'No escape' as invisible ocean killer spreads across planet

Ocean acidification will change the entire structure of the world's reefs, leaving fish nowhere to escape.

A red circle around carbon dioxide bubbling up from underwater vents off Papua New Guinea.
Carbon dioxide bubbles up from underwater vents off Papua New Guinea. Source: Ivan Nagelkerken

Fish will have nowhere to flee and nowhere to hide as an invisible force steadily alters the world’s oceans. What’s causing the problem is increasing water acidity, a phenomenon triggered by increased absorption of carbon dioxide from the atmosphere.

While the issue is not yet dire, by the end of the century it will be. To understand what’s in store, a leading Australian marine ecologist travelled to a remote Papuan New Guinean coral reef to study its unique conditions.

University of Adelaide’s Professor Ivan Nagelkerken donned his wetsuit and diving gear and set up cameras around an underwater volcano system that naturally spews carbon dioxide into the ocean. This environment gives an insight to how the world’s oceans could look in 75 years if the burning of fossil fuels is not stopped.

“Those areas are extremely useful as what we call natural laboratories,” Nagelkerken told Yahoo News.

“What happens is the CO2 comes from the ocean beds and dissolves in the water, acidifying it. It's exactly the same process as happens with human carbon dioxide emissions.”

Related: Popular restaurant fish set to disappear from menus

Rows of grouper being dished up at a restaurant kitchen.
Wild varieties of fish that are commonly eaten could disappear from menus if ocean acidification worsens. Source: Getty

Around 30 per cent of the carbon dioxide in the atmosphere is absorbed by the ocean, and this changes the pH. In some reef landscapes it kills off coral, while in others it alters its appearance, with the structures becoming less branched and less appealing as habitat to many fish species.

“Structure provides critical habitat for almost all species on Earth. If you don't have structure, you don't see any animals,” Nagelkerken said.

“Look at a grassy lawn and compare it to a forest. Why don't you see many species on a lawn? There's very little diversity in your habitat, and there's hardly any habitat. It's a very simple concept.

“If under future conditions our diversity of habitats decreases, and they become less complex, making them flatter with fewer shelter holes, you will find that the whole animal community, not only fish will decrease.”

University of Adelaide’s Professor Ivan Nagelkerken (pictured) set up cameras underwater to study how increased carbon dioxide impacts fish. Source: Ivan Nagelkerken
University of Adelaide’s Professor Ivan Nagelkerken (pictured) set up cameras underwater to study how increased carbon dioxide impacts fish. Source: Ivan Nagelkerken

The study began in 2019 and was published in the Journal of Animal Ecology this week. It focused on five types of damselfish and examined how they could be impacted by habitat change caused by ocean acidification.

If the problem continues to worsen, species including those targeted by recreational and commercial anglers could be killed off.

Because the problem affects the entire ocean, it could reshuffle ecological communities across the planet. Not all fish species will be severely impacted as they will be able to adapt, but others will not survive.

“It's different from ocean warming, where for example, if the tropics get warm fish can slowly move to higher latitudes where the waters are still a bit cooler,” Nagelkerken said.

“As the whole ocean acidifies there's nowhere for them to flee to. There is no escape. Some fish will simply disappear. Others will show very reduced populations in a future ocean."

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