Frameworks for seaweed forest restoration in the context of environmental change

Abstract

Restoration efforts have increased worldwide, but threats to the maintenance of seaweed forests are increasing. This thesis focuses on four aspects of conservation and restoration research needed to future-proof seaweed forests in the context of environmental change: (i) recognising the capacity to scale-up restoration, (ii) increasing knowledge of the reproductive patterns of the target species, (iii) determining the vulnerability and resilience to marine heatwaves, and (iv) developing biobanking protocols to secure genetic diversity. I used Phyllospora comosa as a case study, which is an ecologically important forest-forming fucoid seaweed in southeastern Australia. Utilising long-term data from restoration interventions across multiple sites in Sydney, I first evaluated the capacity of small-scale restoration efforts to re-establish Phyllospora populations that match the spatial scale of degradation. Second, I described the seasonal reproductive patterns in Phyllospora; such knowledge is essential for increasing re-establishment success and for developing climate-mitigation strategies that require gamete and germling production (e.g., assisted evolution and cryopreservation). Third, I conducted a mesocosm experiment to evaluate the vulnerability of early life-stages from warm-edge and central populations of Phyllospora to marine heatwaves (MHWs), which are a major threat to the maintenance of seaweed forests Fourth, I developed new cryopreservation protocols to protect Phyllospora genetic diversity, a critical need due to the risk of permanent loss in certain populations. Overall, this thesis emphasises the need for basic research before implementing conservation efforts. My results contribute to improving the outcomes of conservation and provide pathways to enhance the resilience of Phyllospora, serving as a guideline for future-proofing restoration and conservation of this and other forest-forming seaweeds in the context of environmental change.