Experimental evaluation of marine fogging as a coral bleaching intervention method

The management of corals over the next 50 years in the face of climate change will be crucial to the long-term survival of many coral reef ecosystems. Global emission reductions remain the primary strategy to sustain coral reefs; however, active intervention methods to protect corals from the impact of marine heatwaves are increasingly being considered as part of coral reef management plans. One method of coral bleaching mitigation involves aerosolising seawater, creating a fog layer that can reduce irradiance-driven stress. Here, the efficacy of seawater fogging for reducing coral bleaching stress was tested for the first time in an aquaria-based bleaching experiment using Pocillopora meandrina. The experiment had two orthogonal factors: (a) temperature (2 levels - heat-stressed and control, (b) fog (2 levels - 20 - 25% light reduction by fog for 6 h daily and non-fogged). A mean fog level of 21.5% improved symbiont density and lowered per cent whiteness but also decreased photosynthetic efficiency. Overall, fogging was effective in reducing irradiance; however, the mixed responses observed for Pocillopora meandrina highlight the need for further research on the effects of low and variable-shading techniques, such as fogging, for mitigating coral bleaching.