Brown algae absorb half a billion tons of CO2 each year

Brown algae could remove up to half a billion tons of carbon dioxide from the atmosphere each year, storing it in the form of slime, according to a new study led by the Max Planck Institute for Marine Microbiology. The slimy mucus, known as fucoidan, is extremely hard to break down, which means that the carbon is securely stored for a long time. 

“Fucoidan made up about half of the excretions of the brown algae species we studied, the so-called bladderwrack,” explained study first author Hagen Buck-Wiese.“The fucoidan is so complex that it is very hard for other organisms to use it. No one seems to like it.” 

“This makes the brown algae particularly good helpers in removing carbon dioxide from the atmosphere in the long term – for hundreds to thousands of years.”

Once the algae absorb atmospheric carbon dioxide, up to a third of this carbon is released back into the ocean through sugary excretions. These excrements are either used by other organisms or sink to the bottom of the ocean. 

“The excretions of brown algae are very complex and therefore incredibly complicated to measure,” said Buck-Wiese. “However, we have managed to develop a method to analyze them in detail.” 

The researchers used this technique to examine many different substances, including fucoidan. The experts found that, on an annual basis, brown algae sequester the equivalent of 0.55 gigatons of carbon dioxide. To put this into perspective, carbon dioxide emissions from Germany reach about 0.74 gigatons per year. 

“And even better: The fucoidan does not contain any nutrients such as nitrogen,” explained Buck-Wiese. This means that the carbon losses do not affect the growth of brown algae. 

“Next we want to look into other brown algae species and other locations,” said Buck-Wiese. “The great potential of brown algae for climate protection definitely needs to be further researched and utilized.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Editor

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