When it comes to absorbing carbon dioxide from the air, brown algae are true miracle plants. They even surpass terrestrial forests in this, and thus play a fundamental role in the atmosphere and our climate. But what happens to the carbon dioxide that the algae absorb? In the journal Proceedings of the National Academy of Sciences (PNAS), scientists from the Max Planck Institute for Marine Microbiology reveal that brown algae can remove large amounts of carbon dioxide from the global cycle over the long term, thereby counteracting global warming.
Algae take in carbon dioxide from the atmosphere and use the carbon to grow. They release up to a third of the carbon they absorb back into the seawater, for example in the form of sugar exudates. Depending on the structure of these excretions, they are either quickly used by other organisms or sink towards the seabed.
“The excretions of brown algae are very complex and therefore incredibly complicated to measure,” said first author Hagen Buck-Wiese of the Max Planck Institute for Marine Microbiology in Bremen, adding: “However, we managed to develop a method to analyze them. in detail.”
Using this method, scientists have studied a large number of different substances. The so-called fucoidan proved particularly exciting. “Fucoidan made up about half of the excretions of the species of brown algae we studied, the so-called blebs,” Buck-Wiese said.
Fucoidan is a stubborn molecule. “Fucoidan is so complex that it’s very difficult for other organisms to use it. Nobody seems to like it,” he said. As a result, carbon from fucoidan is not quickly returned to the atmosphere. “This makes brown algae particularly good helpers in removing carbon dioxide from the atmosphere over the long term – hundreds to thousands of years,” he added.
Brown algae could bind almost all of Germany’s carbon dioxide emissions
Brown algae are remarkably productive. They are estimated to absorb about 1 gigatonne (billion tonnes) of carbon per year from the air. Using the results of this study, this would mean that up to 0.15 gigatons of carbon, equivalent to 0.55 gigatons of carbon dioxide, is sequestered by brown algae each year over the long term. For comparison: According to the Federal Environment Agency (Umweltbundesamt, 2020 estimate), Germany’s annual greenhouse gas emissions currently amount to about 0.74 gigatonnes of carbon dioxide.
“And even better: Fucoidan does not contain any nutrients such as nitrogen,” explains Buck-Wiese. Thus, the growth of brown algae is not affected by carbon losses.
More species and locations
For this study, Buck-Wiese and his colleagues from the MARUM MPG Bridge Group Marine Glycobiology, which is based at both the Max Planck Institute Bremen and the MARUM – Center for Marine and Environmental Sciences at the University of Bremen, conducted their experiments at the Zoological Station Tvarminne in the southern Finland. “Next time we want to look at other species of brown algae and other places,” said Buck-Wiese, adding: “The great potential of brown algae for climate protection definitely needs to be further explored and exploited.”
