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

Linear regressions between seawater total alkalinity (TA) and dissolved inorganic carbon (DIC) are often used to infer the ratio of net ecosystem calcification (NEC) to net ecosystem production (NEP), which together describes the balance between inorganic and organic carbon fluxes in coral reefs. Using high-resolution TA–DIC data from a reef flat near Lizard Island and numerical models, we show that internal spatiotemporal variability can offset TA–DIC slopes from start-end vectors and decouple them from true NEC:NEP ratios. The NEC:NEP ratio exhibited nonlinear behavior over a diel cycle, with large excursions near metabolic transition points that distort its interpretation as a system-level balance. We introduce a revised metric, the metabolic balance (NEC:Mtot), that incorporates total carbon metabolism. Modeling shows that TA–DIC slopes primarily capture how NEC and NEP co-vary through space and time, rather than their integrated metabolic balance, underscoring the influence of diel metabolic variability.