Diel CO2 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 CO2 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) CO2 had on the survival and growth of juvenile coral reef anemonefish, Amphiprion melanopus. Juvenile survival was unaffected by within-generation exposure to either elevated CO2 treatment but was significantly increased (8%) by parental exposure to diel-cycling elevated CO2. Within-generation exposure to stable elevated CO2 caused a significant reduction in juvenile growth (10.7-18.5%); however, there was no effect of elevated CO2 on growth when diel CO2 cycles were present. Parental exposure to stable elevated CO2 also ameliorated the negative effects of elevated CO2 on juvenile growth, and parental exposure to diel CO2 cycles did not alter the effects of diel CO2 cycles on juveniles. Our results demonstrate that within-generation exposure to diel-cycling elevated CO2 and parental exposure to stable elevated CO2 had similar outcomes on juvenile condition. This study illustrates the importance of considering natural CO2 cycles when predicting the long-term impacts of OA on marine ecosystems.