Coral communities provide habitat, coastal protection, and fisheries support but are increasingly threatened by global climate change and local anthropogenic pressures. These stressors disrupt key ecological and biogeochemical processes, undermining coral persistence and ecosystem function. Oxygen is the fundamental currency of community metabolism, linking photosynthesis, respiration, and calcification. Its availability influences biodiversity, coral bleaching sensitivity, and competitive dynamics. This thesis investigates the natural spatiotemporal variability in oxygen dynamics and community metabolism across coral environments that persist near or beyond typical tolerance limits – specifically in marginal systems, where ecological conditions challenge structural integrity, and extreme systems, where environmental conditions routinely exceed optimal thresholds. Natural spatiotemporal variability in metabolism and oxygen dynamics was examined across three spatial scales. Firstly, we quantified net ecosystem production (NEP) and net ecosystem calcification (NEC) across an estuarine–urbanisation gradient (~20 km) around Hong Kong. All sites were net respiring and net dissolving, but spatial and seasonal differences in NEP and NEC were linked to local hydrodynamics and benthic composition. Next, diel oxygen dynamics were examined around Sharp Island (~1 km scale), revealing frequent nighttime hypoxia in areas with high coral cover and divergent ecological trajectories following a typhoon and storm-induced hyposalinity event. Finally, we focused on a reef slope (<1 km) at Dongsha Atoll, where internal waves and typhoons drive extreme thermal and biogeochemical variability. Interactions between internal waves and a strong typhoon triggered a depth-constrained phytoplankton bloom, and organic matter respiration during tidal flows may drive hypoxia in inner lagoon areas. By integrating observations across marginal and extreme coral communities, this thesis highlights how local biophysical variability and large-scale oceanographic forcing interact to shape ecosystem metabolism. Understanding these dynamics is essential for predicting the function and resilience of coral communities in a rapidly changing ocean.