Environmental drivers such as temperature and CO2 have in effect on early live stages. This overview will show different sensitivities of eggs and early larvae of crustaceans and fish. We measured mortality, developmental time, oxygen consumption and heart beat to get a comprehensive overview about the performance of these life stages and effects on later stages. Our experiments show synergistic effects of ocean warming and acidification on eggs and hatching larvae of crustaceans and fish. Interestingly, crab larvae hatching from eggs that were incubated at high CO2 showed higher mortality and prolonged developmental time compared to eggs that were kept at ambient CO2. Embryonic survival (p = 0.015) and larval size at hatch (p < 0,01) were significantly reduced under high PCO2, especially towards unfavourably cold temperatures. In turn, respiration rates of developing embryos were significantly (p < 0.05) increased under high PCO2, suggesting higher energy demand due to e.g. increased acid-base regulation leaving less energy for larval growth. These experiments suggest that life history stages and transition phases with lowered physiological capacities will be most sensitive to ocean warming and acidification.