Diel CO cycles and parental effects have similar benefits to growth of a coral reef fish under ocean acidification.

Parental effects have been shown to buffer the negative effects of within-generation exposure to ocean acidification (OA) conditions on the offspring of shallow water marine organisms. However, it remains unknown if parental effects will be impacted by the presence of diel CO cycles that are prevalent in many shallow water marine habitats. Here, we examined the effects that parental exposure to stable elevated (1000 µatm) and diel-cycling elevated (1000 ± 300 µatm) CO had on the survival and growth of juvenile coral reef anemonefish, Amphiprion melanopus. Juvenile survival was unaffected by within-generation exposure to either elevated CO treatment but was significantly increased (8%) by parental exposure to diel-cycling elevated CO. Within-generation exposure to stable elevated CO caused a significant reduction in juvenile growth (10.7-18.5%); however, there was no effect of elevated CO on growth when diel CO cycles were present. Parental exposure to stable elevated CO also ameliorated the negative effects of elevated CO on juvenile growth, and parental exposure to diel CO cycles did not alter the effects of diel CO cycles on juveniles. Our results demonstrate that within-generation exposure to diel-cycling elevated CO and parental exposure to stable elevated CO had similar outcomes on juvenile condition. This study illustrates the importance of considering natural CO cycles when predicting the long-term impacts of OA on marine ecosystems.