Meganyctiphanes norvegica (M. norvegica) is a krill that belongs to the group of crustaceans. Krill can be found in a wide range of environments, which are characterised by different conditions in terms of temperature, depth, light, and nutrition. The fact that M. norvegica can be traced from the Arctic to the Mediterranean sea, indicates that they possess mechanisms to adapt to a wide range of environments. These mechanisms make krill an organism suitable for studies on ecophysiological optimisation in different climatic and trophic environments. Under the PEP project, a multidisciplinary group of experts in physiology, ecology, genetics and acoustics were assembled in order to study the mechanisms that enable M. norvegica to be adaptive to different conditions. The study took place in three sites where colonies of M. norvegica live in cool (Clyde sea, Scotland), warmer (Ligurian sea, France) and thermally variable (Kattegat, Denmark) environments. The project showed that krill populations differ from region to region. These differences lie in their nutritional habits, lipid accumulation and composition, developmental and reproductive cycle, as well as in their metabolic rates. Moreover, the examination of mitochondrial and nuclear DNA revealed three distinct genetic pools. In these three places the population layers were different. Consequently, it was found that M. norvegica has the ability to change some of its "living parameters" according to the climatic conditions. Since krill are an important link in the marine food chain, the knowledge gained regarding the behaviour of krill under various conditions can be used for commercial and further research purposes For example, the results can be used for better management of local fisheries, and the innovative combination of ecophysiological and genetic techniques can be applied in studies for other zooplankton species.