The energetic consequences of oxygen fluxes in a coral reef fish

Ocean warming elevates metabolic rates in marine ectotherms but often constrains energetic resources, causing an imbalance between supply and demand. Transient hypoxia is near‐ubiquitous across the world's coral reefs and may exacerbate this imbalance, yet its effects on the energetics of reef fishes remain poorly understood. In this study, we assess the metabolic costs incurred by a cryptobenthic reef fish exposed to oxygen fluxes measured on the world's hottest coral reefs in the Arabian/Persian Gulf. Hypoxia exposure induced an 8.67% increase in aerobic metabolic rate over the 6 h following reoxygenation and resulted in an estimated 2.87% increase in total daily metabolic rate (mg O 2 kg −1 day −1 ). This energetic cost did not coincide with detectable changes in anaerobic metabolism but was accompanied by increased activity during reoxygenation and a strong, acute transcriptomic response in genes related to oxygen‐sensing. Oxygen availability on the reefs declined below the threshold for inducing such energetic costs on over half (56.04%) of the days throughout the summer, potentially leading to substantial cumulative costs. Such energetic costs represent an additional and previously under‐appreciated consequence of hypoxia in coral reef environments that may exacerbate the temperature‐induced mismatches between energy supply and demand, a key balance affecting growth and fitness. Read the free Plain Language Summary for this article on the Journal blog.