Ocean Acidification Part 2: What’s that fishy smell?

Blog post by: Meg Welch

In our last post we learned that ocean acidification makes life more difficult for marine life with calcium carbonate skeletons or shells, like corals and crustaceans. But did you know that ocean acidification also affects fish? Research is consistently finding that fish behaviour changes when seawater becomes more acidic. Fish show increased activity levels, an impaired ability to learn, and changes to their senses of hearing and smell1-3. Many of these changes have significant consequences on predator-prey interactions4,5, competition and habitat selection6.

Fish swimming in a natural carbon dioxide seep in Papua New Guinea. Photo by Alistair Cheal.

When fish experience high CO2 levels predicted for the next 100 years7 for more than four days, they become attracted to predator odours and chemical alarm cues that they would avoid under present-day circumstances. This means that fish willingly put themselves in harm’s way, increasing their death toll. This raises concerns about the ability of fish populations to maintain themselves in the predicted high CO2 world. A few longer-term experiments and studies at natural CO2 seeps indicate that after many weeks to months of high CO2 exposure, fish behaviour remains impaired8.

What’s behind these changes?

It is believed that these behavioural changes in fish are largely due to a chemical fluctuation in the brain that occurs when fish are exposed to high levels of CO29. This action occurs in the GABA-A receptor, whose job is to reduce the activity of brain cells, called neurons, and prevent overstimulation. The changes in ocean chemistry brought on by high levels of CO2 cause changes in the fish blood and tissue, which leads to the abnormal functioning of the GABA-A receptor. This is similar to epilepsy in mammals.

What does this mean for future fish?

While research suggests that individual fish may not be able to change their behaviours back to normal in a high CO2 environment, it is important to consider how all environmental factors such as higher temperatures that will occur simultaneously with rising CO2 levels will affect fish. New research must also consider multiple generations, as CO2 levels will rise over the next 100 years, possibly allowing species enough time to adjust to climate change.

This field of research truly burns with the anticipation for the future. You can keep up to date with the most recent research on ocean acidification by signing up to this list-serve. Stay tuned for new research about fish in a changing environment!

How you can help

You can help fish smell correctly by helping to reduce CO2 emissions. Follow these easy steps to make a difference:

1. Measure your carbon footprint here: http://www.nature.org/greenliving/carboncalculator/

2. Reduce your emissions by carpooling or taking public transport. Our last post had a few more great ideas to help reduce energy consumption as well!

3. If you see anything odd while you’re out swimming, diving or fishing, send a note to Redmap: http://www.redmap.org.au/



  1. Briffa, M., et al. High CO2 and marine animal behaviour: Potential mechanisms and ecological consequences. Mar. Pollut. Bull. 64, 1519-1528 (2012).
  1. Branch, T. A., et al. Impacts of ocean acidification on marine seafood. Trends Ecol. Evol. 28, 178-186 (2013).
  1. Leduc, A. O. H. C., et al. Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: A synthesis. Phil. Trans. R. Soc. B 368, 20120447 (2013).
  1. Munday, P. L., et al. Replenishment of fish populations is threatened by ocean acidification. Proc. Natl. Acad. Sci. USA 107, 12930-12934 (2013).
  1. Ferrari, M. C. O., et al. Putting prey and predator into the CO2 equation- qualitative and quantitative effects of ocean acidification on predator-prey interactions. Ecol. Lett. 14, 1143-1148 (2011).
  1. Munday, P. L., et al. Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proc. Natl. Acad. Sci. 6, 1848-1852 (2009).
  1. Collins, M., et al. Long-term climate change: projections, commitments and irreversibility. In: Stocker, T. F., et al. (eds) Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, USA, pp 1096-1097 (2013).
  1. Munday, P. L., et al. Behavioural impairment in reef fishes caused by ocean acidification at CO2 seeps. Nature Clim. Change 4, 487-492 (2014).
  1. Nilsson, G. E., et al. Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function. Nature Clim. Change 2, 201-204 (2012).

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