This project is situated in the field of ecotoxicology. Toxic cyanobacteria can contaminate drinking water and surface water, affecting both humans and aquatic animals. Harmful cyanobacterial blooms have already been reported in surface waters and reservoirs in Luxembourg and elsewhere, and their occurrence is expected to become increasingly severe under projected climate change. Copper (Cu) is a contaminant of concern under the water framework directive and knowledge about its toxic modes of action suggest that it could intensify the toxicity of cyanobacterial toxins in the waterflea Daphnia magna. Until recently conventional ecotoxicology has widely ignored the fact that natural populations usually face such multiple-stress conditions in nature and also that genetically diverse populations may show micro-evolutionary responses leading to genetic adaptation. This PhD project will address these knowledge gaps by determining combined and interactive effects of copper and cyanobacteria in the Daphnia magna. Using a combination of short-term life-table experiments, long-term population growth and experimental evolution studies, and biomarker and whole-genome expression arrays, 4 major hypotheses will be tested at different levels: (1) There may be interactive effects of copper and cyanobacterial stressors on life-history traits (e.g., reproduction) in Daphnia magna (individual level); (2) Combined effects of Cu and cyanobacterial toxicity on D. magna population dynamics under realistic time variable conditions can be predicted using process-based toxicity models, including under conditions of projected climate change (population-dynamics level); (3) Genetic adaptation of D. magna populations to Cu stress may alter their tolerance to cyanobacterial stressors (micro-evolutionary level); (4) Interactive effects between Cu and cyanobacterial stress occur due to interactions at uptake, toxification, detoxification, stress response or elimination pathways (physiological and genomic level). A chemical stress ecology approach will be followed throughout, as this will ultimately enable to incorporate climate change aspects into ecological risk assessment and environmental quality standards for copper.