Diel CO2 cycles do not modify juvenile growth, survival and otolith development in two coral reef fish under ocean acidification

Abstract

Recent studies show that daily variation in pCO2 levels can modify the life-history and calcification responses of marine organisms to ocean acidification. The early life stages of coral reef fish exhibit varied growth, survival and otolith development responses to elevated pCO2, yet no studies to date have considered the substantial diel pCO2 cycles that occur in shallow reef habitats. Here, we reared three clutches of juvenile Acanthochromis polyacanthus and Amphiprion percula under control (500 µatm), stable, elevated (1000 µatm) and diel cycling, elevated (1000 ± 300 and 1000 ± 500 µatm) pCO2 for 11 and 6 weeks, respectively. Survival was unaffected by exposure to either elevated stable or diel cycling pCO2 conditions in both species. For A. polyacanthus there was a non-significant trend of decreased standard length and wet weight under stable, elevated pCO2 conditions, whereas values in both the diel cycling treatments were closer to those observed under control conditions. A similar non-significant trend was observed for Am. percula, except that exposure to stable, elevated pCO2 conditions resulted in slightly longer and heavier fish. Finally, otolith size, shape and symmetry in both species were unaffected by exposure to either elevated stable or diel cycling pCO2 conditions. Overall, our results suggest that the growth, survival and otolith development of juvenile coral reef fishes under ocean acidification is unlikely to be affected, in isolation, by diel cycles in pCO2.