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sustainable seaweed aquaculture
Spinosum seaweed farmed in Pemba.

Seaweed is farmed in coastal waters all over the world. Once dried, it's bought and processed by large corporations to produce carrageenan gum, a common food additive. Pemba has about 16,000 seaweed farmers living in more than 100 coastal villages, and is the most important seaweed farming area in Tanzania. About 8,000 tons of dried seaweed are produced each year in Pemba, which translates into an annual income for a farmer of $100-200.


Seaweed sales are the largest source of outside revenue in Pemba, larger than cloves, and provide an essential income for the farmers, who are all poor.  60% of the farms are run by women, and the whole family will be involved at various stages.


Seaweed farming is very hard work: people wade into the shallow water at low tide, and spend hours at a time tending networks of ropes, strung between wooden stakes, on which the weed hangs.


As important as this industry is, there is also a big concern: the wooden stakes, which are up to about 4 feet long, rot in the water. They have to be constantly replaced, and the most common source is the mangrove forests which grow near most seaweed-farming villages.


The farmers need an enormous number of stakes -- as many as 5 million a year Pemba-wide -- and this is a long-term threat to the mangrove forests, which are essential for healthy marine life in coastal waters. It's estimated Pemba is losing about 1-2% of its mangrove forests each year.


We have partnered with the University of Hawaii Department of Natural Resources and Environmental Management, and an international NGO, the World Agroforestry Centre (ICRAF) Tanzania office to develop concepts for sustainable production of seaweed farming stakes. Options we are looking at range from agroforestry plantations close to coastal villages and run by communities, to introduction of an ecosystem-based mangrove harvest, combined with a program of mangrove restoration. In 2017 we hosted a University of Hawaii graduate student, Genelle Watkins, for an intensive study of mangrove use in seaweed farming villages. Genelle's report will help guide our efforts to support seaweed farmers and conserve mangrove forests in Pemba.


The Pemba Foundation has previously conducted mangrove restoration programs, described here.