Effects of diel CO₂ cycles on the early development and behaviour of coral reef fishes under ocean acidification
Jarrold, Michael D. (2018) Effects of diel CO₂ cycles on the early development and behaviour of coral reef fishes under ocean acidification. PhD thesis, James Cook University.
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Abstract
Increasing atmospheric CO₂ levels are causing a reduction of ocean surface water pH and shift in carbonate chemistry, a process termed ocean acidification. Ocean acidification poses a major threat to marine ecosystems, with a large body of work documenting negative effects of elevated CO₂ on a diverse range of shallow water coastal marine species. However, most studies to date have used stable CO₂ treatments, not considering the substantial diel CO₂ variation that occurs in many shallow water marine habitats. This thesis investigates how the presence of diel CO₂ cycles modifies the early development and behaviour of coral reef fishes under elevated CO₂, and how the effects of diel CO₂ cycles are further modified by elevated temperature and parental effects.
In chapter 2 I investigate the interactive effects of elevated CO₂ and diel CO₂ cycles on juvenile survival, growth and otolith development in two species of coral reef fish. There was no effect of CO₂ treatment on survival and otolith development of Acanthochromis polyacanthus or Amphiprion percula. While growth was not significantly affected by CO₂ treatment in either species, there was a trend for fish reared under diel-cycling elevated CO₂ to be more similar in size to control fish, compared to those reared under stable elevated CO₂. These results suggest that the early development of juvenile coral reef fishes under future ocean acidification conditions is unlikely to be affected by diel cycles in CO₂.
The behavioural alterations that have been observed in coral reef fishes under elevated CO₂ are likely to interact with diel CO₂ cycles, due to the concentration-dependent effects that stable elevated CO₂ has on onset times and the magnitude of behavioural impairments. Therefore, chapter 3 investigates the effects that diel CO₂ cycles have on behavioural lateralization in A. polyacanthus and response to a predator cue in Am. percula under elevated CO₂. As expected, exposure to stable elevated CO₂ caused behavioural impairments in both species. However, diel CO₂ cycles substantially reduced the severity of behavioural abnormalities caused by elevated CO₂ and in some cases fully alleviated the negative effects. These results highlight that past studies may have over-estimated the impacts of ocean acidification on the behavioural performance of coral reef fishes, because they did not include natural CO₂ cycles in the ocean acidification treatments.
The responses of shallow water marine organisms to ocean acidification can be altered by elevated temperature. In chapter 4 I tested whether the interaction between elevated CO₂ and diel CO₂ cycles is further modified by elevated temperature. Survival, growth and behavioural traits were measured in juvenile A. polyacanthus. A significant interaction between CO₂ treatments and temperature was only detected for survivorship. Survival was lower in the two diel-cycling elevated CO₂ treatments, but only when temperature was elevated. In other traits, independent effects of elevated CO₂, and interactions between elevated CO₂ and diel CO₂ cycles were detected, but these effects were not influenced by temperature. Elevated temperature had significant, negative effects on most traits measured. Overall, the results of this chapter demonstrate that while elevated temperature had a stronger effect on most traits it did not alter the interactive effects elevated CO₂ and diel CO₂ cycles had on growth and behavioural traits.
Previous studies have shown that parental exposure to elevated CO₂ can mitigate negative effects of elevated CO₂ on juvenile growth and survival. However, the outcome of parental effects in the presence of diel CO₂ cycles may differ from those expressed in a stable CO₂ environment. To test this, chapter 5 investigates the effects that parental exposure to stable elevated and diel-cycling elevated CO₂ had on the survival and growth of juvenile anemonefish, Am. melanopus. Within-generation exposure to stable elevated CO₂ caused a significant reduction in juvenile growth; however, there was no effect of elevated CO₂ on juvenile growth when diel CO₂ cycles were present in the juvenile elevated CO₂ treatment, or when parents had experienced the same conditions as the juveniles (either stable elevated and diel-cycling elevated CO₂). Additionally, parental exposure to diel CO₂ cycles did not alter the effects of diel CO₂ in juveniles. These results illustrate the importance of considering natural CO₂ cycles when predicting the long-term impacts of OA on marine ecosystems.
The research presented here is among the first to test how natural CO₂ cycles in shallow water habitats affect the performance of marine fishes under ocean acidification. The results show that the performance of coral reef fishes under elevated CO₂ is enhanced when a diel-cycling CO₂ regime is present. Future studies should investigate the underlying mechanisms responsible for the observed improvements under diel-cycling elevated CO₂. Additionally, CO₂ is the not the only environmental parameter to fluctuate daily in shallow coral reef habitats. Diel cycles in temperature also exist and thus future work should also incorporate fluctuating temperature treatments. Overall, this body of research highlights the critical importance of incorporating natural environmental variability into experiments to accurately assess the responses of shallow water coastal marine organisms to future ocean conditions.
| Item ID: | 58925 |
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| Item Type: | Thesis (PhD) |
| Keywords: | acclimation, activity, CO2 fluctuations, coral reef fishes, daily fluctuations, fast starts, lateralization, ocean acidification, ocean warming, parental effects, pH variability, phenotypic plasticity |
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| Copyright Information: | Copyright © 2018 Michael D. Jarrold. |
| Additional Information: | Publications arising from this thesis are available from the Related URLs field. The publications are: Chapter 2: Jarrold, Michael D., and Munday, Philip L. (2018) Diel CO2 cycles do not modify juvenile growth, survival and otolith development in two coral reef fish under ocean acidification. Marine Biology: international journal on life in oceans and coastal waters, 165 (3). 49. Chapter 3: Jarrold, Michael D., Humphrey, Craig, McCormick, Mark I., and Munday, Philip L. (2017) Diel CO2 cycles reduce severity of bahavioural abnormalities in coral reef fish under ocean acidification. Scientific Reports, 7. Chapter 4: Jarrold, Michael D., and Munday, Philip L. (2018) Elevated temperature does not substantially modify the interactive effects between elevated CO2 and diel CO2 cycles on the survival, growth and behavior of a coral reef fish. Frontiers in Marine Science, 5. 458. Chapter 5: Jarrold, Michael D., and Munday, Philip L. (2019) Diel CO₂ cycles and parental effects have similar benefits to growth of a coral reef fish under ocean acidification. Biology Letters, 15 (2). 20180724. |
| Date Deposited: | 15 Jul 2019 23:17 |
| FoR Codes: | 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 30% 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 35% 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 35% |
| SEO Codes: | 96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 50% 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50% |
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