Rising CO2 concentrations making fish 'drunk and disorientated'

Rising carbon dioxide concentrations in seawater are set to make fish drunk and disorientated, researchers have warned. Experts from the University of New South Wales say fish could become intoxicated from the increase in CO2 decades earlier than previously thought, and that this has the potential to have "massive implications for global fisheries and marine ecosystems across the planet".

Why does CO2 make fish "drunk"? The phenomenon that causes fish to become intoxicated from high concentrations of CO2 is known as hypercapnia. The CO2 affects their brains and they lose their sense of direction and ability to find their way home – they are effectively lost at sea. Further to this, it makes them unaware of predators.

The study, published in the journal Nature in January, analysed the impact of rising CO2 emissions from fossil fuels on the natural variations in concentrations of carbon dioxide in the oceans. They used a global database of seawater CO2 concentrations collected over the past 30 years from various oceanographic programmes.

Tristan Sasse, one of the study authors, said: "We then devised a numerical method to work out the natural monthly peaks and troughs in carbon dioxide concentrations during the year across the surface of the world's oceans, based on these observations.

"This allowed us to predict for the first time that these natural oscillations will be amplified by up to tenfold in some regions of the ocean by the end of the century, if atmospheric carbon dioxide concentrations continue to rise."

Hypercapnia occurs when atmospheric CO2 concentrations exceed 650 parts per million. Their results showed that – in a high-concentration scenario determined by the IPCC – by the end of the century, half of the world's surface oceans will be affected by hypercapnia.

They wrote: "Future hypercapnia and its impact on the ocean will therefore need to be explored under a range of emission scenarios ... Many marine organisms have naturally evolved to be resilient to large fluctuations in CO2 conditions in coastal environments. Marine organisms within the open ocean, however, are not accustomed to extreme fluctuations in CO2."

Lead author Ben McNeil added: "Our results were staggering and have massive implications for global fisheries and marine ecosystems across the planet. We've shown that if atmospheric carbon dioxide pollution continues to rise, fish and other marine creatures in CO2 hotpots in the Southern, Pacific and North Atlantic oceans will experience episodes of hypercapnia by the middle of this century – much sooner than had been predicted, and with more damaging effects than thought."