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Blue carbon: kelp & seaweed superpowers

Blue carbon: seaweed

Image: Shane Stagner

Blue carbon : kelp & seaweed superpowers

Summary

  • Fed by the sun, some species can grow up to 1m/day, drawing down as much as 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. 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

Image: Shane Stagner

Blue carbon : kelp & seaweed superpowers

Summary

  • Fed by the sun, some species can grow up to 1m/day, drawing down as much as 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. 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

New Zealand is well suited to this Greenfield form of carbon sequestration due to the presence of submarine canyons leading to very deep water around its continental shelf. Blue Carbon contrasts sharply from carbon sequestration by traditional terrestrial forestry. Terrestrial forestry is only able to store carbon in a living form and, therefore, reaches maximum storage capacity very quickly. Furthermore, commercial plantation forestry systems become net carbon emitters after 90 to 140 years due to the emissions produced in forestry management, logging, milling and transportation. ” – Blue Carbon NZ

Permanent carbon sequestration

Seaweed is a diverse group of marine macroalgae that, like all plants, uses photosynthesis and carbon dioxide to grow. While it’s well understood that kelp stores far more carbon than trees, and it does so faster, the exact amount hasn’t been quantified so it’s not included as a ‘carbon farming’ crop under the Emissions Trading Scheme. The simple reason for this is that the forestry industry has a vested interest in claiming carbon credits. These ‘credits’ are arguably spurious as they come with huge risks and ignore the true cost of sacrificing natural ecosystem services to monculture plantations.

In New Zealand, one of Blue Carbon Services Ltd research projects in conjunction with NIWA is to quantify how much carbon is in natural kelp beds that grow along the coast, and ends up accumulating in deep-sea (continental shelf, slope, and submarine canyons) sediments. Knowing this would go a long way to creating a genuinely safe and reliable carbon market, one that does not require sacrificing ecosystems for profit, and one that may also enhance seafood production through multi-trophic aquaculture.

Integrated multi-trophic aquaculture

The advantages of growing seaweed vs land-based crops:

  • Doesn’t need fresh water
  • Doesn’t need agrichemicals to grow
  • Doesn’t need pesticides
  • Doesn’t burn down
  • Doesn’t use land
  • Has more iron than meat
  • Has more calcium than milk
  • Serves 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

Videos 2 and 3 explain how kelp is being grown as a food crop for people and animals, as a fertiliser that takes nitrogen from polluted estuaries to grow and is then returned to farms as a natural fertiliser, and how the  ‘halo’ effect of kelp reducing the acidity of surrounding waters makes it an ideal co-crop for growing shellfish, given that ocean acidification is already having a measurably bad impact on marine ecosystems. The kelp growing system can be designed to withstand storms by lowering the kelp into deeper waters when necessary.

The videos feature the work being done in the US by GreenWave. Their 3D ocean integrated multi-trophic aquaculture concept is being research and trialled in New Zealand by GreenWave and the Cawthron Institute and by Blue Carbon NZ.

Fig. 1. how growing kelp can benefit shellfish aquaculture as well as natural ecosystems (Image: The Nature Conservancy)
Video 2: Bren Smith TED talk expands Prof. Flannery’s talk, taking the concept into ocean farming.
Video 3: Follow up presentation post-Covid. This link begins around 3 minutes into the full video, explaining how carbon locked in kelp is also being harvested and sequestered into terrestrial soils for regenerative agriculture.

Reduces methane from ruminant animals (cows, sheep)

When fed certain species of seaweed, the amount of methane that cows produce through enteric fermentation (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 Cawthron Institute is expanding its algae research as it offers a luring promise for the agricultural sector if an optimal dosage and accurate delivery system can be developed. The Sustainable Seas Challenge (part of the National Science Challenge New Zealand) is undertaking a range of research projects on seaweed.

“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

There is also an argument that funding this research will only offer misplaced hope to an unsustainable ‘sunset industry’ that also produces large quantities of the greenhouse gas nitrous oxide and is badly polluting our waterways. As the price of carbon continues to climb, growing protein in this way may become prohibitively expensive.

“Methane emissions are only one way that animal agriculture contributes to environmental destruction. Animal agriculture is a major contributor to nitrous oxide emissions and feeding cows seaweed would make no difference to that. Recent advances in precision fermentation technology [protein alternatives] mean that animal agriculture will be obsolete in the next 10 years.” – China Agricultural University former lecturer in environmental management, Michael Morris (Stuff, 2020)

Wild harvest may help improve biodiversity

The seaweed species known as wakame (Undaria pinnatifida) (Fig. 2) 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. This is not likely to make a huge difference, if any, to restoring native kelps as the same strategy has been used in terms of hunting possums and other feral pests. We include it here only as a matter of interest.

Fig 2. Wakame : Undaria pinnatifida (Image: Wikipedia commons)
Fig 2. Wakame : Undaria pinnatifida (Image: Wikipedia commons)

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