Relationships among recent Alpine Cladocera remains and their environment: Implications for climate-change studies

Our objective was to assess the potential of Cladocera from mountain lakes for climate reconstruction. We related Cladocera from surface sediments of Alpine lakes (1,502-2,309 m asl) to 29 abiotic environmental variables using statistical methods. The environmental dataset included water chemistry, lake depth, and bi-hourly water-temperature logs, which were used to assess mean monthly water temperatures, dates of freezing and breakup, spring and autumn mixing. We found 14 different Cladocera of the families Bosminidae, Daphniidae, and Chydoridae. Lakes without Cladocera (eight lakes) were cold and/or ultra-oligotrophic, whereas lakes with planktonic and littoral Cladocera (19 lakes) were warmer and/or less oligotrophic. Lakes with only littoral Cladocera (18 lakes) had intermediate water temperatures/trophy. Changes in Cladocera assemblages were related to changes in climate, nutrients, and/or alkalinity. We found a climate threshold at which Bosminidae disappeared in 95% of the lakes. For climate-change research, we propose studying Cladocera along transects that include climatic thresholds.