Antarctic species possess very low metabolic rates and poor capacities to change their physiological state, thus making them extremely vulnerable to changing environmental conditions. Mitochondria are a key element in shaping whole organism energy turnover and functional capacity. In my study, the effects of rising temperature and increased seawater PCO2 on the energy metabolism were compared between various nototheniids from sub-Antarctic and cold-temperate and Antarctic waters, and between cephalopods from the Antarctic and temperate latitudes. I determined extra- and intracellular blood carbonate parameters, enzymatic capacities and oxygen consumption at whole animal and mitochondrial level and mitochondrial lipid composition and proton leak as a measure for routine metabolic rate, in order to compare their abilities for metabolic compensation towards climate change. My results showed limited aerobic capacities of high-Antarctic fish mitochondria towards the warmth and higher CO2-levels. The mitochondrial responses of cephalopods to an acute temperature rise suggest that they possess similar mitochondrial flexibilities and capacities towards the warmth as fish. Nevertheless, generally more effective capacities for acid-base regulation and larger energy reserves (lipids) in fish compared to cephalopods will putatively make them win the competition for resources over longer time-scales, when seawater temperatures and PCO2 continue to rise.