Navigating the challenges of urbanization and turbidity: ecological implications and management strategies for coral reef ecosystems

Coastal urbanization poses severe challenges to coral reef ecosystems, leading to habitat degradation, reduced biodiversity, and altered ecological dynamics. This thesis investigates the impacts of urban stressors, including turbidity, on coral reef dynamics and processes in Indonesia. The research, structured into seven studies, reveals six key findings: (1) Turbidity and island-based activities are key stressors on Spermonde Archipelago reefs, with severe turbidity limited to approximately 5 km from the mainland and decreasing offshore. (2) A notable shift from coral-dominated to algae-dominated habitats has occurred over the past two decades, with distinct spatial variability in benthic and reef fish conditions across the archipelago. (3) Turf algae dynamics reveal a clear inshore-to-offshore gradient, with bottom-up mechanisms driving turf algae growth more strongly than top-down control mechanisms. (4) Urban stressors significantly impact reef fish dynamics, with more diverse and abundant fish communities in clearer, shallower middle-to-offshore reefs, and herbivory playing a crucial role in maintaining reef health. (5) Coral reef resilience in the face of rapid urbanization is influenced by a complex interplay of strengthening and weakening factors, with some positive adaptations observed but also challenges from urban stressors and limited functional redundancy. (6) Marine protected areas (MPAs) and other effective area-based conservation measures (OECMs) offer potential strategies for managing urban reefs, but must be integrated with broader management approaches addressing land-based impacts. The study underscores the urgent need for comprehensive management approaches to mitigate the accelerating degradation of urban coral reefs, ensuring the conservation of biodiversity and essential ecosystem services.