Differing proteome responses to ocean acidification between two common pocilloporid corals

Ocean acidification increasingly threatens coral reef ecosystems by challenging calcifi-cation processes fundamental to reef accretion. Yet, many corals continue to calcify under elevated pCO₂, suggesting species-specific physiological plasticity and potential cellular compensations. Here, we investigate the proteomic responses of two common pocilloporid corals, Stylophora pistillata and Pocillopora damicornis, to moderate (~940 ppm) and high (~2,800 ppm) pCO₂ over a two-month period. Using label-free quantita-tive proteomics, we identify changes in protein abundances compared to control con-ditions (~480 ppm) and infer functional shifts that underlie their respective responses to acidification. S. pistillata exhibited extensive proteomic restructuring under high pCO₂, marked by downregulation of metabolic pathways and concurrent upregulation of ion transporters, cytoskeletal elements, and stress response proteins, suggesting a meta-bolically costly but flexible strategy to sustain calcification. In contrast, P. damicornis showed fewer and more moderate proteomic changes, with adjustments in structural proteins and redox regulation, indicating a more restrained acclimatization strategy. These divergent responses highlight contrasting modes of resistance (plasticity versus stability). In direct context to physiological and geochemical data, our findings reveal cellular mechanisms of calcification control and underscore the utility of proteomics in coral ecophysiology, offering new insights into species-specific vulnerability and po-tential adaptive capacities under future ocean conditions.