Cold-water corals such as Lophelia pertusa, a key reef-building species distributed worldwide, provide highly valuable habitats for diverse biological communities. They thrive in water characterized by year-round temperatures ≤ 14°C, and are therefore thought to be particularly threatened by ocean warming. Recent studies have characterised cold-water coral ecology and showed degraded health status in response to temperature changes. However, it is still not clear if populations from different oceanic regions, living under different temperature conditions (i.e., 10°C in the Atlantic and 13°C in the Mediterrannean Sea), respond in similar ways to temperature changes. The general objective of this thesis was to investigate the effects of temperature on NE Atlantic populations of L. pertusa and to test if they share the same thermal ecological niche as Mediterranean populations. In the first section of the thesis (Chapters 2 and 3) we conducted experiments to study the response of L. pertusa holobiont to temperature changes at different time scales. We determined the holobiont’s response by describing the microbiome’s diversity and function and the coral’s physiology (survival, growth, nutrition, gene expression). These experiments showed that NE Atlantic L. pertusa exhibited a large mortality when temperature increased beyond + 3°C. Before death, the corals showed clear signs of stress, and their microbiome changed (dysbiosis) with the invasion of pathogenic bacteria. Inversely, lower water temperature did not affect L. pertusa health conditions. In the second part of the thesis, we conducted in situ studies aiming at increasing our understanding of the reproduction (Chapter 4), the microbiomes (Chapter 5) and the growth (Chapter 6) of cold-water corals from the NE Atlantic Ocean and the Mediterranean Sea, to ultimately find out if climate change would impact differently these two populations. The study of the coral’s reproductive biology in the Mediterranean Sea suggested that L. pertusa spawns seasonally from autumn to early winter, when episodes of dense water cascading are more likely, while Madrepora oculata showed continuous reproduction, as earlier identified for other populations. Another difference between the two coral species is that L. pertusa had a more variable microbiome in both the NE Atlantic and the Mediterranean Sea, with high spatial variability within canyons. Inversely, M. oculata exhibited stable microbiomes across the different regions characterized by a strong association with the bacteria Endozoicomonas. Finally, our first in situ estimations of L. pertusa growth in a canyon of the Bay of Biscay showed that they grow slower than in the Mediterranean Sea. Overall our findings show a very high sensitivity of Atlantic L. pertusa to +3/+4°C increase in temperature, suggesting that they have a lower upper thermal limit than their Mediterranean counterpart. Considering the high sensitivity of L. pertusa from both populations, they appear to have a low resilience and limited long-term capacity for adaptation to increasing temperature in the context of global climate change.