Thesis
The role of light and temperature in coral bleaching: exploring the physiological response (Citation and Abstract only)
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2025
DOI:
https://doi.org/10.25918/thesis.530
Appears in Recent Southern Cross PhD Theses
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Abstract
Around the world, marine heatwave events continue to trigger mass coral bleaching and mortality from rising ocean temperatures. While light and temperature are key stressors, their combined effects on coral health, especially across multiple doldrum events and with shading interventions, remain poorly understood. Numerical modelling, underpinned by experimental evidence, provides a valuable tool for exploring these interactions and assessing the role of environmental stressors in future bleaching events. Few numerical physiological models integrate both light and temperature to simulate coral bleaching.
A topical review summarised coral physiological modelling frameworks under the impacts of various drivers (Chapter 2). Temperature and light were indicated as dominant independent variables, driving bleaching predictions. Furthermore, the coral bleaching response to light and temperature was experimentally assessed in two species of Acropora (Chapter 3). Shading significantly reduced the bleaching response in A. divaricata, whilst for some bleaching parameters, A. kenti responded negatively to shade. These findings underscored the nuanced role of shade in reducing bleaching under heat stress and highlighted the need to consider species-specific responses.
This thesis includes the first experimental validation of a temperature-mediated, light-driven model of coral bleaching from the perspective of the symbiont (Chapter 4). Measurements of coral health from bleaching experiments were used to guide the development of this numerical physiological model. The model was configured to simulate bleaching outcomes under experimental conditions with manipulated light and temperature levels. The model-simulated onset of physiological bleaching at heat stress and high light intensity closely corresponded (within a few days) with an initial observed photochemical decline in the experiment. This validation prompted further testing of the model across various environmental scenarios.
The model’s versatility was assessed through its ability to simulate heat and light stress dynamics in the coral A. kenti, over multiple doldrum events and an intermediate recovery period (Chapter 5). The model successfully represented bleaching outcomes during this complex experiment, including periods of stress and recovery under heat and light stress. Antioxidant enzyme activity captured up to fifty per cent of the variation in simulated bleaching stress, confirming key emergent features of the model.
Overall, findings indicate that moderate shading alleviates coral bleaching stress, though its effects varied among coral species and measured response variables. This research underscores the importance of considering species-specific responses to reduced light levels in bleaching interventions. It also demonstrates the value of process-based mechanistic modelling systems for simulating bleaching outcomes under multiple stressors. Assessing model fit through comparison with laboratory experiments can validate the model’s accuracy in representing the photophysiological processes within the coral-symbiont relationship. This approach will enhance the assessment of reef interventions and improve predictions of coral bleaching under various climate scenarios. Coral physiological modelling has significant potential applications, and this thesis could serve as a foundation for its continued development.
Details
- Title
- The role of light and temperature in coral bleaching: exploring the physiological response (Citation and Abstract only)
- Creators
- Sophia L. Ellis
- Contributors
- Daniel Patrick Harrison (Supervisor) - Southern Cross UniversityKai G Schulz (Supervisor) - Southern Cross UniversityMark E Baird (Supervisor) - CSIRO Oceans and Atmosphere
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Identifiers
- 991013328628602368
- Copyright
- © Sophia L. Ellis 2025
- Academic Unit
- Faculty of Science and Engineering; National Marine Science Centre
- Resource Type
- Thesis