Adaptive processes linked to overall metabolism were studied in terms of oxygen consumption andammonia excretion in each of three self-contained krill populations along a climatic gradient. In the Danish Kattegat,krill were exposed to temperatures which ranged from 4°C to 16°C between seasons and a vertical temperaturegradient of up to 10°C during summer. In the Scottish Clyde Sea, water temperatures varied less between seasonsand the vertical temperature gradient in summer was only 3°C. Temperatures in the Ligurian Sea, off Nice, wererelatively constant around 12-13°C throughout the year, with a thin surface layer (20-30 m) of warm waterdeveloping during summer. The trophic conditions were rich in the Kattegat and, particularly, in the Clyde, butcomparatively poor in the Ligurian Sea. Oxygen consumption increased exponentially with increasing experimentaltemperature, which ranged from 4°C to 16°C. Overall respiration rates were between 19.9 and 89.9 µmol O2 g-1dry wt h-1. Krill from the Kattegat, the Clyde Sea, and the Ligurian Sea all exhibited approximately the same level ofoxygen consumption (30-35 µmol O2 g-1 dry wt h-1) when incubated at the ambient temperatures found in theirrespective environments (9°C, 5°C, and 12°C). This indicates that krill adjust their overall metabolic rates to theprevailing thermal conditions. The exception to this were the respiration rates of Ligurian krill from winter/spring,which were about twice as high as the rates from summer krill despite the fact that the thermal conditions were thesame. This effect appears to result from enhanced somatic activity during a short period of increased food availabilityand reproduction. Accordingly, krill appears to be capable of adapting to both changing thermal and trophicconditions, especially when nutrition is a limiting factor in physiological processes.