Net ecosystem production of coral communities persisting under marginal environmental conditions

Coral communities in Hong Kong persist under a range of local stressors, including strong subtropical seasonality, chronic low light, and high turbidity, resulting in patchy, compositionally constrained communities relative to typical tropical reef systems. These challenging environmental conditions provide an opportunity to better understand how coral ecosystems may respond to changing ocean conditions in the future. Here, we used in-situ sensors to quantify high-resolution, community-scale net ecosystem production (NEP, organic carbon cycling) at three sites across a marine environmental gradient around Hong Kong. These communities were net respiring (negative NEP) across the gradient in both the wet (NEPmean=-0.49±4.83 mmolO2m-2h-1) and dry seasons (NEPmean=-0.21±0.85 mmolO2m-2h-1), with a significant increase in metabolic variability observed during the wet season (mean daily NEP range=9.99±13.34 mmolO2m-2h-1) versus the dry season (2.38 ± 1.93 mmolO2m-2h-1), associated with stronger variation in light and hydrographic conditions. This study adds to the small number of studies to date assessing in-situ metabolic variability of coral communities persisting under marginal environmental conditions. Understanding natural community-scale variability in organic carbon cycling is crucial for predicting how coral communities may cope with changing ocean conditions, thereby providing vital insights into the future of globally threatened coral ecosystems.