Les Particules d'Exopolymères Transparentes (Transparent Exopolymer Particles, TEP) en milieu pélagique lacustre : relation avec le phytoplancton et rôle dans les réseaux trophiques microbiens

Abstract : This work adds to the knowledge of the significance of polysaccharidic detrital particles or TEP (= Transparent Exopolymer Particles) in freshwater pelagic environments. Studies in this thesis have mainly focused on the distribution of TEP and their relationships with phytoplankton and other microorganisms in natural environments (the oligo-mesotrophic Lake Pavin and the hypereutrophic reservoir of Grangent) and in limnetic enclosures (lake of Créteil). The intensity of bacterial colonization during spring in Lake Pavin was strongly related to temperature and decreased with particle size. The abundance of heterotrophic nanoflagellates (HNF) in this lake was more significantly related to the density of the particles than to the density of total bacteria and the intensity of bacterial colonization of TEP, suggesting that TEP is a more important factor for HNF development than attached and free bacteria. The abundance and the total surface area of the particles were significantly higher in the hypereutrophic Lake Grangent than in the mesotrophic Lake Pavin. Maximum TEP density in Lake Pavin was recorded during the spring diatom bloom, while TEP concentration peaked in late summer when the phytoplankton community was largely dominated by small-size chlorophytes with an abundant polysaccharide cell coating. In the hypereutrophic Lake Grangent,maximum values of TEP appeared during the summer development of the cyanobacterium Microcystis aeruginosa. Per cell production of TEP, expressed by the ratio between TEP concentration and chlorophyll a concentration, was significantly higher in the less productive lake and the analysis of the size spectra of the particles indicated a greater proportion of small particles in this lake. TEP therefore appear as more significant for microbial development and aggregates formation in the less productive environment. Results from limnetic enclosures (either dominated by planktivorous fish or fishless) indicated that food-web structure strongly influences the distribution and size spectra of TEP. TEP abundances were related to chlorophyll a concentrations and the biomass of chlorophytes in the fish treatment. As expected by the trophic cascades theory, zooplankton had an indirect negative effect on TEP abundance. Our results suggest, however, that metazoan probably influence the formation and the size spectra of the particles in the fishless treatment. TEP must be regarded as a major part of the organic carbon which is transferred from the primary producers to the microbial food web and the sediments in freshwater ecosystems.
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Mohamad Bashir Arnous. Les Particules d'Exopolymères Transparentes (Transparent Exopolymer Particles, TEP) en milieu pélagique lacustre : relation avec le phytoplancton et rôle dans les réseaux trophiques microbiens. Sciences agricoles. Université Blaise Pascal - Clermont-Ferrand II, 2010. Français. ⟨NNT : 2010CLF22066⟩. ⟨tel-00629661⟩

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