An investigation of the eukaryotic picoplankton community in the German North Sea by different methods

Picoplanktonic organisms are ubiquitous around the world and are able to dominate biomass, production, and metabolic activity in diverse regions of the oceans. It is suggested that they perform important and basic functional roles in the marine ecosystem, although many of their ecological functions and characteristics remain unknown. For example, the reaction of picoplankton to anthropogenic influences, such as eutrophication, pollution and climatic change, or the spatial and temporal differences among clades and ecotypes have not been determined yet. This thesis examined the identity and ecological abundance of picoeukaryotes in the coastal waters of the German Bight on a weekly frequency over a 17-months period by using diverse currently existing methods. Special emphasis was placed on the comparison of these methods and one species, Micromonas pusilla (Mamiellales, Prasinophyceae), which is the best-studied and possibly most abundant phototrophic picoeukaryote