Effets combinés du rayonnement ultraviolet et du réchauffement climatique sur les coraux Scléractiniaires

Abstract : Scleractinian corals mainly grow in the shallow euphotic zone, exposed to ultraviolet radiation (UVR), the most harmful part of the solar radiation. UVR increases with climate change and adds to the different environmental pressures that corals are facing. The aims of this thesis were to 1) better understand the effects of UVR on coral physiology, organic matter fluxes and associated bacteria; 2) assess the combined effects of UVR and thermal stress and/or nutrient level. Results show that UVR worsens the negative effect of temperature on coral physiology, similarly to nutrient depletion. Our results also indicate that the sensitivity to UVR stress (i.e. an increase in UVR) is species dependent and function of the symbiont density. The negative effects of UVR increase with the number of symbionts, likely due to the formation of reactive oxygen species (ROS) which cause cellular damages. In the thesis, we showed that the JNK signalling pathway (c-Jun N-terminal kinase), highly conserved in living organisms, is involved in the early response of corals to UVR and its activation is required to repress stress-induced ROS accumulation. Finally, organic matter release and mucus and coral-associated bacteria are also significantly impacted by UVR, which could contribute to important biochemical changes in reef waters. The work conducted in this thesis brings new insights into the effects of UVR on corals and highlights the importance of taking this environmental factor into account when predicting the future of coral reefs under climate change.
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Lucile Courtial. Effets combinés du rayonnement ultraviolet et du réchauffement climatique sur les coraux Scléractiniaires. Milieux et Changements globaux. Université Pierre et Marie Curie - Paris VI, 2017. Français. ⟨NNT : 2017PA066214⟩. ⟨tel-02301986v2⟩

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