Climate change affects individual organisms and their performance capacity, thereby eliciting drastic changes in the composition and function of ecosystems. Based on the observation that the thermal tolerance of individuals and their populations vary depending on latitude and associated temperature means and variability, knowledge of the physiological mechanisms underlying thermal tolerance in organisms from different populations will support predictions of the effect of climate change on organismic up to ecosystem levels. Previous studies on different lugworm populations (Arenicola marina) have shown that oxygen supply versus demand are most crucial in thermal adaptation and limitation.In this talk data from previous studies of the oxygen limitation of thermal tolerance in lugworm populations from a wide latitudinal regime ranging from the Atlantic, North Sea up to a sub-polar population of the White Sea will be presented. In addition, studies of the temperature dependence of ventilatory peristalsis, of oxygen consumption, energy metabolism as well as growth performance have shown a clear dependence of performance parameters of A. marina on seasonal and latitudinal conditions. Currently, studies of the dependence of performance capacity of different A. marina populations on temperature dependent oxygen supply are underway. The implications of these results for the different populations in the context of climate change will be discussed.