Evaluating the role of coral trophic strategies in driving community shifts in response to heat stress via stable isotopes-based modeling

Corals are increasingly threatened by global climate change, which may lead to shifts in their community on geographic scales. Reef-building corals are mixotrophic and may increase heterotrophy to bolster their resilience to environmental stress. However, many studies only focus on trophic strategies at the species or genus level, overlooking whether the change in these strategies may cause community shifts. Prior to potential summer thermal events, we collected coral samples and classified them into different groups based on the shortest distance from the inner edge of the corallite wall (SDI), life history strategy (competitive vs. non-competitive), and evolutionary trajectory (complex vs. robust). Physiological measurements showed that the corals with small polyps, a competitive life history strategy, and membership in the complex clade had higher symbiotic density and greater chlorophyll content, indicating enhanced photosynthetic capacity. By integrating stable isotope analysis (δ13C and δ15N), Bayesian mixing models, and a kernel utilization density niche approach, we found that during summer, corals with larger SDI, non-competitive life history strategies, and robust evolutionary trajectory relied more on heterotrophy, a pattern suggesting greater resilience to thermal stress. These results are consistent with field observations, where coral groups with greater reliance on heterotrophy maintained their relative abundance after a local bleaching event. Our findings suggest that trophic strategies, inferred from summer states, may play a role in coral resilience and provide new insights into how coral reefs may respond to climate change.