Understanding how climate change will affect the planet is a key issue worldwide and addressing the consequences of global warming for the biosphere has become a research priority. The rise of temperature has affected all Earth´s subsystems including the oceans. Copepods of the genus Calanus are predominant in the zooplankton biomass of the North Atlantic and the Arctic. They play a key role in marine food webs both as main primary consumers and as prey species for many commercially important species. As a response to ocean warming, a northward movement of warm-water Calanus species has been observed and C. finmarchicus appears to have declined throughout much of the North Atlantic. Calanus sp are often separated based on their size and on the geographic location of collection. As changes in temperature are expected to affect both the distribution and the size of Calanus, is clear that molecular tools for the identification of Calanus species are essential. It is also crucial to access the ecological (r ange shift) and evolutionary (population genetic / selection / genetic diversity & effective population sizes) response to climate change of Calanus. The main goal of this project is to use new molecular mnethods in combination with historical samples to address how climate change has affected the distribution and the evolutionary response of Calanus species in the North Atlantic. By developing Calanus spp as beacons of climate change, the research will contribute toward a better understanding of the inte raction between climate change and plankton communities; and a better forecasting of the changes in food web structure of the North Atlantic and Arctic Oceans. Such knowledge will be crucial for an appropriate societal response.