Diel p CO 2 fluctuations alter the molecular response of coral reef fishes to ocean acidification conditions

• Published in: Molecular Ecology
• Main Authors: Schunter, Celia, Jarrold, Michael D., Munday, Philip L., Ravasi, Timothy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1111/mec.16124; https://onlinelibrary.wiley.com/doi/pdf/10.1111/mec.16124; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/mec.16124; https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/mec.16124

Abstract Environmental partial pressure of CO 2 ( p CO 2 ) variation can modify the responses of marine organisms to ocean acidification, yet the underlying mechanisms for this effect remain unclear. On coral reefs, environmental p CO 2 fluctuates on a regular day–night cycle. Effects of future ocean acidification on coral reef fishes might therefore depend on their response to this diel cycle of p CO 2 . To evaluate the effects on the brain molecular response, we exposed two common reef fishes ( Acanthochromis polyacanthus and Amphiprion percula ) to two projected future p CO 2 levels (750 and 1,000 µatm) under both stable and diel fluctuating conditions. We found a common signature to stable elevated p CO 2 for both species, which included the downregulation of immediate early genes, indicating lower brain activity. The transcriptional programme was more strongly affected by higher average p CO 2 in a stable treatment than for fluctuating treatments, but the largest difference in molecular response was between stable and fluctuating p CO 2 treatments. This indicates that a response to a change in environmental p CO 2 conditions is different for organisms living in a fluctuating than in stable environments. This differential regulation was related to steroid hormones and circadian rhythm (CR). Both species exhibited a marked difference in the expression of CR genes among p CO 2 treatments, possibly accommodating a more flexible adaptive approach in the response to environmental changes. Our results suggest that environmental p CO 2 fluctuations might enable reef fishes to phase‐shift their clocks and anticipate p CO 2 changes, thereby avoiding impairments and more successfully adjust to ocean acidification conditions.