Symbioses are restructured by repeated mass coral bleaching

Area of Science:

• Marine Biology
• Ecology
• Climate Change Science

Background:

• Coral reef survival under global warming necessitates rapid acclimation or adaptation.
• Mass coral bleaching events, like the one in 2016, significantly impact coral-algal symbioses.

Purpose of the Study:

• To compare the impact of accumulated heat stress on symbiont communities before and after the 2016 mass bleaching.
• To investigate symbiont community dynamics in three coral species and the surrounding environment across the Great Barrier Reef.

Main Methods:

• Analysis of 1643 symbiont communities from three coral species and free-living samples.
• Comparison of symbiont composition in samples collected before and after the 2016 mass bleaching event.
• Assessment of reef resilience based on aerial bleaching severity relative to satellite sea temperatures.

Main Results:

• Resilient reefs exhibited low symbiont variation.
• Before bleaching, heat-tolerant symbionts were abundant in the environment but scarce in corals.
• Post-bleaching, environmental symbiont diversity doubled, and coral symbiont communities showed dynamic or conserved restructuring depending on the species.

Conclusions:

• Symbiotic restructuring occurs after coral bleaching, representing a taxon-specific ecological opportunity.
• The ability of corals to host heat-tolerant symbionts is crucial for reef survival in a warming climate.