Status: 02/08/2023 10:42 a.m
Not only forests on land can be a sink for carbon. A special algal slime could also help sink a significant amount of carbon into the sea floor.
Dark brown with a greenish tinge, it grows near the shore or lies washed up on the beach – the bladderwrack. It also occurs frequently on the German North and Baltic Seas. In some people, it also causes discomfort or even disgust because of its consistency. The algae not only provide an important habitat for many animals.
A new study by researchers at the Max Planck Institute for Marine Microbiology in Bremen found that Fucus vesiculosusas it is scientifically named, could also play an important role in the climate crisis – through its slime.
Slime binds carbon
Fucoidan – that’s the name of the slimy substance that could help mitigate the climate crisis. The substance is formed in particular by brown algae. Also from the eponymous bladder wrack Fucus. It actually supports the algae from the inside. However, it also binds carbon in the seabed in the long term.
Because not only the bladderwrack, but all algae and plants in general, store carbon during photosynthesis and convert it into biomass. Also from carbon that has entered the sea as CO2 from the atmosphere. Normally, when the plants die, bacteria decompose this biomass. The bound carbon is released again at the end of the plants lifespan.
Bacteria hate mucus
During their lifetime, brown algae secrete a lot of mucus in the form of long-chain sugars, so-called polysaccharides. According to the new study, almost half of these in bladderwrack are fucoidan. That could be good news for the climate, says Jan-Hendrik Hehemann, one of the authors: “Because fucoidan also contains a lot of carbon and is poorly broken down by bacteria, it could be a good carbon sink.”
The fact that fucoidan is rejected by the bacteria and can therefore bind carbon from the atmosphere for a long time can also be seen on the sea floor. Because even deep in the ground, where the sand and everything that surrounds it is hundreds of years old, just as much of the algae slime Fucoidan can be detected as directly on the surface. The fucoidan here could already be more than 1000 years old and thus store carbon for a very long time and thus remove it from the atmosphere.
Relevant carbon sink
It is very likely that other brown algae, which are even more abundant than bladderwrack, are also high in fucoidan. Hagen Buck-Wiese now wants to investigate exactly how much and how much carbon the algae can remove from the atmosphere in the long term through their slime. He is the first author of the study and has developed a novel method for measuring the amount of fucoidan.
If the amounts of other brown algae are as high as in bubble day, then algae would be a relevant carbon sink, he says: “If you extrapolate it, that would mean that maybe half a gigatonne of fucoidan a year ends up in the sea and carbon saves.”
snow in the sea
Florian Weinberger, who researches algae at the Geomar Helmholtz Center for Ocean Research in Kiel and is not involved in the study, also thinks this is quite possible. Especially when the algae slime gets deep – for example over so-called sea snow.
Sea snow, or English “marine snow”, refers to flakes that form near the sea surface. They consist, for example, of the long-chain sugars that are released as mucus by larger algae and of dead, microscopic algae. The flakes sink slowly and get into deeper water layers where there is no more oxygen. “You can then assume that their degradation will slow down a lot there,” says Weinberger. This is because the bacteria are no longer particularly active here.
Reforest algal forests
For a long time there have been calls reforest algal forests, also to mitigate climate change. The new study shows that the algae do not need to be sunk at all in order to remove carbon from the system in the long term. It could also be enough to let them grow at all.
Hehemann advocates economic incentives. “Theoretically, an algae farmer could perhaps be paid twice. Once for the time that the algae lives and binds carbon and then also for the product that is sold to people,” he says.