|Composition of diatom communities and theircontribution to plankton biomass in the naturallyiron-fertilized region of Kerguelen in the SouthernOcean |
(Article) Publié: Fems Microbiology Ecology, vol. p.Oxfordjournals (2016)
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In the naturally iron-fertilized surface waters of the northern Kerguelen Plateau region, the early spring diatom communitycomposition and contribution to plankton carbon biomass were investigated and compared with the high nutrient, lowchlorophyll (HNLC) surrounding waters. The large iron-induced blooms were dominated by small diatom species belongingto the genera Chaetoceros (Hyalochaete) and Thalassiosira, which rapidly responded to the onset of favorable light-conditionsin the meander of the Polar Front. In comparison, the iron-limited HNLC area was typically characterized by autotrophicnanoeukaryote-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-fertilizedsystems of the Southern Ocean. Furthermore, our results corroborate observations of the exported diatom assemblagefrom a sediment trap deployed in the iron-fertilized area, whereby the dominant Chaetoceros (Hyalochaete) cells were lessefficiently exported than the less abundant, yet heavily silicified, cells of Thalassionema nitzschioides and Fragilariopsiskerguelensis. Our observations emphasize the strong influence of species-specific diatom cell properties combined withtrophic interactions on matter export efficiency, and illustrate the tight link between the specific composition ofphytoplankton communities and the biogeochemical properties characterizing the study area.