Community-scale metabolism of coral ecosystems persisting under marginal environmental conditions

Abstract. Coral communities in Hong Kong persist under a range of natural and anthropogenic stressors, including strong seasonality, high bioerosion, sedimentation, and elevated nutrient levels. These challenging environmental conditions provide an opportunity to better understand how coral ecosystems may adapt 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 (NEP_mean= −0.49 ± 4.83 mmol O₂ m⁻² hr⁻¹) and dry seasons (NEP_mean= −0.21 ± 0.85 mmol O₂ m⁻² hr⁻¹), with a significant increase in metabolic variability observed during the wet season (mean daily NEP range = 9.99 ± 13.34 mmo O₂ m⁻² hr⁻¹) versus the dry season (2.38 ± 1.93 mmol O₂ m⁻² hr⁻¹) . This study is the first to our knowledge to assess in-situ metabolic variability of coral communities persisting under marginal environmental conditions. Understanding natural community-scale variability is crucial for predicting how coral communities may adapt to changing ocean conditions, thereby providing vital insights into the future of globally threatened coral reef ecosystems.