Low tide in Zanzibar is theatrical in nature. The change is so gradual that if you keep staring you won’t even notice it. But if you look away, even for a few minutes, it takes you by surprise. As the water withdraws, the blindingly white sand reveals itself to the scorching mid-afternoon sun. Small puddles of water create beautiful marks across the seabed and curious patterns of sticks begin to be seen. This is the time for tourists to take shelter under the beamed roofs of the hundreds of beach bars dotted along the coast. But for the local women of coastal Zanzibar, this is the time to work. They are growing seaweed and low tide is the only time when access to the farms is possible.

The work is tough: heavy bundles of sticks and seaweed have to be lifted, causing back pain, and the women’s skin is toughened by the elements. Their bare feet are peppered with scars from machete-like shells and sea urchins.

Seaweed grows like coral, so the women tie many small bits of seaweed to a piece of string, attach the string to two sticks and dig the sticks into the soft sand. After a week it will have grown substantially and can be harvested.

Seaweed farming is relatively new to the region. Initially, wild seaweed was simply collected by the locals, but when they discovered that specific species couldn’t be cultivated, several new species were imported from the Philippines and the first farm was put in place in the mid-1980s. It quickly became a successful commodity and is now the second-biggest earner, after tourism. In the beginning, however, exploitation was rife: farmers would carry out the backbreaking work and sell their harvest to foreign companies. But in its raw state seaweed is worth just 20 or 30 cents per kilo.

Farmers began to form unions to protect their rights and improve their situation. The Seaweed Cluster Initiative (ZaSCI) works with farmers, researchers and seaweed buyers to improve the quality of the seaweed and advocate the concept of adding value to the seaweed (by processing it into a powder or a gel, for example), thus allowing farmers to charge more for their product. At the Seaweed Centre, 32 women create soaps, oils and creams from the seaweed – and receive a stable wage for their work.

Many of them have managed to build their own house and send their children to school because of this income.

‘I am so grateful, because the centre keeps me busy and I get a stable salary at the end of the month. And now I have knowledge which I didn’t have before. Now I can make soap,’ says Shiba.

As well as learning how to make soap, the women have gained knowledge of and experience in business, conservation, farming techniques, and even foreign languages (the centre arranges for English-speaking students to come to learn Swahili from the women; in exchange, they teach them English).

But the members here are not without their concerns. They are aware of the physical strain they are under and of the marketing restrictions of their product. Most of all, though, they are concerned about the significant dip in seaweed growth. Something in the farming conditions has changed. ‘A year ago everything was fine. But it seems something is wrong with the sea... the seaweed doesn’t grow like before,’ says Mtumwa Imani Ali.

Klaartje Schade, who is CEO of the Seaweed Centre, believes there are several potential causes. ‘One is the breeding [of the plants]: seedlings need to be kept fresh. Another is the weather. Apparently it’s too hot. Of course, it might be the sea itself... properties within the sea...’ She remains positive, however, that a solution will be found; researchers are currently experimenting with a technique called deep-sea farming that aims to grow seaweed in deeper, cooler water.

Having come together in the past to challenge economic exploitation, the farmers now need to work together to solve an environmental challenge.

Watch Kat Zoulas’ documentary film Beneath the Tide on Indiegogo.