Toward a Restoration Protocol for Mediterranean Red Coral: Incorporating Life History Traits, Genetics, Demography, and Experimental Approaches

In recent decades, the cumulative effect of anthropogenic stressors and climate change has raised particular concern for habitat degradation and biodiversity loss. Globally, there is a growing recognition of the urgent need for interventions to address this environmental deterioration. Current understanding suggests that conservation and management efforts alone are often insufficient to halt or reverse the degradation of threatened ecosystems. Consequently, active ecological restoration has emerged as a crucial strategy to address this challenge. Ecological restoration is particularly relevant when dealing with ecosystem-engineering species, which play a pivotal role in shaping the three-dimensional structure of their environments, providing shelter and trophic resources for a diverse array of associated species. Among marine organisms, corals are outstanding for creating Marine Animal Forests by notably shaping the three-dimensional structure of benthic ecosystems. In this PhD thesis, I investigated key bio-ecological processes of a Mediterranean flagship species, Corallium rubrum, in order to improve their current restoration protocols. When planning restoration actions, it is crucial to aim at reintroducing self-sustaining populations that are demographically stable and genetically resilient, ensuring their long-term viability and adaptability to future environmental changes. To this aim, I focused on two key aspects: (1) demography, trying to decode reproduction mechanisms (Chapter 1), and better describe the ecological trajectory of early life history stages of C. rubrum (Chapter 2); and (2) genetics, trying to highlight the importance of incorporating genetic diversity into restoration efforts (Chapter 3). Thanks to an approach that included in-situ and ex-situ experimentations, I described the fertilization mechanisms of C. rubrum by quantifying the influence of male/female distance on fertilization success. This result shed light on the importance of considering ecological thresholds, such as those linked to the density and distribution of transplanted individuals, which can dramatically influence the output of ecological restoration by impairing fertilization success and, consequently, the reproductive output of the transplanted populations. Beyond transplantation, other restoration techniques have recently gained momentum, such as coral breeding. Here, I present the first attempt at developing a breeding protocol for C. rubrum. I show how rearing corals in captivity may offer a viable ecological shortcut to classical transplantation techniques by broadly enhancing the number of individuals available for restocking. Studying early life history stages allowed us to determine the better settlement and growth conditions for this species by comparing settlement success, and growth and survival performance in-situ or ex-situ. In this context, preserving adequate genetic diversity is crucial for ensuring the long-term viability of restored populations, regardless of the method used for restocking damaged populations—whether through transplantation or coral breeding. Recognizing the pivotal role genetic diversity plays in the resilience and adaptability of coral populations to environmental changes, I aimed to develop guidelines for determining the optimal number of donor colonies required to preserve the genetic variability of wild coral populations during restoration efforts. Overall, this thesis represents a comprehensive approach that integrates life history traits, genetics, demography, and experimental approaches to inform and construct new restoration protocols. These findings demonstrate the necessity of considering bio-ecological processes such as successful reproduction or genetic recombination to ensure long-term successful restoration outputs.