Ocean Acidification

Paul Bunje is senior scientist for energy and environmental programs at XPRIZE, an awards organization based in Southern California. What does Dr. Bunje do? In his own words: “I work to help solve environmental grand challenges by inspiring and facilitating innovation.” Trained as an evolutionary biologist, Dr. Bunje was founding director of the Los Angeles Regional Collaborative for Climate Action and Sustainability. At XPRIZE, Dr. Bunje is helping to lead the organization’s work on climate change. He talked to Maya Bon for Climate Resolve about ocean acidification and hypoxia, an area of focus for XPRIZE — and what we can do about these threats.

Can you give us a background on ocean acidification — what it is, how it’s caused, what it does to the ocean, and how it relate to climate change?

Paul Bunje: Ocean acidification is essentially the evil twin of climate change, as it is also the consequence of carbon dioxide emissions. About one quarter of the CO2 that we’ve emitted into the atmosphere is absorbed by the world’s oceans. When you put CO2 into water, it forms carbonic acid, which in turn drives down the pH of seawater. The challenge is that this is happening globally — as more CO2 goes into the atmosphere, more goes into the ocean…. [and] upsets the chemical balance of carbonate ions, carbonic acid, and CO2, which changes the chemistry that sea creatures work within.

One of the first identified impacts were the shells of creatures that make their shells out of calcium carbonate — corals, mollusks, bivalves, some important phytoplankton such as coccolithophore, which produces a significant amount of oxygen for the planet. When this chemistry balance is upset, it becomes more difficult to get the carbonate out of the water and these creatures cannot make their shells. In extreme cases, the shells dissolve. There are interesting cases of this occurring with sea butterflies, a microscopic snail, because of ocean acidification. You can actually see their microscopic shells dissolving in water.

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High levels of carbon dioxide could impair the brain chemistry of fish, scientists found.

Researchers from the University of Miami Rosenstiel School of Marine and Atmospheric Science and the ARC Center of Excellence for Coral Reef Studies at James Cook University found that increased concentrations of carbon dioxide in the ocean alters the brain chemistry of fish that may lead to neurological impairment.

“Coral reef fish, which play a vital role in coral reef ecosystem, are already under threat from multiple human and natural stressors,” Rachael Heuer, lead author of the study, said in a news release. “By specifically understanding how brain and blood chemistry are linked to behavioral disruptions during CO2 exposure, we can better understand not only ‘what’ may happen during future ocean acidification scenarios, but ‘why’ it happens.”

In the study published in the journal Scientific Reports, researchers collected spiny damselfish from the reefs off Lizard Island in Australia’s Great Barrier Reef. The fish were separated into two groups: one is exposed to ordinary CO2 “control conditions and the other exposed to elevated CO2 levels expected to occur by the year 2300. After the exposure, the two fish groups were subjected to a behavioral test, and brain and blood chemistry were measured.

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Tropical coral reefs lose up to two thirds of their zooplankton through ocean acidification. This is the conclusion reached by a German-Australian research team that examined two reefs with so-called carbon dioxide seeps off the coast of Papua New Guinea. At these locations volcanic carbon dioxide escapes from the seabed, lowering the water’s acidity to a level, which scientists predict for the future of the oceans. The researchers believe that the decline in zooplankton is due to the loss of suitable hiding places. It results from the changes in the coral reef community due to increasing acidification.

Instead of densely branched branching corals, robust mounding species of hard coral grow, offering the zooplankton little shelter. In a study published on 19 September 2016 at the online portal of the journal Nature Climate Change, the researchers report that the impact on the food web of the coral reefs is far-reaching, since these micro-organisms are an important food source for fish and coral.

The volcanic carbon dioxide sources off the coast of Papua New Guinea are a unique natural laboratory. “Here, we can already observe under natural conditions how the reefs may change when the world’s oceans absorb more and more carbon dioxide from the atmosphere and the acidity of their water rises due to climate change,” says coral expert and study co-author Prof Claudio Richter of the Alfred Wegener Institute, the Helmholtz Centre for Polar and Marine Research.

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