Decadal tracking reveals species-specific limits to coral thermal acclimatization

Abstract

Mass coral bleaching events driven by marine heatwaves are increasing in frequency and severity, yet the long-term recovery trajectories of surviving corals remain poorly understood. Here, leveraging a cohort of individual coral colonies with a decade of tracked environmental and bleaching history, we captured structural shifts in the coral thermal performance landscape. Specifically, we quantified thermal performance curves (TPCs) for photosynthesis and calcification in bleaching-resistant and bleaching-susceptible colonies of two ecologically dominant reef-building corals (Montipora capitata and Porites compressa) at four and six years following the 2019 marine heatwave in K[a]neohe Bay, Hawaii (2023 and 2025, respectively). Coral thermal performance shifted substantially between 2023 and 2025, and these shifts differed between species, bleaching phenotypes, and traits. In P. compressa, photosynthetic thermal optimum (Topt) shifted downward over time by 1.6{degrees}C across both phenotypes, suggesting recalibration toward prevailing conditions at the potential cost of future heat tolerance. In M. capitata, photosynthetic performance was lower in bleaching-susceptible corals in 2023 but converged by 2025, suggesting susceptible colonies recovered. In contrast, Topt of photosynthesis remained persistently higher in bleaching-resistant colonies, likely reflecting established symbiont communities. Critically, photosynthesis and calcification did not recover in parallel. Calcification TPCs for both phenotypes of M. capitata were stable across both timepoints, whereas calcification TPCs in P. compressa continued to change through 2025. These findings demonstrate that coral thermal performance is not static following heatwaves but continues to be reshaped over multi-year recovery periods, and that species-specific traits and strategies can fundamentally constrain the pace and coupling of physiological recovery. Furthermore, elevated thermal tolerance acquired through a heatwave can erode during prolonged periods of ambient temperatures. As recurrent bleaching events shorten recovery windows, understanding these dynamic physiological trajectories are essential for understanding and forecasting reef futures.