A macroecological perspective of interactions between local conditions and global warming on coral reefs

  • Jack V. Johnson

Student thesis: Doctoral ThesisDoctor of Philosophy


Coral reefs are the most biodiverse habitats in the ocean, performing critical roles for marine ecosystem function and for the subsistence of large human societies that rely on the resources they provide. With the accumulating effects of global industrialization, and the resulting anthropogenic warming of marine ecosystems, coral reefs are undergoing alarming rates of decline, caused primarily by global warming induced coral bleaching (the expulsion of photosynthetic endosymbionts). In addition to global warming, the local-scale impacts of other stressors related to anthropogenic development of coastal regions can also cause coral reef declines. Thus, a widespread assumption that local stressors synergistically interact with global warming to exacerbate bleaching and reef degradation exists. Given the vital role of coral reefs for human society combined with their continued declines, understanding coral stability and drivers of bleaching at a global scale is one of the key challenges in modern biology, and relates to a wide spectrum of the UN Sustainable Development Goals. In response to this growing challenge, I implemented a global-scale research programme aimed to assess the relationship between global warming with local conditions for driving reef declines. Firstly, I showed that Marine Protected Areas (MPAs) do not buffer corals from bleaching during marine heatwaves, suggesting continued reef decline under global warming regardless of protected status. Secondly, my analyses revealed that local human population density does not exacerbate coral bleaching under global warming, dispelling the long held view that reefs isolated from human populations are refuge under climate change. Thirdly, multi-stressor environments of mangroves actually reduce bleaching during heat stress, with the most profound reductions shown at the highest levels of warming for reef corals closest to mangroves. Lastly, I examined a case study in the Indo-Pacific and Caribbean, showing local scale variance in response of benthic components to heat stress. Overall, the original evidence gathered from my PhD shows that local conditions do not synergistically interact with warming to induce coral bleaching and coral decline. Rather, corals which reside in unprotected waters, and in the presence of local stressors, are most likely co-tolerant species that can withstand the impacts of cumulative stressors.

Additionally, global warming may even eclipse the effect of local stressors, highlighting that continued anthropogenic heating threatens all coral reefs regardless of local conditions. Therefore, for coral reefs to survive the Anthropocene, it is critical to tackle the direct cause of anthropogenic global warming by reducing the consumption of fossil fuels responsible for greenhouse gas emissions. My PhD offers four original research articles published in leading journals that reinforce this message.

Date of AwardDec 2023
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorDaniel Pincheira-Donoso (Supervisor) & Jaimie Thomas Allan Dick (Supervisor)


  • Macroecology
  • coral reefs
  • multiple stressors
  • synergistic
  • antagonistic

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