Effect of the temperature on cold-water coral holobiont in the North-East Atlantic Ocean

• Main Author: Chemel, Mathilde
• Other Authors: Laboratoire d'Ecogéochimie des environnements benthiques (LECOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Observatoire océanologique de Banyuls (OOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Franck Lartaud, Pierre E. Galand
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2023
• Subjects: Cold-water corals; Climatic changes; Lophelia pertusa; Madrepora oculata; Microbiome; Coraux d'eau froide; Changements climatiques; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; North East Atlantic
• Online Access: https://theses.hal.science/tel-04506647; https://theses.hal.science/tel-04506647/document; https://theses.hal.science/tel-04506647/file/141860_CHEMEL_2023_archivage.pdf

Cold-water corals such as Lophelia pertusa and Madrepora oculata, two key reef-forming species distributed worldwide, form extensive reefs providing highly valuable habitats for diverse biological communities. They are particularly threatened by increasing temperature, as models predict that temperature would further increase by up to 3 °C in the Atlantic Ocean before the end of the century. Recent work has characterised the cold-water coral ecology and has shown degraded health status both in response to lower and increased temperatures in different scleractinian species. However, the underlying molecular mechanisms of their thermal response, including the response at the holobiont level (i.e. the coral host and its associated microbiome), is still poorly known. Understanding the response of cold-water corals to ocean warming using integrative approach is of paramount importance to evaluate their resilience to future water temperatures. The goal of this thesis was firstly to describe the in situ dynamics of the holobiont from L. pertusa and M. oculata in a canyon of the Bay of Biscay (NE Atlantic Ocean) to determine potential differences between Atlantic and Mediterranean populations at the growth and microbiome levels. The average polyp linear growth measured for L. pertusa was 2.4 ± 1.6 mm yr−1, which fall in the lower range compared to previous estimations. Mortality and breakage were total in M. oculata could not allow characterization of growth. Concurrently, the microbial community determination showed that L. pertusa microbiome was versatile between the two regions with high variability within canyons, while M. oculata exhibited stable microbiome across the different regions, with strong association with some bacteria. Secondly, the reproductive biology of those two species in the Mediterranean Sea was also investigated to determine potential seasonal differences with the Atlantic population. The gametogenic cycle suggests a seasonal spawning of L. pertusa in autumn to early winter, corresponding to the ...