When I think of seaweed, I either think of a delicious addition to a Chinese takeaway or an unsightly plant that puts my mother off of a beach sunbathing spot. Seaweed is not often thought of as a natural climate solution. In fact, seaweed ecosystems can draw down and sequester more carbon than the world’s forests or peatlands per unit area.
A recent paper from Froelich et al. found there is a potential ocean capacity of ~48 million square kilometres (six times the size of Brazil) where seaweed farms could be established. Just 0.001% of this area (approximately the size of the island of the Dominican Republic) would offset the carbon emissions of the world’s aquaculture industry.
Until recently, seaweed has been overlooked as an NCS. However, with such large carbon storage potential in relation to area, seaweed is fast-emerging, attractive natural climate solution (NCS).
Not all weeds in the sea are seaweed
There is a fundamental difference in submerged aquatic vegetation – a lot of people think plants that line seabeds in coastal ecosystems as seaweed. But, these are seagrasses as they are rooted in the seabed. Seaweed is a multi-cellular mass of macro-algae that does not require a root system – only a medium upon which it can attach a hold-fast to (Figure 1). The hold-fast acts as an anchor. This is important in terms of NCS, as it means seaweed does not necessarily require the seabed to grow. Seaweed can be farmed away from the coastline up to depths of thirty metres or more depending on water clarity and light penetration. Thus, seaweed can be farmed in addition to coastal blue carbon solutions such as mangroves and seagrass.
Figure 1 - The difference between seaweed (algae) and seagrass taken from the Smithsonian
Natural help from kelp
The image below shows how seaweed can sequester carbon in the deep ocean.
Taken from Harvard University
Kelp is a type of seaweed and can be engineered as a NCS using marine permaculture arrays (MPAs) (Video 1). Beyond carbon sequestration, these kelp farms can bring multiple ecosystem co-benefits. MPAs can help restore anoxic, ocean dead-zones to biodiverse marine ecosystems. Seaweed absorbs carbon dioxide (CO2) and neutralises ocean acidification, which can assist re-growth of nearby corals. Furthermore, the seaweed can absorb excess nutrients or toxins from coastal waters affected by agricultural run-off and eutrophication. From a climate change adaptation standpoint, seaweed can also act as a coastal defence by dissipating wave impacts.
Video 1: Taken from Land Sea Studios
From a commercial standpoint, seaweed can be harvested for consumption or used as a biofuel alternative to fossil fuels. It can also be used as a substitute in cattle feed, which reduces methane emissions from cattle farming.
Work is currently being conducted by Dr Brian von Herzen to use MPAs to tackle global food insecurity. The team are working to upscale MPAs to disseminate them globally. With trials underway in Florida, Australia and the Philippines, the project aims to provide livelihoods for communities through seaweed farming while absorbing CO2.
The seaweed challenge
As with all NCS – seaweed is not a silver bullet. At present, awareness of seaweed as a NCS is low. Furthermore, the technology to identify viable areas for farms and scale permaculture technology is in its adolescence. Finally, the demand for seaweed-based products is limited. Although, education on the commercial opportunities for fuel, food and feed could help to drive increased demand.
But, how will climate change, warming oceans and increased CO2 affect seaweed productivity? At present, little is understood. But, some research shows warmer water temperatures may affect spore production and thus, limit proliferation.
However, the effects of climate change are still relatively unknown for many NCS, including forests. This has not stopped the establishment of carbon-offset schemes encouraging forest regeneration. In the face of runaway climate change, could it be time to upscale marine NCS to support their terrestrial counterparts?
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