The current exposure of species assemblages to high environmental variability may grant them resilience to future increases in climatic variability. In globally threatened coral reef ecosystems, management seeks to protect resilient reefs within variable environments. Yet, our lack of understanding for the determinants of coral population performance within variable environments hinders forecasting the future reassembly of coral communities. Here, using Integral Projection Models, we compare the short- (i.e., transient) and long-term (i.e., asymptotic) demographic characteristics of tropical and subtropical coral assemblages to evaluate how thermal variability influences the structural composition of coral communities over time. Exploring spatial variation across the dynamics of functionally different competitive, stress-tolerant, and weedy coral assemblages in Australia and Japan, we show that coral assemblages trade-off long-term performance for transient potential in response to thermal variability. We illustrate how coral assemblages can reduce their susceptibility towards environmental variation by exploiting volatile short-term demographic strategies, thus enhancing their persistence within variable environments. However, we also reveal considerable variation across the vulnerability of competitive, stress-tolerant, and weedy coral assemblages towards future increases in thermal variability. In particular, stress-tolerant and weedy corals possess an enhanced capacity for elevating their transient potential in response to environmental variability. Accordingly, despite their current exposure to high thermal variability, future climatic shifts threaten the structural complexity of coral assemblages, derived mostly from competitive coral taxa within highly variable subtropical environments, emulating the degradation expected across global coral communities.