Figure 4.

Incorporating hypoxia stress into the coral bleaching response. ROS accumulation is commonly observed in heat stressed corals, although it is unclear whether it is the actual trigger or a ‘smoking gun’, i.e. downstream of further upstream events that initiate the symbiotic breakdown^22,97. Despite such uncertainties, hypoxia stress during heating may play a pivotal role in determining coral bleaching susceptibility. Specifically, hypoxia- and heat-driven excessive oxidative stress could hamper signalling of the Hypoxia-inducible Factor (HIF) hypoxia response system (HRS), enhance photodamage, and leave the coral immune-compromised. Increasing deoxygenation may thus increase coral bleaching susceptibility.