Saved by sponge

As oceans warm up, women in Zanzibar switch from seaweed to climate-resilient sponge farming to stay afloat

By Kizito Makoye
Published: Saturday 06 January 2024
Nasir Haji, chairperson of the Sponge Farmers Association, inspects her underwater sponge farm in Jambiani coast of Zanzibar (Photographs: Kizito Makoye)

Amid the refreshing breeze caressing Zanzibar’s Jambiani coast, Hindu Rajabu wades through knee-deep water to a lagoon. Wearing swimming goggles and a snorkel perched on her headscarf, the 31-year-old mother of two cautiously navigates the Indian Ocean to locate her floating sponge farm.

Rajabu is among a handful of women in Jambiani village who in 2020 started to cultivate natural sponges. These fascinating animals are made of loosely arranged cells that surround a skeleton of fibres. The specialised cells, nestled within thousands of tiny chambers, act as microscopic pumps, tirelessly drawing water into the sponge’s body with their whip-like tails. This unique pumping mechanism, which helps sponges extract nutrition and oxygen, also purifies the ocean water by removing impurities, including sewage. These sponges are also used for bathing and general hygiene because they are naturally antibacterial and antifungal and can resist odours.

With the tide gently rising, Rajabu submerges herself to reach the buoys cradling the sponge farm. Carefully, she inspects the sponges, suspended from thick polyethylene ropes. Using a knife, she removes any fouling organisms, such as bacteria and fish, which have attached themselves to the ropes. This periodic cleaning is essential to prevent the sponges from being overwhelmed by these unwanted inhabitants. The sponge farms are made of multiple ropes that run parallel to each other. They have sponges at different development stages. “We usually harvest them once a week when we collect the sponges that are big enough to be sold in the market,” says Rajabu. Women typically dive deep into the ocean to collect healthy wild sponges, which serve as the foundation for their farms that are set up close to the seashore where water is up to two metres deep. These sponge colonies are then carefully cultivated and fragmented to promote new growth.

Once the sponge is ready for harvesting—a natural process that takes six months to a year—Rajabu, along with 12 other women from the village who are also involved in sponge farming, label the sponges and sell them to hotels and tourists.

Adapting to warming

Rajabu has lived most of her life in poverty. She dropped out of school at the age of 17 to get married, and her financial troubles worsened when her husband left her and their two children. She initially joined the once-thriving seaweed farming sector that employs over 20,000 women in Zanzibar, a semi-independent archipelago within Tanzania. But her income gradually started to shrink due to the impact of climate change on seaweed, a group of macroscopic, multi-cellular marine algae that is used in medicines to treat a variety of ailments, including cancer, diabetes and gastric disorders. Climate change has made water temperatures in shallow lagoons too hot for seaweeds to survive.

Seaweed farming was introduced in Zanzibar in 1989, as per an article published in Springer in 2021. The industry grew rapidly, with Tanzania’s annual production increasing from 800 tonnes per year in 1990 to about 11,000 tonnes in 2002. Production plummeted by 47 per cent between 2002 and 2012, due to global competition and seaweed die-offs linked to climate change (increased temperatures, winds and irregular rainfall) and overgrowth of fouling organisms, says the article titled Adaptation of Seaweed Farmers in Zanzibar to the Impacts of Climate Change.

Desperate for financial independence, Rajabu enrolled with Marine Cultures, a Swiss-based non-profit that has been training women in sponge farming since 2009. The shift increased her income almost fourfold, and she now earns 250,000 Tanzanian shillings (US $100) per month. She recently purchased land where she is building a three-bedroom house.

Each harvested sponge is sold for 37,000-74,000 Tanzanian shillings ($15-30), says Nasir Haji, chairperson of the Zanzibar Sponge Farmers’ Cooperative, set up by the 12 sponge farmers in the village to forge tie-ups with shopkeepers and hotels. Farmers receive 70 per cent of the earnings, while 29 per cent goes to the shops, and the remaining 1 per cent supports the Zanzibar Sponge Farmers’ Cooperative.

(Left) Juvenile sponges bobbing on polyethylene ropes in an underwater farm in Zanzibar. 
(Right) Women from Jambiani village earn around  US $100 a month from selling these farmed natural sponges that are used 
for bathing

Soft yet resilient 

Sponges, unlike seaweed, possess remarkable resilience to climate change, require minimal maintenance, and command premium market prices, according to marine biologist Aziza Said from the University of Dodoma, Tanzania. Additionally, sponge farming requires little financial resources and technical expertise, as these organisms grow and propagate naturally.

Most sponges are hermaphrodites, harbouring both male and female reproductive organs, enabling them to self-propagate effortlessly. New sponges emerge from small buds that detach from the parent sponge and begin independent growth. Even damaged or fragmented sponges can regenerate into new individuals. This remarkable regenerative ability underpins the ease and feasibility of commercial sponge farming.

“Unlike synthetic sponges, sea sponges are free from harmful substances like chemicals and microplastics,” says Ali Mahmudi Ali, manager of Marine Cultures.

Christian Vaterlaus, founder of Marine Cultures, says they are struggling to scale up the operations. “We currently do not have the resources or expertise to build a hatchery to produce small baby sponges on the farm,” he adds.

Leonard Chauka, molecular biologist with the University of Dar es Salaam in Tanzania, highlights the time-intensive nature of sponge farming. “While sponge farming offers numerous benefits, only a few have ventured into it due to the time required for sponges to reach marketable size,” says Chauka.

Despite these challenges, the Zanzibar sponge market remains vibrant. Marine Cultures is expanding sponge farming to Pemba Island and Tanga City, empowering more women like Mkasi Abdalla, a widow and mother of seven who views sponge farming as a blessing.

Beyond Zanzibar, the global sea sponge market thrives in regions such as the Federated States of Micronesia and Tunisia. Valued for their natural beauty, exceptional softness, and sustainability, sea sponges offer an eco-friendly alternative to their synthetic counterparts, which are widely used in households worldwide.

This was first published in the 16-31 December, 2023 print edition of Down To Earth

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.