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Seasonality and dynamics of microbial consortia in the Bay of Banyuls

Abstract : In temperate oceans, yearly transitions from winter to spring are accompanied by a phytoplanktonic bloom. Phytoplankton, at the basis of the food chain in the oceans, plays an essential role in biogeochemical cycles as it generates 50\% of the global primary production. A time series established in 2007 at SOLA, a coastal site in the North Western Mediterranean Sea, monitors environmental and biological parameters. In the first chapter, we demonstrated that several microbial amplicon sequence variants (ASVs) displayed yearly rhythmicity, despite stochastic environmental perturbations, inherent to coastal ecosystems. Network analyses, described in the second chapter, revealed that salinity and temperature deeply impacted the microbial community structure. Subnetworks highlighted that persistent ASVs switched their first neighbors depending on environmental perturbations. These observations suggest the existence of functional redundancy in marine microbial communities. In the third chapter, microcosms confirmed that temperature fluctuations strongly affected natural microbial community structure. Picophytoplankton dominated the incubated communities at low temperature, whereas diatoms prevailed at higher temperatures. These results help explain Bathycoccus prasinos peak of abundance every year at the temperature minimum at SOLA. By integrating results from a time series, cell culture and microcosms experiments, this manuscript helps unravel the impact of anthropologically driven climate change on marine microbial communities.
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Stefan Lambert. Seasonality and dynamics of microbial consortia in the Bay of Banyuls. Biodiversity and Ecology. Sorbonne Université, 2019. English. ⟨NNT : 2019SORUS231⟩. ⟨tel-02954125⟩

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