Composition of diatom communities and their contribution to plankton biomass in the naturally iron-fertilized region of Kerguelen in the Southern Ocean

• Published in: FEMS Microbiology Ecology
• Main Authors: Lasbleiz, Marine, Leblanc, Karine, Armand, Leanne, Christaki, Urania, Georges, Clément, Obernosterer, Ingrid, Queguiner, Bernard
• Other Authors: Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Department of Biological Sciences North Ryde, Macquarie University, 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 ), Laboratoire d'Océanographie Microbienne (LOMIC), Institut national des sciences de l'Univers (INSU - CNRS)-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)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: natural iron fertilization; Southern Ocean; plankton community structure; diatoms; carbon biomass; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDV.BID.SPT]Life Sciences [q-bio]/Biodiversity/Systematics; Phylogenetics and taxonomy; [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; Kerguelen; Kerguelen Islands
• Online Access: https://hal.science/hal-01664911; https://hal.science/hal-01664911/document; https://hal.science/hal-01664911/file/Lasbleiz,2016-HAL.pdf; https://doi.org/10.1093/femsec/fiw171

International audience One sentence summary: The phenology of the naturally iron-induced phytoplankton blooms east of the Kerguelen Islands was investigated by documenting the spatial and temporal variation of phytoplankton community structure concurrently with biogeochemical observations. ABSTRACT In the naturally iron-fertilized surface waters of the northern Kerguelen Plateau region, the early spring diatom community composition and contribution to plankton carbon biomass were investigated and compared with the high nutrient, low chlorophyll (HNLC) surrounding waters. The large iron-induced blooms were dominated by small diatom species belonging to the genera Chaetoceros (Hyalochaete) and Thalassiosira, which rapidly responded to the onset of favorable light-conditions in the meander of the Polar Front. In comparison, the iron-limited HNLC area was typically characterized by autotrophic nanoeukaryote-dominated communities and by larger and more heavily silicified diatom species (e.g. Fragilariopsis spp.). Our results support the hypothesis that diatoms are valuable vectors of carbon export to depth in naturally iron-fertilized systems of the Southern Ocean. Furthermore, our results corroborate observations of the exported diatom assemblage from a sediment trap deployed in the iron-fertilized area, whereby the dominant Chaetoceros (Hyalochaete) cells were less efficiently exported than the less abundant, yet heavily silicified, cells of Thalassionema nitzschioides and Fragilariopsis kerguelensis. Our observations emphasize the strong influence of species-specific diatom cell properties combined with trophic interactions on matter export efficiency, and illustrate the tight link between the specific composition of phytoplankton communities and the biogeochemical properties characterizing the study area.