A new study suggests that although algae is known to absorb CO2, it also emits methane – a more potent greenhouse gas (GHG).
The study, published in Nature Communications, was co-led by Christoph Humborg, scientific director of Stockholm University Baltic Sea Centre and focused on bladderwrack forests.
Coastal ecosystems are known to draw in and store vast quantities of CO2 from the air (often referred to as blue carbon), thus acting as large carbon sinks.
As such, there is much effort focused on restoring these ecosystems in various parts of the world, as a natural means of combating global warming.
Algae is considered to be a particularly potent carbon sink and is, therefore, even viewed as a one of the key blue carbon ecosystems globally.
However, the team of scientists discovered that these algae create pockets of sediment where microorganisms that produce methane can be found.
The same microorganisms, called archaea, were also found on floating filamentous algae, as well as on organic matter associated with dense populations of bladderwrack.
According to the study, the significant carbon uptake of bladderwrack forests was confirmed and estimated to be roughly 0.52 tons CO2 per hectare per year.
However, the methane emissions offset some of this uptake and the scientists calculated the net carbon uptake to be reduced to 0.38 tons of CO2 equivalent per hectare and year.
Thus, as the importance of blue carbon and awareness of the role of marine habitats in mitigating the climate crisis increase, it is just as imperative that we consider the bigger picture and take into account the fluxes of GHG.
“Caring for and restoring macroalgae habitats could still be important from a climate perspective. Our study shows that these environments are net carbon sinks, just not as large as has sometimes been suggested”, Christoph Humborg said.