Science and technology - Aquaculture: Seaweed at scale
Floating offshore farms should increase production of a useful crop, and might even help alleviate climate change
IN MANY PLACES where seaweed used to thrive, often growing in vast “forests”, it is disappearing.
The cause is global warming, which, by heating the ocean’s upper layer, reduces its density through thermal expansion—thus making it more buoyant.
That extra buoyancy means it is less likely to mix with cooler, denser and more nutrient-rich waters below.
This is bad for the marine environment in general.
More specifically, it is bad for commercial seaweed farming, a business with revenues of (depending on whom you ask) between $6bn and $40bn a year.
The algae involved, particularly kelp, are popular in Asian cuisine.
They are also used as fertiliser, and are processed into carrageenan, a natural binder and emulsifier employed in foods, cosmetics and drugs.
Most are grown either on the seabed or on ropes attached to it. But some are cultivated on small floating platforms.
To counter the effects of surface heating, which are particularly pronounced in the tropics, researchers are trying to improve the floating-platform approach by assisting the upwelling of cooler waters to stimulate algal growth on such platforms.
This would also increase the area available for seaweed farms, by allowing them to be located well away from coastlines.
An experimental floating farm installed in August, off the coast of the Philippines, by a group led by the Climate Foundation, an American charity, is one of the largest attempts so far to do this.
Artificial stimulation of upwelling is not a new idea.
It has been touted for years as a way to regenerate kelp forests, in particular. And for good reason.
With enough nutrients, fronds of giant kelp, which grow to an average length of about 30 metres, can elongate by more than 50cm a day.
Only now, however, is upwelling-stimulation being attempted seriously.
The foundation’s test platform has an area of 100 square metres.
It employs solar-powered turbines to suck water up from a depth of several hundred metres through flexible, cylindrical pipes.
The foundation plans to experiment with wind-powered and wave-powered turbines, too.
If this works, which early results suggest it does, and can be scaled up, not only could such technology boost seaweed production, it might also help ecosystems that depend on seaweed forests.
And—at least in theory—if part of the harvest were sacrificed by sinking it into the deep ocean, that might act as a novel form of carbon capture and storage which could help slow the warming that caused the problem in the first place.
According to Brian von Herzen, who runs the foundation, the organisation carried out smaller-scale experiments, using similar technology, in 2020.
該基金會的負責人布萊恩·馮·赫爾岑(Brian von Herzen)表示，該組織在2020年使用類似的技術進行了小規模的實驗。
These showed that seaweed grows four times faster on platforms irrigated with upwelled water than on equivalent, unirrigated platforms.
Moreover, it continues to grow during the warmest months of the year, when seaweed not so irrigated actually shrinks.
Dr von Herzen and his colleagues hope to use experience gathered from their latest rig to develop a platform that would cover an entire hectare of the ocean’s surface—100 times the area of the one just launched.
To that end, they are collaborating with the Marine Bioproducts Cooperative Research Centre, a public-private partnership in Australia.
At this scale, the partners estimate, a seaweed farm could pay for itself within five years.