The first global analysis of how marine environments react to the ever-increasing levels of CO2 that humanity is pumping into the atmosphere does not bode well at all for tomorrow’s would-be fishers. Published today in the journal Proceedings of the National Academy of Sciences (PNAS), the work of the University of Adelaide’s marine ecologists states that the warming and expected ocean acidification is likely to produce a reduction in diversity and numbers of various key species that underpin marine ecosystems around the world.

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“This ‘simplification’ of our oceans will have profound consequences for our current way of life, particularly for coastal populations and those that rely on oceans for food and trade,” says Associate Professor Ivan Nagelkerken, Australian Research Council (ARC) Future Fellow with the University’s Environment Institute.

Associate Professor Negelkerken and fellow University of Adelaide marine ecologist Professor Sean Connell went through the data from 632 published experiments focusing on waters from all types of climate and ecosystems, from tropical to arctic, and ranging from coral reefs to forests of kelp or open oceans.

“We know relatively little about how climate change will affect the marine environment,” says Professor Connell. “Until now, there has been almost total reliance on qualitative reviews and perspectives of potential global change. Where quantitative assessments exist, they typically focus on single stressors, single ecosystems or single species.

“This analysis combines the results of all these experiments to study the combined effects of multiple stressors on whole communities, including species interactions and different measures of responses to climate change.”

The researchers found that there would be “limited scope” for acclimation to warmer waters and acidification. There aren’t that many species that can escape or adapt fast enough to keep pace with the effects of increasing CO2 levels, and the researchers expect a large reduction in both species diversity and abundance across the globe. Interestingly enough, not all species will feel the blow — microorganisms are actually expected to increase in number and diversify.

We will feel the effects too — even if primary production (plankton) is expected to increase in the warmer waters, it’s doubtful that this will translate into secondary production (zooplankton and smaller fish) due to the more acidic environment, so the amount of food we can pull out of the ocean will be dramatically reduced.

“With higher metabolic rates in the warmer water, and therefore a greater demand for food, there is a mismatch with less food available for carnivores—the bigger fish that fisheries industries are based around,” says Associate Professor Nagelkerken. “There will be a species collapse from the top of the food chain down.”

The analysis also showed that with warmer waters or increased acidification or both, there would be deleterious impacts on habitat-forming species — coral, oysters and mussels for example. Any slight change in the health of habitats would have a broad impact on a wide range of species these reefs house.

Another alarming finding was that acidification would lead to a decline in dimethylsulfide gas (DMS) production by ocean plankton which helps cloud formation and therefore in controlling the Earth’s heat exchange.