Seaweed farming
Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form farmers gather from natural beds, while at the other extreme farmers fully control the crop's life cycle.
For the process of collecting seaweed as a hobby, see Seaweed collecting.
The seven most cultivated taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Eucheuma and K. alvarezii are attractive for carrageenan (a gelling agent); Gracilaria is farmed for agar; the rest are eaten after limited processing.[1] Seaweeds are different from mangroves and seagrasses, as they are photosynthetic algal organisms[2] and are non-flowering.[1]
The largest seaweed-producing countries as of 2022 are China (58.62%) and Indonesia (28.6%); followed by South Korea (5.09%) and the Philippines (4.19%). Other notable producers include North Korea (1.6%), Japan (1.15%), Malaysia (0.53%), Zanzibar (Tanzania, 0.5%), and Chile (0.3%).[3][4] Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.[5]
The Food and Agriculture Organization (FAO) reported that world production in 2019 was over 35 million tonnes. North America produced some 23,000 tonnes of wet seaweed. Alaska, Maine, France, and Norway each more than doubled their seaweed production since 2018. As of 2019, seaweed represented 30% of marine aquaculture.[6]
Seaweed farming is a carbon negative crop, with a high potential for climate change mitigation.[7][8] The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.[9] World Wildlife Fund, Oceans 2050, and The Nature Conservancy publicly support expanded seaweed cultivation.[6]
Zanzibar's seaweed growers face a changing climate. Here, a farmer tends to her farm in Paje, on the southeast coast of the island.
Mwanaisha Makame and Mashavu Rum, who have been farming seaweed on Zanzibar island for 20 years, wade through the low tide to their farm.
The seaweed grows underwater for 45 days. When it reaches one kilogram it is picked and dried, then packed in bags to be exported to countries like China, Korea, and Vietnam. There, it is used in medicines and shampoos.
The farmers have a lot of problems due to climate change. Two decades ago, 450 seaweed farmers roamed Paje. Now, only about 150 farmers remain.
Mwanaisha holds up a healthy clump of seaweed. Then she holds up seaweed the farmers will not be able to use. A hard white substance grows on it—ice-ice disease, caused by higher ocean temperatures and intense sunlight.
The seaweed farmers learned how to make soap from their seaweed at the Zanzibar Seaweed Center, a business that started as an NGO in 2009. At their homes, they mix water, ground seaweed powder, coconut oil, caustic soda, and essential oils in a large plastic tub.
Later in the week, the seaweed farmers will sell their finished soaps in Zanzibar town or to regular local customers. As seaweed levels decline, they have found a way to increase the value of their work.
The finished product—a bar of seaweed soap
