Solving climate mysteries with corals

Corals are animals that live in shallow tropical waters. They spawn around the time of a full moon, and the larvae attach themselves to the seabed and start building a skeleton made of calcium. Then they divide and spread out as a colony, eventually forming a coral reef. The reefs can exist for thousands of years, even after the coral has died.

Corals have a symbiotic relationship with algae called zooxanthellae. The algae produce food through photosynthesis, and the coral provides the algae with shelter. Excess nutrients, expelled as mucus, attract microorganisms and the fish and shellfish that prey on them, building a rich ecosystem around a coral reef. Over time, corals become deeply engraved with the history of the global environment and human civilisations.

Turning back time

Tsuyoshi Watanabe, a Senior Lecturer at Hokkaido University’s Faculty of Science, specialises in coral dating and climate change research. He and his team slice coral skeletons into thin sections and then study the coral’s annual rings, which are similar to the growth rings of trees. Samples from each ring are then ground into a fine powder and dissolved in acid to produce carbon dioxide. The team measures the isotope ratios of oxygen and carbon to get an idea of the environment the coral lived in, such as water temperature and precipitation levels. Combining this data with historical records can tell us about how people lived in particular periods.

For example, in 2019 Watanabe’s team published a study about the fall of the Akkadian Empire, which was founded in Mesopotamia about 4,600 years ago. The Akkadian Empire flourished for about 400 years, but then collapsed suddenly. It was located in a prosperous agricultural region, but coral data revealed that there was a time when dry winter winds blew continuously for up to three months. The prolonged dryness may have made the area uninhabitable, leading to the empire’s demise.

Hearts and minds

Watanabe and his team repurposed a closed primary school on Kikai Island in Japan to create the KIKAI Institute for Coral Reef Sciences in 2015. In collaboration with local communities, the team has also used theatre to spread information and teach people about corals. Kikai is a coral reef island, and for generations the inhabitants have lived off fish from the reefs, built walls and tombs from coral, and developed songs and dances about harmony with the coral ecosystem.

“I realised that we should interpret the data not just as a prediction of the future but also of whether people’s hearts and minds will follow this vision of society. It’s important to think together about what kind of future we would like to achieve or accept. Through theatre, we can reach deeper into the minds of the people in the past and what kind of future the people here identify with,” explains Watanabe. He’s been approached to build coral research and education centres on other islands as well. “I feel that what’s happening here is a good cycle for both the researchers and the people.”

Following in coral’s footsteps

Corals span space and time, from the fleeting to the immense. The larvae are just a few millimetres, free-floating for about a week before attaching to the seabed, but large reefs can be thousands of kilometres in size and exist for thousands of years. “Since the Industrial Revolution, people have been burning fossil fuels and changing the planet’s climate. Corals have adapted to changes in the past, but if human-induced climate change happens faster than corals can adapt, then we’ll have a tough future ahead of us,” laments Watanabe.

Further information

Dr Tsuyoshi Watanabe 
[email protected] 
Hokkaido University

Hokkaido University inquiries 
Public Relations & Communications Division 
[email protected]  

More Asia Research News 2025 stories

Book your space for 2026