Beneficial effects of diel CO2 cycles on reef fish metabolic performance are diminished under elevated temperature

Highlights

•Coastal habitats and coral reefs often exhibit a diel cycle of pCO2.

•It is unknown how diel-cycling CO2 and temp affect metabolic traits in reef fishes.

•Traits measured were maximal/resting O2 uptake and factorial/absolute aerobic scope.

•Beneficial effect of diel-cycling CO2 on O2Rest and FAS diminished at high temp.

•Studies should use habitat-relevant CO2 cycles/temp to predict biological effects.

Abstract

Elevated CO2 levels have been shown to affect metabolic performance in some coral reef fishes. However, all studies to date have employed stable elevated CO2 levels, whereas reef habitats can experience substantial diel fluctuations in pCO2 ranging from ±50 to 600 μatm around the mean, fluctuations that are predicted to increase in magnitude by the end of the century. Additionally, past studies have often investigated the effect of elevated CO2 in isolation, despite the fact that ocean temperatures will increase in tandem with CO2 levels. Here, we tested the effects of stable (1000 μatm) versus diel-cycling (1000 ± 500 μatm) elevated CO2 conditions and elevated temperature (+2 °C) on metabolic traits of juvenile spiny damselfish, Acanthochromis polyacanthus. Resting oxygen uptake rates (O2) were higher in fish exposed to stable elevated CO2 conditions when compared to fish from stable control conditions, but were restored to control levels under diel CO2 fluctuations. However, the benefits of diel CO2 fluctuations were diminished at elevated temperature. Factorial aerobic scope showed a similar pattern, but neither maximal O2 nor absolute aerobic scope was affected by CO2 or temperature. Our results suggest that diel CO2 cycles can ameliorate the increased metabolic cost associated with elevated CO2, but elevated temperature diminishes the benefits of diel CO2 cycles. Thus, previous studies may have misestimated the effect of ocean acidification on the metabolic performance of reef fishes by not accounting for environmental CO2 fluctuations. Our findings provide novel insights into the interacting effects of diel CO2 fluctuations and temperature on the metabolic performance of reef fishes.

Laubenstein T. D., Jarrold M. D., Rummer J. L. & Munday P.L., in press. Beneficial effects of diel CO2 cycles on reef fish metabolic performance are diminished under elevated temperature. Science of The Total Environment. doi:10.1016/j.scitotenv.2020.139084. Article (subscription required).

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Ocean acidification in the IPCC AR5 WG II

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