Lake Baikal is the largest freshwater lake on earth. It hosts a highly diverse community including numerous endemic species at all trophic levels. At the base of the food web, spring phytoplankton bloom is typically dominated by large endemic diatom species, which begin blooming right under the ice. Understanding the interaction between climatic and biotic drivers of the plankton community in Lake Baikal is crucial for predicting how rising mean annual water temperature and shortening of the ice-covered period, associated with climate change, will impact the base of the food web. We used a seasonally forced phytoplankton-zooplankton model, differentiating winter and summer phytoplankton assemblages, to investigate the interplay of length of the ice-covered period with phytoplankton-zooplankton interactions.
Results/Conclusions
Along decreasing length of the ice-covered period, model predictions shift from pronounced spring phytoplankton blooms every year for extensive periods of ice-coverage, to a failure of spring phytoplankton bloom every other year at intermediate length of the ice-covered period, until under-ice blooms disappear completely. High spring phytoplankton blooms thereby correlate with low zooplankton biomass at the end of the preceding year. Especially the two year cycles at intermediate length of the ice-covered period are characterized by low zooplankton, high spring bloom in one year and high zooplankton, low spring bloom the following year. Cluster analysis on longterm data from Lake Baikal support model predictions on the interactive effect between abiotic and biotic forcing on spring bloom phytoplankton development. Our results suggest that a shortening of the ice-covered period would severely harm the endemic, primarily springtime algae, thereby favouring cosmopolitan, primarily summertime phytoplankton species.