| Summary: | Maerl beds located in coastal systems are affected by local changes that may compromise their survival and resilience to global change (ocean warming and acidification). Despite the increasing knowledge regarding the contribution of coralline algae to the carbon and carbonate cycles, and their response to future scenarios of global change, there is a lack of information regarding how they are currently impacted by local changes. This thesis sought to evaluate: i) how three temperate maerl beds (Brittany, France) are impacted by local changes (field study), and ii) how three of the most abundant maerl species in the NE Atlantic (Lithothamnion corallioides, Phymatolithon calcareum and Lithophyllum incrustans) are impacted by ocean warming and acidification (according to the scenario RCP8.5, +2.7ºC and -0.3 pH units) (laboratory study). Field observations in the Bay of Brest showed that the heterogeneity and seasonality of the macroalgal living biomass and primary production is marked by local changes. Freshwater inputs from rivers into the Bay of Brest exacerbated the dissolution of L. corallioides thalli in the dark. Laboratory observations displayed species-specific responses with a more negative impact of global change under winter conditions compared to summer conditions, and an interaction of effects of global change with other abiotic parameters such as nutrient availability and light intensity. The results of this thesis highlight the impact of local changes due to natural and anthropogenic influences on the development, survival and capacity of maerl beds to adapt to global change. Les bancs de maërl situés dans des écosystèmes côtiers sont soumis à l’impact des changements locaux qui peuvent affecter leur capacité à s’adapter/s’acclimater au changement global (réchauffement et acidification des océans). Malgré l’accroissement de nos connaissances concernant la contribution des algues corallinacées aux cycles du carbone et du carbonate et leur réponse au changement global, un manque de connaissances ...
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