One of the most serious challenges for humankind this century will be to understand how climate change (past, present and future) influences life in the oceans. It is known that marine phytoplankton carry out almost half of the global net photosynthesis of the planet. Therefore it will be essential to determine how climate change alters microbial metabolism. However, the integration of cell biology and genomics into oceanographic research is not sufficiently developed, even though biological (and especially microbiological) processes are fundamental for maintaining a functional biosphere.This project addresses the application of a novel molecular approach using genomics and metagenomics to elucidate metabolic activities under different conditions in the ocean in various groups of photosynthetic prokaryotes and eukaryotes. These techniques will also allow the rapid identification of candidate genes and facilitate the association of genes with specific metabolic and regulatory functions in different organisms spanning hundreds of millions of years of evolution. The initial phase of the project will investigate unicellular cyanobacteria using full genome microarrays analysis (outgoing). In a second phase, genomics studies will be done in diatoms, unicellular eukaryotes (return).The novelty of the proposed research lies in its interdisciplinary approach linking oceanography with cell biology and genomics. A key novel aspect of the proposal is the application of a comparative approach to very different groups of photosynthetic organisms, which will allow us to contrast the strategies of responses to environmental changes between them. This will improve our knowledge of the crucial roles marine microorganisms play in maintaining the well being of our planet. The successful implementation of the project will result in a substantial transfer of expertise from a world wide-leading centre in marine biology to the applicant and his team on return to a European institute.