A photophysiological model of coral bleaching simulates declines and recovery during an emulated multi-doldrum marine heatwave event

Abstract

Mass coral bleaching events have become increasingly frequent since the 1980s as sea surface temperatures have risen. Extremes of light and temperature stress leading to coral bleaching can develop when doldrum meteorological conditions occur during a marine heatwave event. The coral bleaching model simulates bleaching by tracking the build-up of reactive oxygen species driven by temperature-mediated, light-driven oxidative stress, triggering symbiont cell expulsion. This study is the first to evaluate the coral bleaching model for its ability to simulate heat and light stress dynamics in the coral Acropora kenti over multiple doldrum events and an intermediate recovery period. We tested model fidelity by comparing model predictions against laboratory measurements of coral bleaching stress taken during an emulated multi-doldrum marine heatwave event, incorporating artificial shade treatments. The model consistently predicted greater bleaching at increased temperatures and reduced shade levels, with an intermediate recovery period simulated between the doldrum events. Simulated bleaching stress captured up to fifty per cent of the variation in observed antioxidant enzyme activity. This study confirms that the significant emergent features of the model are present, as overall, the model adequately represented bleaching outcomes concerning the interactions between temperature and light. Thus, process-based modelling could be a valuable tool for predicting bleaching outcomes and optimising shading techniques, providing scientific managers with actionable strategies for mitigating coral bleaching.