Differing proteome responses to ocean acidification between two common pocilloporid corals

Abstract Ocean acidification threatens coral reef ecosystems by challenging calcification processes fundamental to reef accretion. Yet many corals continue to calcify under elevated p CO 2 , suggesting species-specific physiological plasticity and potential cellular compensations. Here, we use label-free quantitative proteomics to investigate proteomic responses of two common pocilloporid corals, Stylophora pistillata and Pocillopora damicornis , with known differential resistance to ocean acidification after two months at moderate (~ 940 ppm) and high (~ 2,800 ppm) p CO 2 compared to the control (~ 480 ppm). S. pistillata exhibited extensive proteomic restructuring under high p CO 2 , marked by widespread declines of energy-generating pathways, yet selective increase of proteins involved in ion transport, cytoskeletal stability, and stress responses. This indicates a strategy of general metabolic suppression coupled with targeted investment into essential cellular functions, potentially sustaining calcification despite reduced overall metabolic capacity. In contrast, P. damicornis showed much less proteomic adjustment, primarily involving structural proteins and those potentially linked to cellular redox balance, signifying a moderate, targeted strategy for physiological stability. These divergent responses highlight contrasting modes of resistance (plasticity versus stability). Integrated with physiological data, our findings clarify cellular mechanisms controlling calcification, demonstrating the value of proteomics in coral ecophysiology and providing new insights into species-specific vulnerability under future ocean conditions.