Fish Struggle to Adapt to Rising Carbon Dioxide Levels in Ocean

Research into the way that fish cope with rising carbon dioxide levels in oceans has found that they adversely change the behaviours of fish though generations. This poses the possibility that marine species may never fully adapt to their changed environment.

The study looked at spiny damselfish, which were kept in water with different CO2 levels for several months. One set was consistent with if the world were to take rapid action to cut carbon emissions, while the other reflects the current trend in rising carbon emissions.

The offspring of the damselfish were also kept in the same conditions as their parents. The researchers found that the juveniles of fish from the high CO2 water were no better than their parents at coping with the conditions.

These findings suggest that fish will take several generations to adapt to the changing environment, with no guarantee that they will ever do so.

The study was conducted by the ARC centre of excellence for coral reef studies, based at James Cook University in Queensland, and was published in Nature Climate Change.

Previous studies at the centre found that rising CO2 levels in the oceans directly affects fishes’ brains, modifying their behaviour. Their sense of smell and their wariness is hindered, making them more likely to be killed by predators.

Why are the CO2 Levels in the Oceans Changing?

More than 90% of the excess CO2 in the atmosphere, which is caused by the burning of fossil fuels, is soaked up by the ocean. When CO2 is dissolved in water it causes acidification, which lowers the pH of the water. In highly acidic water, crustaceans can’t form shells and corals are prone to bleaching.

A co-author of the study told Guardian Australia, “How quickly that adaptation will take, we don’t quite know,” he said. “But we do know that projected future CO2 levels will seriously affect the behaviour of fish in ways that won’t be good for populations. It will take longer than a few generations for fish to genetically adapt and we don’t know if they can keep pace with the change.

“If they can’t keep pace, it will have a significant effect on the population sustainability in some species of fish. We worked on reef fish, but there’s nothing to say that whole ranges of other species won’t be affected.

“This is certainly a warning that there is no quick fix for fish. We need to reduce carbon dioxide emissions and we need to do more to understand whether genetic adaptation can kick in over time.”