Unveiling the role of Rhizaria in the silicon cycle

• Main Author: Llopis Monferrer, Natalia
• Other Authors: Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Paul Tréguer, Aude Leynaert, Fabrice Not
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2020
• Subjects: Silicon cycle; Biogenic silica; Silicic acid uptake; Rhizaria; Polycystina; Phaeodaria; Cycle de la silice; Silice biogénique; Production de silice; Polycystines; [CHIM.OTHE]Chemical Sciences/Other; Ross Sea
• Online Access: https://tel.archives-ouvertes.fr/tel-03259625; https://tel.archives-ouvertes.fr/tel-03259625/document; https://tel.archives-ouvertes.fr/tel-03259625/file/These-2020-SML-Chimie_marine-LLOPIS_MONFERRER_Natalia.pdf

Rhizaria are ubiquitous planktonic protists, thriving from surface waters to bathypelagicecosystems. A number of rhizarians taxa (i.e., polycystines, phaeodarians) build complex and robust siliceous skeletons. Yet, basic knowledge such as abundances, diversity, cellular content (biogenic silica-bSi, carbon and nitrogen) and silicon (Si) uptake rates of rhizarians are poorly known. This lack of knowledge prevents an accurate estimate of their contribution to the Si biogeochemical cycle. To address this issue, Si uptake rates —using the 32Siradioisotope— and cellular content were measured during three research cruises (Mediterranean Sea, Ross Sea and Atlantic Ocean). High individual production rates (up to 9 nmol-Si cell-1d-1) and Si content (up to 11.9 nmol-Si cell-1) were reported, as compared to diatoms. Combining these first results with previously published abundance data, the contribution of these organisms to the biogeochemical cycling of Si was assessed,revealing that Rhizaria contribute up to 22% of the bSi production in the global ocean. Additionally, the abundance, biomass and diversity of Rhizaria were quantified by pairing imaging tools (FlowCAM, Zooscan and UVP) and molecular barcode techniques to cover the wide size range represented by Rhizaria in the NW Mediterranean Sea. This integrative approach revealed that Rhizaria represent up to 6% of the bSi in the first 500 metres of the water column. Overall, this work provides unique quantitative data that highlight the impact of rhizarians in the cycling of Si in the ocean. This thesis work also emphasizes the need toexplore further the deep ocean to refine our first estimates of Rhizarian contribution to the Sibiogeochemical cycle at local and global scales Les Rhizaria sont des protistes planctoniques présents à la surface et dans l’ensemble des océans. Certains taxons (i.e., polycystines, Phaeodaria) construisent des squelettes siliceux complexes et robustes. Les connaissances de base telles que l'abondance, la diversité, le contenu cellulaire ...