Ocean acidification (OA) and high light was found to negatively affect the Antarctic key species Phaeocystis antarctica, Fragilariopsis kerguelensis and Chaetoceros debilis. To unravel the underlying physiological response at the transcriptomic level, these species were grown under ambient and elevated pCO 2 combined with low or high light. RNA sequencing revealed that the haptophyte was much more tolerant towards OA than the two diatoms as only these showed distinct OA-dependent gene regulation patterns. Under ambient pCO 2 , high light resulted in decreased glycolysis in P. antarctica. Contrastingly, upregulation of genes related to cell division and transcription as well as reduced expression of both cata- and anabolic carbon related pathways were seen in C. debilis. OA in combination with low light led to reduced respiration, but also surprisingly to higher expression of genes involved in light protection, transcription and translation in C. debilis. Though not affecting P. antarctica, OA combined with high light caused also photosensitivity in both diatoms. As additional response reallocation of carbon to lipids was found in C. debilis under these conditions. Overall, we conclude that P. antarctica is better adapted than the two diatoms to OA and high light.