Differential susceptibility of reef-building corals to deoxygenation reveals remarkable hypoxia tolerance

Ocean deoxygenation threatens the persistence of coastal ecosystems worldwide. Despite an increasing awareness that coastal deoxygenation impacts tropical habitats, there remains a paucity of empirical data on the effects of oxygen limitation on reef-building corals. To address this knowledge gap, we conducted laboratory experiments with ecologically important Caribbean corals Acropora cervicornis and Orbicella faveolata. We tested the effects of continuous exposure to conditions ranging from extreme deoxygenation to normoxia (similar to 1.0 to 6.25 mg L-1 dissolved oxygen) on coral bleaching, photophysiology, and survival. Coral species demonstrated markedly different temporal resistance to deoxygenation, and within a species there were minimal genotype-specific treatment effects. Acropora cervicornis suffered tissue loss and mortality within a day of exposure to severe deoxygenation (similar to 1.0 mg L-1), whereas O. faveolata remained unaffected after 11 days of continuous exposure to 1.0 mg L-1. Intermediate deoxygenation treatments (similar to 2.25 mg L-1, similar to 4.25 mg L-1) elicited minimal responses in both species, indicating a low oxygen threshold for coral mortality and coral resilience to oxygen concentrations that are lethal for other marine organisms. These findings demonstrate the potential for variability in species-specific hypoxia thresholds, which has important implications for our ability to predict how coral reefs may be affected as ocean deoxygenation intensifies. With deoxygenation emerging as a critical threat to tropical habitats, there is an urgent need to incorporate deoxygenation into coral reef research, management, and action plans to facilitate better stewardship of coral reefs in an era of rapid environmental change.

Automated summary

The study highlights the variability in species-specific hypoxia thresholds and the importance of incorporating deoxygenation into coral reef research and management plans. Different coral species showed distinct responses to deoxygenation, shedding light on their resilience and mortality thresholds under low oxygen conditions. This has significant implications for predicting the impact of ocean deoxygenation on coral reefs in the future.