Zanzibar Seaweed Farming: Who Grows It, Where to See It, and What It Becomes

Walk the east coast of Zanzibar at low tide between Jambiani and Paje and you will see rows of string stretched just above the sandy shallows, tended mostly by women. If you look more carefully, you will see the strings are covered in dark red-green growth — seaweed, bunched at intervals along each line, swelling over six to eight weeks into harvestable masses. This is Zanzibar’s seaweed farming industry: more than 23,000 farmers, 88% of them women, producing a commodity that ends up, processed and refined, in your ice cream.

What you’re seeing on the reef flat

Commercial seaweed farming started in Zanzibar in 1989 on the east coast, introduced as an alternative livelihood at a time when fishing — the island’s existing marine industry — was male-dominated and provided few income pathways for women. (Seaweed trading on the mainland dates to the 1930s, but modern aquaculture cultivation on Zanzibar began in 1989.)

The two species farmed are:

• Eucheuma cottonii (now classified as Kappaphycus alvarezii), known locally as kotoni or mwani. This is the dominant species. It produces kappa-carrageenan, a gelling agent used in dairy products, processed foods, and cosmetics.
• Eucheuma spinosum (now Eucheumatopsis isiformis), known locally as mwani mwekundu (red seaweed). This species produces iota-carrageenan, which has different gelling properties and is used in infant formula and some dairy applications.

The seaweed you see on the reef flat is not decorative, not accidental, and not wild. It is actively cultivated in one of the most significant women-led industries in East Africa — second only to fishing and tourism as an economic activity on Zanzibar, by some accounts.

Zanzibar’s annual seaweed production exceeded 16,500 metric tons in 2016. The industry is active in 83 villages across the island — 50 on Unguja (the main island) and 33 on Pemba.

How seaweed farming works

Seaweed is not grown from seed. It propagates vegetatively — farmers tie small cuttings of the seaweed to string lines at regular intervals. Those cuttings grow over approximately six to eight weeks into harvestable bundles, at which point the farmer cuts and removes them, dries them, and sells to a middleman.

The farms occupy a narrow coastal strip: typically 400 to 600 metres from shore, in water that is less than 2 metres deep at high tide. This is the intertidal zone — covered at high water, exposed or barely covered at low water. The farms extend from mid-intertidal into the shallow subtidal band, which is why their visibility is completely tide-dependent.

Working hours follow the tide table, not the clock. Farms are accessible on foot when the lagoon is shallow — during the 2 to 3 hour low-tide window. At high tide, they are fully submerged and unreachable. This means a farmer’s productive window shifts roughly 50 minutes later each day as the tidal cycle turns. On days when low tide falls at 06:00, women walk out at dawn. On days when it falls at 13:00, they work at midday in full sun. There is no choosing when to work: the sea decides.

Seasonal patterns: The dry season from June to October provides the most comfortable working conditions — lower temperatures, less heat stress on the crop. The Kaskazi wind season (December to March) brings higher temperatures, elevated sea surface temperatures, and increased risk of ice-ice disease.

Where to find the farms

The main seaweed farming area on Zanzibar is the east coast, where the tidal range is largest and the shallow intertidal zone most extensive.

Jambiani is the longest-established seaweed farming community and the best place for visitors who want to engage seriously with the industry. Dozens of farms are dotted along the coastline south of the main village. The Mwani Mamas co-operative here is internationally recognised — visited by USAID programmes, featured by UN Women, and covered by Vogue, which described them as nine women who harvest seaweed and process it into beauty products. A guided seaweed tour at the Mwani Zanzibar Centre in Jambiani costs USD 15 per person and lasts approximately one hour, including a seaweed juice or snack. The experience is more genuine than most “cultural tours” on the island: you visit real workers on a real production cooperative, not a managed display.

Paje has active seaweed farms visible along the reef flat at low tide, particularly in the southern section of the beach. The Seaweed Center in Paje supports more than 40 female seaweed farmers with an income-improvement programme that includes local product development and sales. A seaweed farming tour is marketed here as a tourism activity.

Michamvi (the peninsula where Matlai is located) has seaweed farms along the tidal flats. At low tide, the shallow reef flat empties and the string lines become visible — the farms here are part of the same east coast network, less visited by tourists than Jambiani but equally active.

Chwaka Bay is one of the most extensive seaweed farming areas on the island. The tidal range here is dramatic — at low tide, the seabed is exposed up to 1.5 to 2 kilometres from the shoreline, creating a wide working platform. The scale of the farms visible from the shore at low tide is significant.

