Re-evaluating relationships between calcification and production in dynamic coral reef ecosystems

Linear regressions between total alkalinity (TA) and dissolved inorganic carbon (DIC) are widely used to infer the balance between net ecosystem calcification (NEC) and net ecosystem production (NEP) in coral reefs. Using high-frequency carbonate chemistry observations from an Australian reef flat and simple numerical models, we show that TA–DIC slopes primarily reflect the temporal co-variability of NEC and NEP, rather than their time-integrated metabolic balance. To recover time-integrated metabolic information, diel reef measurements must be coupled with offshore reference conditions, which anchor changes in TA and DIC to NEC:NEP ratios. We further demonstrate that apparent metabolic balance shifts systematically over the diel cycle and depends on light, indicating that it is inherently dynamic rather than static. Together, our results highlight the need to distinguish metabolic co-variability from metabolic ratios when interpreting carbonate chemistry data in coral reef and other dynamic aquatic ecosystems.