Acidification, deoxygenation and rising water-temperatures in our oceans are becoming an omnipresent issue for most marine organisms. Abiotic factors play an important role in the trophic system and slight changes might already have significant effects on various trophic levels. Not only larger animals like fish and marine mammals suffer from temperature and pH-level fluctuations, but also smaller organisms such as plankton are challenged coping with them. These alterations may affect the organism’s fitness and ability to adapt to certain environmental changes. On a cellular level this effect is expressed as a stress response, which can have an extensive impact on the organism’s metabolism and oxidative state (generation of reactive oxygen species (ROS)). The overall aim of this thesis was to understand how a temperate plankton community copes with future multi-stressors in terms of plasticity as a result of an increasing temperature (global warming) and Carbon dioxide (CO2) concentrations (acidification) of the ocean. Field samples of plankton, mostly containing copepods of the genus Acartia sp., were collected with a 150 μm plankton net at the Helgoland Roads and shortly after exposed to different treatment-combinations of CO2 (450, 800, 1000 ppm) and temperature (5, 7, 10, 12, 15 °C) for seven days. Metabolism and four different oxidative stress indicators were analysed to determine oxidative status and possible damages of planktonic tissue and cells. Routine metabolic rates (RMR) of different CO2 treatments were very high in variability at the acclimation temperatures 10 and 12 °C, they were lower and more distinct at 7 and 15 °C and organisms had very similar RMR at 5 °C. The integrated biomarker response (IBR) model demonstrated that plankton for all CO2 concentrations were affected negatively when temperature increased. At the highest temperature, exposed organisms of the higher CO2 concentrations still responded with antioxidant defence but suffered oxidative damage to lipids. According to achieved results, it is assumed that temperate plankton of the North Sea can cope with the acidification that is predicted by the 2100 climate scenario (IPCC 2007) until reaching a certain temperature. But temperature alone can be considered a stressor and in addition to higher CO2 concentrations, organisms’ antioxidant capacity is outbalanced by lipid damage (oxidative stress), which can be presumed to have a significant impact on their homeostasis. Future studies realizing similar experimental setups as in this pilot study should improve the significance of their results by implementing repetitive collection of data.