Best time to observe: Any day when low tide falls in the early morning (06:00–09:00) is ideal — the light is good, the temperature is lower, and the greatest number of farmers are typically working. Check a tide table for your specific dates: search for “Jambiani” or “Zanzibar East” at tides.today.

What the seaweed becomes

After harvest, the seaweed is dried on the beach or on wooden drying racks — it typically takes 2 to 3 days in the sun to reach the dry weight required for sale. Dried seaweed is sold to middlemen who aggregate and arrange export. Eight companies were exporting seaweed from Tanzania as of 2010.

The primary commodity extracted from Zanzibar seaweed is carrageenan — a naturally-occurring polysaccharide (a gel-forming carbohydrate) extracted from the red algae. Carrageenan is used globally as a thickening, gelling, and stabilising agent. It appears in:

• Ice cream — prevents crystallisation and improves texture
• Infant formula — an approved thickener for specific formulations
• Dairy products — stabilises chocolate milk, cream, and processed cheese
• Processed meat — texture improvement and moisture retention
• Cosmetics and personal care products — gel consistency in lotions, creams, and shampoos
• Pet food — gelling agent in wet food
• Biodegradable packaging — an emerging industrial application

Zanzibar’s exports go to the United States, Europe, and Asia. Export volumes grew 123% year-over-year to reach USD 2.4 million in one 12-month reporting period — a figure that reflects the global demand for natural carrageenan alternatives to synthetic thickeners.

The gap between what a Zanzibar farmer receives for a kilogram of dried seaweed and what a food or cosmetics manufacturer pays for the same kilogram of processed carrageenan is very large. The value-chain mathematics are not in the farmer’s favour — which is why several development programmes have focused on local value-addition: processing the seaweed on Zanzibar rather than exporting it raw.

Local products are a partial response to this gap. Women’s enterprises in Jambiani and Paje have developed seaweed soap, seaweed body lotion, seaweed face scrub, seaweed tea, and seaweed-based snacks — finished goods sold in village shops, at guesthouses, and at Darajani Market in Stone Town. These products capture more value per kilogram than raw export.

The women’s industry — economics and independence

Seaweed farming is one of the most significant economic facts about Zanzibar’s east coast. Of the more than 23,000 farmers, 88% are women. The industry was partly designed with this in mind — introduced in 1989 to provide income pathways for women in a context where offshore fishing (male-dominated) and wage employment were largely unavailable to them.

The income is real. The Mwani Mamas in Jambiani are described as the first generation of women in Jambiani to achieve financial independence, earning approximately USD 250 to 300 per month — meaningful in a local economy with few alternatives. A 2012 study of Zanzibar seaweed farming found individual farmers earning between TZS 150,000 and 250,000 per month (approximately USD 96 to 160). Earnings vary significantly with season and disease pressure: harvesting cycles of 2 to 4 weeks can generate TZS 100,000 to 300,000 (USD 64 to 192) per cycle in productive seasons; average months can return TZS 50,000 to 60,000 (USD 32 to 38).

The social impact is documented. One WIEGO study found that seaweed income enabled some women to increase their clothing ownership from fewer than 5 pairs of khanga to up to 30 pairs — a concrete measure of purchasing power. The income has been described in peer-reviewed literature as contributing to a profound shift in gender relations on the east coast, with women gaining household decision-making influence they had not previously had.

The co-operative structure is significant here. When women pool buying conditions and negotiate collectively — rather than individual farmers selling separately to middlemen — they prevent the underselling that characterised the early years of the industry. The Mwani Zanzibar Centre in Jambiani, the Seaweed Center in Paje, and similar organisations in other east coast villages formalise this co-operative dynamic.

UN Tanzania has described seaweed farming in Zanzibar as “women at the heart of a blue revolution” — framing it explicitly as an ocean-economy story about female economic participation.

The challenges: ice-ice disease and low prices

The industry has faced two structural problems since its establishment.

Ice-ice disease

Ice-ice is a bleaching and deterioration condition that affects Eucheuma cottonii (and, to a lesser extent, Eucheuma spinosum). Infected thalli — the seaweed fronds — turn white, brittle, and then disintegrate on the cultivation line, destroying the harvest before it can be collected.

The triggers are environmental: high water temperatures (above approximately 30°C) and elevated salinity, both more likely during the hot season (roughly November to March). The warm months that coincide with the Kaskazi wind season are the highest-risk period. A severe ice-ice outbreak can destroy an entire farm’s production for that cycle — representing a complete loss of six to eight weeks of growth.

