the littoral zone revealed considerable changes in the composition and structure of the communities. Seven species have appeared recently in the lake and current assemblages are dominated by the bivalves of the Sphaeriidae family, since the development of gastropods was greatly limited by substantial regression of vegetation belts during the 20th century. The dominant species during the second part of the Holocene were replaced by Potamopyrgus antipodarum in the gastropods and Pisidium henslowanum, Dreissena polymorpha and P. moitessierianum in the bivalves. Finally, it is hypothesised that recent climatic warming rather than eutrophication is the most likely reason for the establishment and significant increase of thermophilic species, such as Pisidium moitessierianum in Lake Annecy.