15. The Effects of Natural CO2 Variability on Behavioural Sensitivity of Coral Reef Fish to Ocean Acidification

Michael D. Jarrold (1,2)* and Philip L. Munday (2)

1 College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia.
2 ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4814, Australia.

Background
Sensory performance and behavioural responses of coral reef fishes are impaired by CO2 levels projected to occur by the end of the century. However, coral reefs also experience daily CO2 fluctuations that can be greater than the projected increase in CO2 levels this century. Experiments to-date on behavioural effects of high CO2 have used steady-state treatments. It is therefore unknown how natural CO2 fluctuations will interact with rising mean CO2 levels to affect the behavioural sensitivity of coral reef fishes to ocean acidification.

Methods
We will rear juvenile damselfish, Acanthochromis polyacanthus, under a series of stable (450, 750, and 1050 µatm) and daily fluctuating CO2 treatments (450 ± 150 and 300 µatm, 750 ± 150 and 300 µatm and 1050 ± 300 and 600 µatm) for 10-14 days. After this period we will test their ability to recognise chemical alarm cues and escape responses; both important predator avoidance behaviours essential for daily survival. Testing these behaviours will enable us to determine how natural fluctuations in CO2 will affect olfactory (chemical alarm cue trials) and cognitive/locomotory (escape response trials) performances.

Findings
We predict that behavioural responses will not be impaired under fluctuating treatments, where CO2 levels drop below 600 µatm; the minimum level at which sensory and behavioral impairments have been observed. This prediction is based on evidence that it takes between 2-4 days of constant exposure to elevated CO2 levels for behavioural abnormalities to develop.

Conclusions
The results from our study will shed light on whether experiments incorporating natural fluctuations in CO2 are needed to more reliably predict the impacts of rising CO2 on shallow water marine organisms.