Brown algae absorb large quantities of carbon dioxide from the air and release parts of the carbon they contain back into the environment in the form of a slime that is difficult to break down. Because this slime is hardly tasty to marine life, this carbon disappears from the atmosphere for a long time.
This is shown in a study by researchers at the Max Planck Institute for Marine Microbiology in Bremen (Germany). The researchers show that the algal slime called fucoidan in particular is responsible for this and estimate that brown algae could thus remove up to 550 million tons of carbon dioxide from the air each year - almost the amount of Germany's total annual greenhouse gas emissions.
Brown algae are true super plants when it comes to absorbing carbon dioxide from the air. They even outperform forests on land in this respect and therefore play a crucial role for the atmosphere and our climate. But what happens to the carbon dioxide after the algae have absorbed it? Now, researchers from the Max Planck Institute for Marine Microbiology report in the Proceedings of the U.S. National Academy of Sciences (PNAS) that brown algae can remove large amounts of carbon dioxide from the global cycle over the long term and thus counteract global warming.
Fucoidan: few like brown algae slime
Algae absorb carbon dioxide from the air and use the carbon it contains to grow. They release up to a third of the carbon they absorb back into the seawater, for example in the form of sugary excretions. Depending on how these excretions are structured, 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," says first author Hagen Buck-Wiese of the Max Planck Institute for Marine Microbiology in Bremen. "However, we have succeeded in developing a method to analyze them in detail." The researchers took a close look at a variety of different substances. The so-called fucoidan turned out to be particularly exciting. "Fucoidan made up about half of the excretions of the brown algae species we studied called bladderwrack," Buck-Wiese said. In addition, fucoidan is highly recalcitrant. "Fucoidan is so complex that it is difficult for other organisms to use. No one seems to like it." As a result, the carbon in fucoidan does not re-enter the atmosphere as quickly. "This makes brown algae particularly good helpers in removing carbon dioxide from the atmosphere over the long term - for hundreds to thousands of years."
Brown algae could sequester nearly all of Germany's carbon dioxide emissions
Brown algae are exceptionally productive. It is estimated that they absorb about 1 gigaton (one billion tons) of carbon from the air each year. If we now calculate with the results of the present study, we find that this means that up to 0.15 gigatons of carbon, equivalent to 0.55 gigatons of carbon dioxide, are sequestered by brown algae each year over the long term. By comparison, Germany's annual greenhouse gas emissions currently amount to about 0.75 gigatons of carbon dioxide, according to the Federal Environment Agency (estimate for 2020).
"What makes it even better: There are no nutrients such as nitrogen in the fucoidan," Buck-Wiese further explains. So the growth of the brown algae is not affected by the carbon losses.
Other species and locations
For the current study, Buck-Wiese and his colleagues from the MARUM MPG Bridge Group Marine Glycobiology, which is based at both the Max Planck Institute in Bremen and MARUM - Center for Marine Environmental Sciences at the University of Bremen, were able to conduct their experiments at the Tvärminne Zoological Station in southern Finland. "Next, we want to see what it looks like with other brown algae species and at other sites," Buck-Wiese says. "The great potential of brown algae for climate protection definitely needs to be further explored and exploited."
Even the plants themselves act as a crucial barrier against catastrophic climate change. Wetland ecosystems have a number of traits that lessen some of the effects of climate change, such as slowing water flow, which permits the deposition of pollutants in the wetlands and lowers erosion. With the investigation of scientific teams like in this example and the creation of a global society – network, solutions can be found and Sustainable Development Goals can be achieved faster.