Climate change threats to Mediterranean bioconstructors: trait-based approach for assessing coralligenous responses to extreme climatic events

Global warming and extreme climatic events are significantly affecting marine ecosystems structure and functioning, with Mediterranean coralligenous habitats being especially vulnerable due to the nature of their life history and functional traits. Throughout six different chapters, this PhD thesis investigated the impacts of multiple human-driven climatic stressors on the functioning of coralligenous and pre-coralligenous habitats. Scaling from the individual to the community levels, the integration of mechanistic, modelling and social science approaches allowed for addressing the potential effects of stressors on ecosystem functioning and services. The thesis addressed significant ecological questions related to a deeper understanding of climate change impacts on marine biodiversity, filling critical knowledge gaps, and providing insights for conservation strategies. Some of the main goals achieved include: i) the creation of a consistent ecological baseline for coralligenous community characterization and conservation status along the southwestern Italian coast, ii) a deeper understanding of the eco-physiological mechanisms underlying vulnerability to thermal stress and the role in carbon sequestration process of Eunicella singularis meadows; iii) the distribution and functional responses of Astroides calycularis reefs to extreme climatic events, highlighting the importance of stressor properties in species and population responses; and iv) the experimental identification of the thermal tolerance and niche overlap of the interacting species A. calycularis and the predator Hermodice carunculata (bearded fireworm), revealing a potential increase in predation pressure on the coral under warming scenarios. By combining scientific methodologies with stakeholder engagement, this work offered a comprehensive trait-based framework for preserving vulnerable Mediterranean coastal ecosystems.