Exploration and study of the impact of climate change on microbial mats in the Nouvelle-Aquitaine region

• Main Author: Mazière, Camille
• Other Authors: Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS), LIttoral ENvironnement et Sociétés (LIENSs), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Université de Pau et des Pays de l'Adour, Université de La Rochelle, Christine Dupuy, Robert Duran
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2021
• Subjects: Microbial mats; Salterns; Climate change; Ocean acidification; Ocean warming; Tapis microbiens; Marais salants; Changement climatique; Acidification de l'océan; Réchauffement océanique; [SDV.BC]Life Sciences [q-bio]/Cellular Biology
• Online Access: https://theses.hal.science/tel-03551876; https://theses.hal.science/tel-03551876/document; https://theses.hal.science/tel-03551876/file/thesismaziere.pdf

The Intergovernmental Panel on Climate Change (IPCC, 2014) predicts that marine ecosystems will face many environmental pressures by 2100, in particular ocean acidification and warming. In coastal areas, microbial mats play key roles in the transformation of organic matter and the dynamics of biogeochemical cycles. The impacts of climate change on marine ecosystems have been widely studied at the global level but very little at the local level. They are particularly poorly understood in the Nouvelle-Aquitaine region (France). It is essential to understand the structural and functional modifications and dynamics of microbial communities in response to climate change. This thesis aims to define the impact of ocean warming and acidification on the microbial mats of Ré Island. First, a study of this microbial structure was perfomed in situ, in several types of salt marshes and according to the seasons, allowing to select the most suitable area to collect microbial mat and the season of sampling. The selected microbial mats were then maintained in mesocosms at laboratory. An increase in water temperature and a decrease in water pH were simulated for 8 weeks according to the most pessimistic predictions (RCP8.5) of the IPCC (2014) for 2100. Daily monitoring of physical-chemical parameters and weekly sampling of the microbial mat were performed to follow the functional dynamics and characterise the diversity changes. Acidification impacted the diversity and functioning of the microbial mats, particularly on the phototrophic communities. It has contributed to a decrease in prokaryotic diversity and an increase in some archaea that parasitise other archaea. The warming of the water had rather an effect on eukaryotic communities, with a change in Chlorophyceae and Diatomea abundance. The combination of these two conditions had less impact than the conditions alone suggesting a mitigating effect between them. However, in their current natural environment, these microbial mats already face temperatures higher or equal to ...