Unicellular organisms are the driving forces in shallow pelagic ecosystem functioning. Measurement of bulk enzymatic activity in water samples is a good proxy for the metabolic activity of planktonic communities. However the basis to understand how such ecosystems function and how planktonic communities react on natural and anthropogenic changes is detailed knowledge on how each functional unit (species) of the plankton community functions. Such knowledge will allow to understand how each component (species) contributes to the bulk community functioning and more important how changes in ecological conditions will change the community structure and subsequently the ecosystems functioning. So far such detailed analyses are not systematically undertaken. In this project we will achieve species resolution in metabolic analysis and understand the respective lifestrategies that make the most prominent phytoplankton species successful competitors in the P-limited system of the northern Adriatic (NA). We chose the NA as a well investigated and understood marine shallow ecosystem. This project investigates the metabolic adaptations to P-limitation as they are the most prominent adaptation in the NA. We will concentrate our investigations on microphytoplankton as it is taxonomically well defined and accesible to our research teams expertise and range of methods and as our preliminary results show the microphytoplankton to be the dominating component of the plankton community in the NA. Our preliminary research did uncover a variety of mechanisms that allow microphytoplankton to thrive in steep ecological gradients and generally P-limited conditions. A combination of modern and classical methodologies (ecology, oceanography, cell biology, advanced microscopy, taxonomy, phylogenetic analysis, molecular biology, biochemistry) as well as a comprehensive ecological (long term) database for the region will allow us to uncover the complex set of microphytoplankton lifestrategies.