Nejstgaard, J. C. ... et. al.-- 2012 Ocean Sciences Meeting, 20-24 February 2012, Salt Lake City, Utah, USAIn April 2008 a cross-disciplinary group of 24 scientists from 7 countries conducted a mesocosm experiment using 7x11 m3 in situ enclosures with natural seawater on the Norwegian west coast. A controlled gradient of increasingly mono-specific blooms of the diatom Skeletonema marinoi was created, and used to investigate chemical signaling, metabolomics, food quality, copepod reproduction and plankton development. We summarize intriguing results spanning from comprehensive studies of in situ metabolomics to food web dynamics using a suite of novel and classical approaches. With the advent of new in situ targeted analytical approaches, we argue that mesocosms are excellent tools to study complex food web interactions including chemical signaling and net nutritional effects on the plankton ecosystemsPeer Reviewe