Inter-annual climate variability and zooplankton: applying teleconnection indices to two deep subalpine lakes (Lake Maggiore and Lake Garda)

In recent years, increasing interest has been shown on impact of inter-annual climate variability to zooplankton. Especially in North American great lakes, and in the large subalpine lakes north of the Alps, research has focused on impact of NAO-derived indices on biomass, population density and phenology of zooplankton. Such indices were successfully applied to explain inter-annual variations in zooplankton and phytoplankton seasonal dynamics.In large, deep lakes south of the Alps, however, the link between large-scale climatic indices appeared in most cases weak, and attempts to link such indices to interannual variations in limnological parameters and plankton seasonal dynamics did not result into clear patterns to justify common forcing. A recent study, however, analysed five teleconnection patterns potentially important for the interannual climate variability over the Mediterranean region and southern Europe. Among these indices, the East Atlantic pattern and the Eastern Mediterranean Pattern showed a clear relationship with the variables directly connected with the winter climate and limnological variables of Lake Garda, the largest Italian subalpine lake, tightly connected with phytoplankton development through cascading effects.We extended the same approach to zooplankton of both Lake Maggiore and Lake Garda, the two lakes located at the most western and eastern sides of the southern subalpine region. We selected a time frame during which changes in trophy could be ruled out, focusing on Daphnia, the large filter feeder which has the strongest impact on lake water transparency. Patterns obtained from the two lakes were quite consistent, indicative of a clear link between interannual climate fluctuations and the phenology and abundance of Daphnia. Overall, the results suggested that other, so far neglected, large scale atmospheric modes of variability might be worth of being investigated to detect, and predict, impact of climate change on freshwater ecosystems over regional scale.