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:

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:



  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).

Ocean Acidification Part 1: Reduce our carbon footprint for coral reefs

Blog post by: Regan Jade

Did you know that your daily actions are contributing to the changing chemistry of our oceans?

Coral reefs are incredibly important; they are some of the most biologically rich and economically valuable ecosystems on Earth. They provide food, jobs, income, and protection to billions of people worldwide (2).

However, our actions are threatening our beautiful coral reefs.

Humans are burning fossil fuels and releasing carbon dioxide into the earth’s atmosphere at unprecedented levels (1); this rise in carbon dioxide is a big problem as more than 25% of it is absorbed by our oceans and causing them to increase in acidity. This is termed ocean acidification.  And it’s a big problem for our coral reefs.

The problem with ocean acidification

Most marine organisms are adapted to  a relatively stable ocean pH; however since pre-industrial times, ocean acidity levels have increased by 30%.  Research suggests future ocean acidification rates could be higher than anything experienced in the previous 65 million years (3).

When the ocean increases in acidity, marine organisms like corals and crustaceans find it very difficult to build their shells and skeletons. This is because these organisms use calcium carbonate, the same material that chalk and limestone are made of, to form their shells. Calcium carbonate is typically abundant in seawater, but as the ocean becomes more acidic, it becomes less abundant. This decreases the ability of marine organisms to create structures to sustain their lives, including corals who also create habitat for a large proportion of marine life (4).

Need more convincing? Check out this video of Hermie and his reality with ocean acidification (also a great video to show the kids)


Carbon emissions on the rise

Human activity since the Industrial Revolution has increased carbon dioxide levels in our atmosphere from 280 parts per million to 400 parts per million. The last time carbon dioxide levels were this high for a sustained period of time was 2 – 4.6 million years ago (5). Carbon emissions caused by humans come from many sources, including the burning of fossils fuels like coal, oil and gas; deforestation, agriculture, and the production of plastic.

By reducing your carbon emissions, you can help our coral reefs. It may seem like the issue is too much to tackle as an individual but we can all make a difference with our daily actions.

Five things you can do to reduce your carbon emissions and help our coral reefs

  • Drive your car less: The burning of fossils fuels is a major contributor to carbon emissions. Can you bike to work? Take public transport or carpool with your work mates?
  • Eat locally: How far has your food traveled? Reduce your carbon emissions by opting for local produce instead of produce that has been shipped from overseas.
  • Conserve your energy use at home and switch to green energy: Turn off lights when you are not in the room, switch off power points and swap to a green energy provider like Power Shop (6).
  • Reduce your plastic use: Carbon dioxide enters the atmosphere through burning fossil fuels like oil and gas (7). Many Plastics are made from oil and gas so choose to reuse instead, recycle where possible and avoid single-use plastic.
  • Monitor your local reefs: Become a reef searcher with reef check so you can monitor the health of your local reefs over time.

Start with one action at a time and keep building on your new habits when you can. What action will you start with today to help our coral reefs? Let us know in the comments.



(1) The threat of ocean acidification to ocean ecosystems – John Guinotte and Victoria J Fabry