Phytoplankton algae form seasonal blooms which fuel aquatic systems. In variable environments like the Baltic Sea, conditions in the water support algal growth only for short periods of time. Many species enter dormancy and spend adverse conditions resting in the sediments at the sea floor. The sediments integrate individuals and species over time and form a genetic reservoir, equivalent to seed banks of higher plants. Such reservoirs are expected to function as buffers against environmental variability. Here we investigate how the diversity reservoir supports the capacity of Baltic algae to deal with environmental change. The project characterizes resting stage diversity of the benthic seed banks using modern sequencing approaches, and examines the relationship between seed banks and phytoplankton stability in lab experiments and long term data analyses. This project will contribute to a better assessment of the resilience of Baltic plankton under conditions of ongoing environmental change.