By Hiroshi Masumitsu / Yomiuri Shimbun Senior Writer

Does the chemical reaction that builds seashells and coral skeletons really increase the amount of carbon dioxide in the atmosphere? A project to tackle this major theme related to global warming began this spring in Japan.

It is widely accepted that the reaction to form calcium carbonate -- the main component of seashells and coral skeletons -- in seawater leads to an increase in atmospheric CO2. However, recent findings suggest that a different chemical reaction occurs inside organisms that may not release CO2.

If this reaction, which has been considered as a CO2 source, is found to be a sink instead, then shellfish farming and coral conservation could gain new value as contributors toward preventing global warming. It may also increase Japan's overall CO2 absorption. "Expectations from the industry are very high," said Michio Suzuki, a professor at the University of Tokyo who specializes in bioinorganic chemistry. Suzuki serves as the leader of the project.

CO2 is locked within calcium carbonate (CaCO3), which forms structures such as seashells. On the other hand, established theories suggest that when calcium carbonate is created in the ocean, it also leads to the release of CO2 dissolved in seawater, ultimately contributing to an increase in atmospheric CO2.

Ko Yasumoto, an associate professor at Kitasato University, and his coresearchers examined the larvae of a coral species called Koyubimidoriishi. They discovered that the extracellular calcifying medium (ECM) of the larvae that forms its skeleton has a higher hydrogen ion index (pH) than seawater, meaning it is more alkaline.

The reaction to form calcium carbonate varies with pH. If it occurs in seawater, which has a pH of 8.1, CO2 will be released. However, the pH of ECMs ranges from 8.5 to 9.0. It is believed that CO2 will not be emitted at such high pH levels.

Based on such findings, the new project will verify the truth of established theories. The project aims to uncover details about the reactions occurring within shellfish and coral bodies and will conduct rearing experiments to measure the release of CO2. More than 20 researchers from universities and research institutions, including Yasumoto, will take part in the project. The project was chosen by the Education, Culture, Sports, Science and Technology Ministry to receive a subsidy.

When seaweed and seagrass that absorb CO2 through photosynthesis sink and accumulate on the seafloor, they can be counted toward a country's total CO2 absorption as "blue carbon." It is estimated that 190 million tons of CO2 are absorbed annually in this manner.

Meanwhile, Yasumoto believes that the amount of CO2 incorporated by marine organisms, such as shellfish, in their calcium carbonate skeletons is much larger, estimating it to be around 530-800 million tons annually. Yasumoto calls it "neo-blue carbon," and says that he is eager to clarify its true nature.

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This article is from The Yomiuri Shimbun. Neither Dow Jones Newswires, MarketWatch, Barron's nor The Wall Street Journal were involved in the creation of this content.

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October 16, 2025 03:54 ET (07:54 GMT)

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