Reproductive-state and life-stage variation in oxyregulation of reef-building corals

Accelerating ocean deoxygenation driven by anthropogenic warming, eutrophication, and water column stratification poses a global threat to coral reef ecosystems. Several large-scale coral mortality events have been documented on reefs in response to periods of severe hypoxia, wherein environmental dissolved oxygen (DO) levels are insufficient for maintaining physiological homeostasis and supporting coral health. Although adult corals have the capacity for oxyregulation, the extent to which such capacity is affected by reproduction or during coral larval life stages remains poorly understood. Here, we examined oxygen consumption patterns of eight coral species and the offspring of four of these species using closed system respirometry to characterise oxyregulatory performance before and after spawning. Adult corals exhibited a significant increase in oxyregulatory capacity, exerting their maximum regulation capacity (Pcmax) at a lower DO partial pressure (pO2) one week following spawning relative to the 1–2 days preceding gamete release, indicating heightened vulnerability of gravid colonies to hypoxia. Coral larvae also exhibited capacity for oxyregulation, albeit at a lowered capacity (i.e., less regulation possible above oxyconformity based on total positive regulation, Tpos) compared to adults, and larval performance did not correlate with conspecific adult responses. These results highlight ontogenetic and reproductive-state oxyregulation variability, suggesting critical variation in metabolic responses to DO availability across life stages. Characterising coral life stage-specific responses to altered DO availability provides important physiological context for understanding how coral reef organisms may respond to ongoing and future ocean deoxygenation.