• Marcelle Barreto

Student thesis: Doctoral Thesis


The rise of atmospheric CO2 is a threat to many ecosystems, including coral reefs. Rising sea surface temperatures are known to interfere on coral health and cause extensive worldwide mortality. In the Red Sea, coral reefs are spread across 18 degrees of latitude, resulting in a temperature gradient with maximum monthly mean sea surface temperatures ranging from around 33 °C in the south to 27°C in the north. Such gradients can lead to adaptations to local conditions, with coral thermal performance expected to increase along temperature/latitude gradients. In this research, I used the corals Porites lobata and Platygyra daedalea collected in various locations in the Red Sea to resolve fine-scale populational differences in thermotolerance along the Red Sea, and assess if this variability can be explored for potential assisted gene flow projects (i.e. assisted migration and selective breeding) within the Red Sea region. In chapter two, a heat stress assay indicated that P. lobata colonies from the Southern Red Sea have a higher thermal bleaching threshold than conspecifics from Northern latitudes, highlighting their potential as source of temperature resilient colonies. In chapter three, a common garden experimental design showed that thermotolerance of southern P. lobata colonies is maintained when transplanted to a foreign environment. However, despite lack of bleaching in Southern colonies, mortality rates of approximately 20% suggested that other environmental constraints besides temperature might impact coral health and survival. In chapter four, purebred Arabian Gulf larvae generated by cross-breeding colonies of Platygyra daedalea collected along the Red Sea and the Arabian Gulf showed higher survival under heat stress. In addition, paternal survival index increased in crosses with fathers from warmer locations. These results combined indicate that assisted gene flow via translocation alone may have limited success due to a lack of local adaptations to environmental conditions other than temperature. Nonetheless, inter-populational breeding may overcome these limitations as they could generate offspring with both increased thermal tolerance and local adaptations.
Date of AwardDec 2022
Original languageEnglish (US)
Awarding Institution
  • Biological, Environmental Sciences and Engineering
SupervisorManuel Aranda (Supervisor)


  • Coral
  • thermotolerance
  • assisted evolution
  • assisted gene flow
  • selective breeding
  • assisted migration

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