Ocean acidification makes fish more anxious

If you think you’re stressed out about climate change, be glad you’re not a fish. According to a new study, ocean acidification spurred by rising carbon dioxide in the atmosphere could increase fish’s anxiety levels.

As atmospheric CO2 levels increase, some of that CO2 gets absorbed into the ocean’s surface, which in turn makes the water more acidic. Scientists have found that the rising acidity could endanger creatures such as corals and clams. “By contrast, fish were initially believed to be safe,” the study authors write in Proceedings of the Royal Society B. But recent studies have shown that fish may experience effects such as a scrambled sense of smell, interfering with their ability to avoid predators.

The study authors decided to test anxiety levels in rockfish caught off the coast of California. Some fish were kept in normal seawater, and others were kept in acidified seawater. To measure anxiety, the researchers placed the fish in an arena with light and dark zones, as well as a small LEGO figure in the middle. Spending more time in the dark area is thought to be a sign of higher anxiety.

Fish kept for one week in the acidified water spent an average of 750 seconds in the dark zone and only 150 seconds in the light zone. In contrast, the fish kept in normal water spent about equal amounts of time in the light and dark zones.

To see whether the effect was reversible, the researchers put the fish exposed to acidified water back into normal seawater. After one week, the fish still preferred the dark zone. But by 12 days, their behavior was back to normal.

The fish might become more anxious because of changes in the function of receptors called GABAA receptors in the brain, the authors say. But whether the increased anxiety affects the fish’s survival remains to be seen. Roberta Kwok | 27 November 2013

Source: Hamilton, T.J. et al. 2013. CO2-induced ocean acidification increases anxiety in Rockfish via alteration of gamma-amminobutyric acid type A receptor functioning. Proceedings of the Royal Society B doi: 10.1098/rsbp.2013.2509.

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