Since 1999, the invasive Asian shore crab Hemigrapsus sanguineus successfully established populations along the Atlantic coastline of Europe, now reaching from the French Channel coast to the German Bight. While various studies on population development and behavior are available, the physiology of H. sanguineus and its energetic impact on the habitat are virtually unknown. We measured the oxygen consumption of H. sanguineus and of its native equivalent, the European shore crab Carcinus maenas, and assessed the energetic ecosystem impact of the invader versus the native species. Respiration rates were determined in a flow-through system at 5, 10, 15 and 20 °C, the crab´s natural temperature range in European habitats. We compared mass-specific respiration rates of mass-standardized crabs of 0.5, 5 and 10 g body mass. Small H. sanguineus specimens consumed significantly more oxygen at higher temperatures than small C. maenas. This difference was less distinct in medium-sized animals and absent in larger animals. We established species-specific models to calculate respiration rates for a crab using the individual´s biomass and the water temperature. These models were applied to the crab populations from the intertidal of the island of Helgoland (Germany) based on data from August 2014. While total population biomass of H. sanguineus was as high as 59% of that of C. maenas, population respiration and energy demand of the invader reached about 78% relative to the value for the native species. As H. sanguineus abundances are still rising, the food uptake and thus the energetic ecosystem impact of this invader will continuously increase in the future.