Reef accretion, coastal protection and reef functioning in the face of global change

• Main Author: Carlot, Jérémy
• Other Authors: Centre de recherches insulaires et observatoire de l'environnement (CRIOBE), Université de Perpignan Via Domitia (UPVD)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres, Valériano Parravicini
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2021
• Subjects: Reef accretion; Coastal protection; Reef functionning; Global change; Scleractinian corals; Sea-Level rise; Accrétion récifale; Protection côtière; Fonctionnement récifal; Changements globaux; Coraux scleractinaires; Montée des eaux; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Ice Sheet
• Online Access: https://theses.hal.science/tel-04324256; https://theses.hal.science/tel-04324256/document; https://theses.hal.science/tel-04324256/file/2021UPSLP094_archivage_pdf.pdf

In 1990, the Intergovernmental Panel on Climate Change (IPCC) highlighted that, from the last 100 years, the Earth has warmed between 0.3°C and 0.6°C due to an unprecedented increase in anthropogenic activity. This increase in global surface temperatures has acted as a snowball effect, reducing the ice sheet and thus increasing the global mean sea level (GMSL). More worryingly, the combined rise in temperature and sea level threatens many ecosystems, the most threatened of which would undoubtedly be coral reefs. Coral reefs are home to incredible biodiversity and provide shelter and food for over 500 million people worldwide. Although the reef barrier of many tropical islands protects coastal populations from ocean waves, their effectiveness is being reduced by global change. Coral cover is being reduced by various stresses such as the crown of thorns starfish outbreaks (Acanthaster cf. solaris), cyclones and bleaching events. The latter are becoming increasingly frequent and intense, acting on large scales. As a result, coral reefs are, in the worst case, depopulated or, in the best case, severely reduced, with far fewer three-dimensionally complex individuals (i.e., those with the greatest potential to reduce wave energy) than before, threatening the future of coastal populations. In this Ph.D., I quantify the impact of climate change on coral reefs in Mo'orea (French Polynesia). I define 1) how the topography (also called structural complexity) evolves and 2) the potential accretion rate of coral reefs between 2005 and 2016. I also investigate coral demographic dynamics to better predict future coral assemblages. My results show that average structural complexity in Mo'orea recovered to pre-disturbance levels by 2016. These observations are encouraging since during extreme events (such as cyclones), and in the absence of high structural complexity, the energy of waves hitting the coast is significantly higher than previously estimated. Unfortunately, I also demonstrate that accretion rates remain below the ...