The project faces the problem of handling complexity in the microbial part of the marine pelagic food web. The basic idea is that there is a generic structure created by the interactions between three fundamental life strategies - competition, defense and predation/parasitism. This generic structure links the life strategies to central system features such as biodiversity, biogeochemistry, population dynamics and evolution. The structure repeats itself and excert control over phenomena from microdiversity within prokaryotic species to basin scale biogeochemistry. It thus it thus creates self-similarity as in fractal theory, generating complexity and intricate patterns at many levels from simple rules. The project has a theoretical part where individual based models will be used to represent life strategies, adaption and evolution at the cell level - allowing microbial diversity to evolve as a product of the models. The theoretical work will be challenged with experimental work at two levels: the effect of host-virus interactions on biodiversity within microbial communities, and the effect of predation on structuring the balance between communities of osmotrophic microorganisms (bacteria and phytoplankton).