Responses of hard corals and competing reef organisms to ocean warming, nutrient enrichment, and mitigation interventions

Hard-coral dominated reefs provide essential ecosystem services and support marine biodiversity. However, these reefs are increasingly threatened by global factors such as ocean warming, exacerbated by local factors such as nutrient enrichment. As hard coral cover declines, alternative benthic organisms, including soft corals and turf algae, dominate the newly available substrate, thereby reducing structural complexity, hindering coral recruitment, and impairing critical reef functions. Comparative studies are therefore essential to fully understand the differences between the responses of hard corals and alternative benthic organisms to environmental change. Yet, studies of this nature remain limited. Additionally, proactive interventions are needed to support hard coral resilience. Therefore, this thesis addresses these critical knowledge gaps, focusing on: (1) comparing the thermal tolerance of key benthic reef organisms, (2) investigating the interactive effects of heat stress and nutrient enrichment, in particular the influence of different nitrogen:phosphorus (N:P) ratios, and (3) testing the efficacy of potential stress antagonists to support hard coral resilience and recovery, via both field and laboratory experiments.