Organisms that belong to the pico-, nano-, and microplankton are at the base of marine food webs and are from fundamental relevance for the functioning of marine ecosystems. These three size fractions comprise bacteria, eukaryotic protists (e.g. phytoplankton or heterotrophic protozoa) and small or juvenile metazoans. Phytoplankton accounts for around 95% of the primary productivity of the ocean and is the basis of the marine food web. This energy is passed through the food web by trophic interactions. The fundamental ecological role of plankton (size fraction < 200 µm) for marine food webs makes it necessary to assess the consequences of climate change for this group of organisms. Moreover, marine plankton is very well suited to serve as an indicator of climate change, because plankton dynamics is closely cloupled to environmental conditions. Therefore, PLANKTOSENS aims at the molecular assessment of eukaryotic plankton of the size fraction < 200 µm. The data generated during the founding period will aid to identify variation in the structure and succession of eukaryotic plankton. Furthermore, the data will serve as a baseline that contributes to estimate the consequences of climate change for the base of marine food webs in Polar Regions and the North Sea.