Japan’s marine life could see “unprecedented changes” if carbon dioxide emissions keep increasing, a team of British, Japanese and Italian scientists warned in a recently published study.

The academics have been studying the effects of higher CO2 levels in the atmosphere upon marine fauna and flora and surveyed waters around some of Japan’s underwater volcanic vents as a “window to the future.”

Their findings show rising CO2 emissions in the atmosphere have reduced the ocean’s alkalinity (a process more commonly known as “acidification”) and harmed biodiversity. In the long run, this could have a negative effect on Japan’s prized coral and kelp forests, the scientists warn in their peer-reviewed paper.

Explaining the research, Jason Hall-Spencer, professor of marine biology at Plymouth University, said, “Unless we get a grip on reducing CO2 emissions, we will undoubtedly see major degradation of coastal systems worldwide.”

Divers from the universities of Plymouth in Britain, Tsukuba in Ibaraki Prefecture and Palermo in Italy studied reefs off Shikine Island, in the Izu Island chain south of Shimoda, Shizuoka Prefecture, which is in a transition zone between the subtropical and temperate zones.

Underwater volcanic vents pump large quantities of CO2 into the water, which reduces levels of carbonate used by organisms such as coral and shellfish to build skeletons and shells.

Scientists found that around the vents the seascape was virtually barren and dominated by small algae. As the diversity of algae and organisms declines, so does the diversity of fish higher up the food chain.

By contrast, when the divers explored areas away from the vents, which had seawater CO2 levels at pre-Industrial Revolution levels, they found an impressive amount of coral and shellfish, such as oysters, forming a diverse habitat for a wide variety of colorful marine life.

In areas that had average levels of CO2, there was far less coral and other calcified life, the study showed. The findings are worrying because the seas are predicted to “acidify” in the coming decades due to increased atmospheric CO2.

Oceans are already suffering from the effects of gradual warming — another consequence of global warming — and this has resulted in coral dying in southern Japan and warm waters have also impacted upon the growth of kelp.

In statements released to the media, various team members expanded upon the importance of their findings.

Sylvain Agostini, from the University of Tsukuba, said, “There was a mass mortality of corals in the south of Japan last year, but many people cling to the hope that corals will be able to spread north. It is extremely worrying to find tropical corals are so vulnerable to increases in CO2; this will stop them from being able to spread further north and escape the damage caused by water that is too hot for them.”

Shigeki Wada, a seaweed specialist from the University of Tsukuba, said, “When we started this work I had hoped that extra CO2 in the water would help seaweed to thrive, but we found that whilst a few species do, it is the small inedible ones that seem to do the best.”

“These are undesirable as they blanket the seabed, choking corals and lowering overall marine diversity. We know that wonderful kelp forests are dying as the waters of Japan are getting warmer, and it is now clear that extra CO2 in the water will not help them fight the stress caused by heat waves.”

One researcher suggested a silver lining.

“We are pleased to report that the currents flowing past Japan bring waters that have naturally low levels of CO2 and that fish benefit from the array of calcified habitats around our islands,” said Kazuo Inaba, who worked on the project when he was director of Shimoda Marine Research Center, part of the University of Tsukuba.

“Small further increases in CO2 do not cause major damage to the ecosystem, so if we are able to meet the Paris Agreement targets (to keep temperature rises this century well below 2 C above preindustrial levels) to limit emissions we should avoid the much higher levels of damage seen close to underwater CO2 seeps.”

The scientists’ report was recently published by Nature in Scientific Reports.

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