In the PLUSDATA project we investigate the response of hydrological conditions and plankton - its diversity, occurrence, relative distribution and seasonal pattern - to inter annual climatic variation and climate trend. We, therefore, analyse long term data from Plußsee, a small deep eutrophic lake in North Germany. We identify key hydrological features and plankton signatures of climate variability and possibly long-term climate change through an exhaustive joint statistical analysis of this data set. For example, changes in plankton species diversity and their relative distribution can be due to differences in the degree of synchronous versus asynchronous responses to altering climate conditions. We look whether differences in response can be detected between more r-strategic and more k-strategic plankton organisms and which effect this has on the species diversity. Special sensitive phases are identified and are investigated in more detail. Special attention will be paid to key-stone species, and potential impacts on the food web structure and function.