They’re smaller than dust, but crucial for Earth’s climate
ZAGREB, October 10, 2025 – Coccolithophores, the microscopic planktonic architects of Earth’s climate, are finally getting the recognition they deserve. A consortium of leading European scientific institutions has united to establish October 10 as International Coccolithophore Day, aiming to spotlight their vital contributions to carbon regulation, oxygen production, and the health of marine ecosystems.
Smaller than a grain of dust and shaped like minute, intricate discs, these single-celled algae float in the sunlit layers of the ocean. They are coated with calcium carbonate plates called coccoliths and, despite their size, wield a planetary-scale influence.
A Delicate Balance Under Threat
Few people are aware of coccolithophores, yet without them, the planet's oceans and climate would look drastically different. They are among Earth's most effective natural carbon regulators, generating over 1.5 billion tonnes of calcium carbonate annually. This process captures carbon dioxide from the atmosphere and transports it to deep-sea sediments, where it can be locked away for millennia.
However, climate change is altering the temperature, chemistry, and nutrient makeup of seawater, posing serious risks to their survival and the stability of the ecosystems that depend on them.
Why Coccolithophores? The Dual Role
"What makes coccolithophores stand out is both their role in the global carbon cycle and the unique record they leave behind," says Professor Alex Poulton of the Lyell Centre. "Unlike other plankton, they build intricate calcium carbonate plates that not only help draw down CO₂ but also transport it into deep ocean sediments. This biomineralization leaves behind an exceptional geological record, allowing us to study past climate shifts."
Dr. Jelena Godrijan of the Ruđer Bošković Institute adds, "They are the ocean's invisible architects. By studying their past and current responses to ocean changes, we can better understand marine ecosystems and explore how natural processes might help us tackle climate change."
Cutting-Edge Science Across Europe
The initiative highlights groundbreaking research from several institutions:
The Lyell Centre (Scotland): The OceanCANDY team studies how these plankton pull CO₂ from the air and models how warmer, more acidic oceans could alter this process.
NORCE (Norway): Scientists like Dr. Kyle Mayers track coccolithophore life cycles, including their interactions with viruses and grazers, to show how carbon moves through the ocean. "These links shape food webs and how the ocean stores carbon," says Dr. Mayers.
Ruđer Bošković Institute (Croatia): The Cocco team investigates bacterial interactions that influence seawater chemistry and CO₂ uptake. "Their interactions with bacteria determine how carbon moves and transforms," notes Dr. Godrijan.
MARE, University of Lisbon (Portugal): Dr. Catarina V. Guerreiro leads studies on how aerosols fertilize the ocean and shape coccolithophore distribution, connecting "tiny chalky organisms to planetary carbon flows."
International Nannoplankton Association (INA): INA scientists connect living coccolithophores to their fossil record, using their microscopic plates to date rocks and trace Earth's climate history.
Why Coccolithophore Day Matters
"This could contribute to changing the way we see the ocean," says Dr. Sarah Cryer from the CHALKY project. "We most often talk about whales and coral reefs, but coccolithophores are a vital part of the planet's climate system. They remind us that the smallest organisms can have the biggest impact."
The campaign to establish International Coccolithophore Day is a call to action. By highlighting the profound role of these microscopic organisms, scientists aim to inspire a new wave of ocean literacy, policy focus, and public engagement, underscoring that the future of our climate is intimately linked to the health of the smallest ocean dwellers.