Research into the problem has focused on more resistant strains and on cultivation at greater depth, below the most thermally stressed surface zone. Climate change — which is raising baseline Indian Ocean sea surface temperatures — is expected to increase both the frequency and severity of ice-ice outbreaks. Some farmers have already exited the industry following repeated losses.

Low farm-gate prices

The price paid to Zanzibar farmers for dried seaweed has been consistently criticised as too low relative to the global value of processed carrageenan. The carrageenan market is dominated by processors in the Philippines, China, and Europe — entities that buy raw material from Zanzibar (and other producers) at commodity prices and then sell refined carrageenan at industrial prices to food and cosmetics manufacturers.

Development programs — including USAID-supported initiatives and programmes linked to UN Women — have sought to address this by encouraging value-addition on the island: local extraction and processing of carrageenan before export, or development of finished consumer products (soap, lotion, food ingredients) that earn higher margins. Progress has been slow. Raw seaweed export remains the dominant model.

Responsible tourism

The seaweed farms are part of the working fabric of east coast village life, not an attraction constructed for visitors. Some farmers will welcome observers who are respectful; the Mwani Mamas in Jambiani and the Seaweed Center in Paje have developed formal tour formats precisely to make these encounters structured and fair.

What visitors should and shouldn’t do:

• Don’t walk through working farms. The cultivation string lines and the growing seaweed attached to them can be disrupted by clumsy footfall. The reef flat at low tide looks flat and empty from a distance — the farms are not always obvious until you are among them.
• Ask before photographing. Women working in the water at low tide, often in the early morning, are not always expecting to be in tourist photographs. Asking permission takes 10 seconds and is the difference between a respectful encounter and an intrusive one.
• Book a guided tour if you want to engage seriously. The USD 15 guided seaweed tour at the Mwani Zanzibar Centre in Jambiani is money spent directly in the co-operative. It includes an explanation of the cultivation process, the chance to walk the reef flat, and usually a seaweed product tasting. This is a better model than wandering through working farms unannounced.
• Buy locally processed seaweed products. Seaweed soap, lotion, tea, and snacks available in east coast village shops and guesthouses are genuine local enterprises that capture more value than raw export. Quality varies; look for products from established co-operatives with consistent labelling.
• Wear reef shoes. The reef flat at low tide is sharp in places. Reef shoes are not optional.

Where to find seaweed products beyond the farm gate: East coast guesthouses in Jambiani stock them; some village shops along the Jambiani road sell soap and lotion. The Seaweed Center in Paje has products on site. Darajani Market in Stone Town sometimes carries seaweed products from east coast producers — check the craft and produce section near the main hall entrance.

Fifty women at low tide

From the Matlai terrace on Michamvi, the tidal pattern is visible every day. At high water, the reef flat is fully covered — a smooth blue-green expanse. As the tide drops, the flat begins to appear: first as pale patches, then as an unbroken walkable surface stretching a few hundred metres from the shore.

What happens next is immediate. Within minutes of the waterline receding far enough to expose the farm area, women walk out from the village. They carry baskets and move quickly across the wet sand to the string lines. They work in groups, some harvesting — cutting the grown bundles from the lines and dropping them into baskets — others tying new cuttings, starting the next six-week cycle. The pace is purposeful, not leisurely: they have roughly two hours before the tide turns.

On a productive morning low tide in the dry season, I’ve counted approximately 50 women working the stretch of reef flat visible from the property. They will have sold what they harvest today to a middleman, who will aggregate it with what other farms on this coast produced, and send it to a processor who will extract carrageenan from it. That carrageenan will end up, months later, in food and cosmetics supply chains in Europe, Asia, and North America.

The gap between what you are eating and where it was grown, by whom, under what conditions, is one of the more useful things Zanzibar tourism can teach — if you are paying attention at low tide.

For the full guide to Jambiani — the main village for seaweed farm visits, tour logistics, and Mwani Mamas co-operative contact — see the Jambiani guide. For the broader context of how to visit the east coast respectfully, including photography guidelines, community spending, and how to spot genuine eco-tourism from greenwashing, see the responsible travel guide. For accommodation on the east coast close to the seaweed farming areas, see the east coast where-to-stay guide. For the best time of year to visit — including which months have the most comfortable low-tide working conditions — see the when to go guide.