Blue carbon: seaweed

Blue carbon: seaweed

(Image: Shane Stagner)

Blue carbon : seaweed


  • Fed by the sun, some species can grow up to 1m/day, pulling up to five times more carbon dioxide from the atmosphere than rainforests, and permanently sequestering it:

“All you need to do is cut that seaweed off, and it drifts into the ocean abyss. Once it’s down a kilometre the carbon in that seaweed is effectively out of the atmospheric system for centuries or millennia. But if you plant the forest you’ve got to worry about forest fires, bugs, etc etc releasing that that carbon.” – Prof. Tim Flannery (Video 1).

“Seaweed cultivation is the world’s fastest growing aquaculture sector, with the global seaweed industry worth more than US$6bn per year. There are many species that have the potential to be transformed into a range of commercial products as well offering environmental benefits to counteract climate change.” – Cawthron Chief Executive Prof. Charles Eason

Video 1: Prof. Tim Flannery explains the incredible role that seaweed can play in drawing down carbon emissions

Ocean permaculture

The advantages of growing seaweed vs land-based crops:

  • Don’t need fresh water
  • Don’t need agrichemicals to grow
  • Don’t need pesticides
  • Doesn’t burn down
  • Doesn’t use land
  • Has more iron than meat
  • May serve as a protective nursery for organisms particularly vulnerable to acidification, such as oysters and mussels.

“Seaweeds are able to modify the chemical environment at their surface, in a micro‐zone called the diffusive boundary layer (DBL), via their metabolic processes controlled by light intensity. Depending on the thickness of the DBL, sessile invertebrates such as calcifying bryozoans or tube‐forming polychaetes living on the surface of the blades can be affected by the chemical variations occurring in this microlayer. Especially in the context of ocean acidification (OA), these microhabitats might be considered as a refuge from lower pH, because during the day photosynthesis temporarily raises the pH to values higher than in the mainstream seawater ” – Noisette & Hurd, University of Tasmania

Reduces methane from ruminant animals (cows, sheep)

Considerable research is ongoing in this sector. When fed certain species of seaweed, the amount of methane that cows produce through enteric fermention (digestion followed by burps) is considerably reduced. At first glance, this seems like a game-changer, particularly for the New Zealand  dairy sector. However, it’s not quite that simple.

Research by the University of California and CSIRO (Australia) shows that Holstein dairy cows fed Asparagopsis armata (the species native to New Zealand) results in less methane being produced, but with some caveats. Cows given higher doses produced up to 66% less methane but they also ate less, gained less weight, produced more than 10% less milk, and the quantity of protein in the milk fell. They also produced more carbon dioxide and bromoform (which damages the ozone layer in the upper atmsosphere) than the control subjects. While smaller doses reduced these side effects, the drop in methane emissions wasn’t nearly as impressive.

“The other major obstacle to using seaweed inhibitors on New Zealand farms is the fact our sheep, beef cattle and dairy cows mostly eat grass. That makes feeding a supplement a potential logistical nightmare. In trials, the seaweed is mixed with a dry food ration. That’s fine for intensively farmed animals fed grain-based diets. But how do you feed it to a sheep grazing on the far flanks of a high country sheep station?” Stuff, 2020

While seaweed may not be a magic bullet, it offers a luring promise for the agricultural sector if an optimal dosage and accurate delivery system can be developed. Thanks to $6m of funding from the Government’s Provincial Growth Fund, the Cawthron Institute is expanding its algae research.

Wild harvest may help improve biodiversity

The seaweed species known as wakame (Undaria pinnatifida) is one of the 100 most invasive species worldwide. Unfortunately, it invaded New Zealand waters in the 1980s and eradication programmes have failed. Known as ‘the gorse of the seas’, it’s now commonly found around our coastline, displacing native species.

In a joint Singapore-New Zealand government project and funding from the New Zealand Catalyst Fund, AgResearch is looking at ways to make the proteins in seaweed more digestible and the nutrients locked up in the plant, more accessible. One of the aims is to increase interest in wild harvest of the seaweed from infested coastlines, which might also encourage native seaweed species to re-establish.

Fig 1. Wakame : Undaria pinnatifida (Image: Wikipedia commons)
Fig 1. Wakame : Undaria pinnatifida (Image: Wikipedia commons)


Video 2: What is blue carbon?


To draw excess greenhouse gasses, primarily carbon dioxide from the atmosphere and store it back underground. See the carbon cycle.