Biodiversity of testate amoebae and environments of Kerguelen archipelago : current characterization and recent evolution under climatic constraints

• Main Author: Herlédan, Maïwenn
• Other Authors: Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187 (LOG), Institut national des sciences de l'Univers (INSU - CNRS)-Université du Littoral Côte d'Opale (ULCO)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD France-Nord ), Université de Lille, Éric Armynot du Châtelet, Viviane Bout-Roumazeilles
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Climate change; Testate amoebae; Kerguelen; Subantarctic islands; Biodiversity; Paleoenvironment; Amibes à thèques; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarctic; Antarc*
• Online Access: https://theses.hal.science/tel-04221914; https://theses.hal.science/tel-04221914/document; https://theses.hal.science/tel-04221914/file/These_HERLEDAN_Maiwenn.pdf

The objective of this PhD is to describe the current diversity of testate amoebae on the Kerguelen archipelago depending on climate and environmental context and to understand the recent evolution of the last 260 years by a paleoenvironmental approach combining microscopic observations, sedimentology and geochemistry. Located at the polar front in the sub-Antarctic zone, the Kerguelen archipelago is subject to extreme wind and precipitation conditions while being preserved from direct anthropic impacts. This makes it an ideal natural environment to study the impact of global climate change on the environment.Two scientific campaigns on the Kerguelen archipelago in 2019 and 2021 have allowed us to collect samples of current plants (mainly bryophytes and azorelles), underlying soils and soil cores. The samples studied were selected to reflect the geographical and geological diversity of the archipelago, in terms of rainfall (west-east contrast), sedimentary nature (organic soil, alluvial sediments, etc. ) and petrographic context (basalts - phonolites). Optical observations of the testate amoebae communities growing in the plant samples (101 samples) have allowed us to build a new database of testate amoebae in the archipelago. Sedimentological and geochemical analyses (water content, elemental and isotopic analyses, mineralogy) were carried out in parallel on 485 soil samples in order to characterize the environmental parameters.This work has allowed to update and complete the 1981 database of 50 species with the description of 107 species of testate amoebae. Sedimentological analyses of soils revealed significant differences in terms of weathering between the western and eastern parts of the archipelago, reflecting contrasting rainfall patterns. This trend is also reflected in the testate amoebae assemblages whose diversity, variable according to the type of environment, is much greater in the west. The coupling of these different observations has made it possible to highlight the ecological affinities of ...