Post-Heatwave Coral Health Coincides With Host-Specific Symbiodiniaceae-Bacteria Consortia

Coral reefs are facing unprecedented damage due to climate-driven marine heatwaves (MHWs). While coral response to elevated temperatures is inextricably linked to coral-associated microalgae (Symbiodiniaceae) and bacteria, the role of algal-bacterial interactions in affecting coral resilience to thermal stress remains obscure. Here we show coral health indicated by distinct compositions of Symbiodiniaceae-bacteria consortia in two coral species, the massive Porites lutea and the laminar Duncanopsammia peltata, upon exposure to an unusual MHW. P. lutea exhibited thermal resilience by maintaining an obligate partnership with the heat-tolerant Cladocopium C15 under both healthy and bleached states, alongside conservative bacterial community changes between the two states driven primarily by deterministic processes; whereas D. peltata associated with the heat-sensitive Cladocopium C1 in bleached state but the heat-tolerant Durusdinium D1/D4 in healthy state, with stochastically driven, more liberal bacterial community changes between the two states. This distinction between P. lutea and D. peltata in their Symbiodiniaceae-bacteria consortia reflects a specialist/generalist strategy in partner selection given the status of coral health, underscoring an evolutionary trade-off between high-fidelity symbioses for persistence under chronic stress and rapid microbiome turnover for transient bleaching resilience. Broadly, the host-specific, coordinated Symbiodiniaceae-bacteria community differentiation following MHWs, may inform future coral conservation and restoration practises in an era of escalating climate change.