How seaweed is farmed and harvested
More than half of the world's farmed seaweed comes from China, mostly grown on lines in shallow sea.
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The short version
Seaweed farmers tie seedlings to ropes or monofilament lines and string them between stakes in shallow water, or float long-lines anchored to the bottom in water about 7 meters deep. The plants grow in the sea with little need for fertilizer or fresh water, and are cut or hauled in when mature.
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Tie seedlings to lines
In the off-bottom method seedlings are tied to monofilament lines strung between stakes driven into the shallow sea floor. The earliest Philippine guides recommended reef flats at about one meter depth at low tide.
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Float long-lines in deeper water
Long-line farms anchor floating cultivation lines to the bottom in water around 7 meters deep. Saccharina kelp, Undaria, Eucheuma, Kappaphycus and Gracilaria are all raised this way, with low technology and a lot of hand labor.
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Cut and haul the crop
Farmers take the mature seaweed from the lines. Seaweed is an extractive crop that needs little fertilizer or fresh water, so it has a smaller footprint than fed aquaculture.
Worth repeating
- Seaweed is a name for thousands of species of marine algae, in red, brown and green groups.
- Seven taxa dominate cultivation, including Eucheuma, Gracilaria and the Pyropia used for nori.
- In Japan, nori production is worth US$2 billion a year.
Where it comes from
- China58.62% of world output
- Indonesia28.6%
- South Korea5.09%
- Philippines4.19%
2022, share of farmed seaweed production; world production in 2019 was over 35 million tonnes.
Where it goes next
Seaweed feeds 1 line directly.
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Sources
Cite this page: "How seaweed is farmed and harvested." Assembly Line, 2026-11-03. https://assemblyline.org/make/seaweed