Modelling as a tool for predicting coral reef futures

The mechanistic bleaching model was refined to represent Acropora divaricata (more commonly known as Branching Coral) and successfully predicted the onset of bleaching under increased temperature and elevated light. The model’s output aligned closely with the initial decline in photosynthetic performance observed in lab experiments designed to represent conditions corals might encounter during a bleaching event on the Great Barrier Reef.

“A validated model is crucial for assessing reef interventions and management strategies and giving insights into how reefs might fare under various climate scenarios,” said lead author Sophia Ellis, PhD candidate at Southern Cross University.

“These findings highlight the value of modelling for predicting bleaching under multiple environmental stressors.”

The updated coral bleaching model now supports the Reef Restoration and Adaptation Program’s (RRAP) research on optimising shading interventions to protect the Great Barrier Reef.

"This research is important because it uses laboratory experiments to quantify the skill of the coral bleaching model that we use in eReefs. In particular, the paper shows that the model captures the timing of bleaching onset to thermal stress events,” said co-author Dr Mark Baird, CSIRO Research Director of Coastal and Oceanic Systems.

Coral bleaching is a major threat to reefs worldwide, especially during marine heatwave events, which are increasing in frequency and intensity with climate change. Researchers are investigating interventions to protect corals from bleaching stress on the Great Barrier Reef.

One innovative approach investigated by the RRAP Cooling and Shading R&D subprogram – marine cloud brightening – aims to reduce the amount of solar radiation reaching the Reef, effectively cooling and shading corals during marine heatwave events.

“Shading technologies could relieve bleaching stress over large portions of the Reef,” said Cooling and Shading subprogram lead and principal supervisor of the PhD research, Associate Professor Daniel Harrison of Southern Cross University.

“Numerical modelling is crucial for extrapolating performance estimates and informing the target shade level and duration.”

Models can help us understand how corals respond to heat and light stress during bleaching events. The coral bleaching model is nestled within the eReefs marine biogeochemical model. eReefs is a comprehensive operational information system for managing the Great Barrier Reef ecosystem.

The eReefs research project is a collaboration between Australia’s national science agency CSIRO, the Australian Institute of Marine Science and the Queensland Government, funded by the Australian Government Department of Climate Change, Energy, the Environment and Water.

“Next, we’ll test the revised configuration of the coral bleaching model for predicting bleaching outcomes in an emulated multi-doldrum marine heatwave event, incorporating artificial shade treatments,” said Sophia.

This work was funded by the Reef Restoration and Adaptation Program, a partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.

Study details

"A photophysiological model of coral bleaching under light and temperature stress: experimental assessment" by Sophia Ellis, Mark Baird, Luke Harrison, Kai Schulz, Daniel Harrison.

Published in Conservation Physiology

DOI:  https://doi.org/10.1093/conphys/coaf020