The responses in size, survival and other life-history traits in the cladoceran Daphnia magna were assessed at two temperatures (15 and 25ºC) across a calcium (Ca) gradient (0.5, 4 and 106 mg Ca/l) for two different clones from Sweden and Morocco. Individuals reared at 0.5 mg Ca/l suffered a strong detrimental impact on their overall body size, survival, moulting, age at maturity and reproduction. Temperature, individual- and interactively with Ca limitation, affected all measured traits, and in particular growth rate. Both clones responded differently to both Ca and temperature effects as well. In addition, our results of reduced performance for the highest Ca level hinted a “knife-edge” effect for most variables to Ca availability. These results of the interaction between temperature and Ca limitation suggest future consequences for freshwater zooplankton and communities, as temperature rises with global warming and Ca continues to decline in boreal ecosystems.