At about 10am every morning, women in hijabs and loose long dresses wade through Zanzibar’s turquoise shallow tides to tend their sponge farms – a new lifeline after climate change upended their former work.
Rising ocean temperatures, overfishing and pollution have steadily degraded marine ecosystems around this group of islands off the coast of East Africa. These environmental issues have undermined a key source of income for locals in Zanzibar’s Jambiani village who long depended on farming seaweed.
Now, they have turned to sponge cultivation under a project set up by Swiss NGO Marine Cultures.
Hot temperatures have killed the seaweed, and declining fish stocks have driven many fishermen to quit, said project manager Ali Mahmudi.
But sponges – which provide shelter and food for sea creatures – tend to thrive in warmer waters.
They are also lucrative as an organic personal care product and can be used for skin exfoliation. Depending on their size, they can fetch up to US$30 (HK$233) each, and a single farm can have as many as 1,500 sponges.
From the shore, black sticks can be seen jutting out of the water, holding lines of sponges.
Nasiri Hassan Haji, 53, recalled when she first learned about the practice more than a decade ago: “I was shocked to learn that sponges exist in the ocean.”
Haji, who is a mother of four, used to farm seaweed and described it as labour intensive with meagre returns.
In 2009, Marine Cultures launched a pilot farm with widowed women in Jambiani to test the potential of sponges in the archipelago, where more than a quarter of the 1.9 million population live below the poverty line.
With demand for eco-friendly products on the rise, the market for natural sponges has grown steadily, with the US National Oceanic and Atmospheric Administration estimating its value at US$20 million (HK$155.6 million) in 2020.
Many other women have now joined a cooperative to expand the sponge farm project in Jambiani, but it was not always smooth sailing.
“At first, I was afraid of getting into it because I did not know how to swim. Many discouraged me, saying the water is too much and I will die,” Haji said.
Thanks to an NGO programme, she learned to swim at the age of 39.
As well as making money for locals, sponges are beneficial to the marine environment.
Studies show that a sponge’s skeletal structure aids carbon recycling within coral reef ecosystems. Sponges are also excellent filter feeders, effectively removing suspended particles, bacteria and organic matter from the water.
This filtration process helps in maintaining water clarity and quality by reducing excess nutrients and contaminants (see graphic).
An estimated 60 per cent of the world’s marine ecosystems have been degraded or are being used unsustainably, according to the United Nations, which warned that the “ocean is in deep crisis”.
Sponges are also known to help restore coral reefs, which support 25 per cent of marine life and are currently under threat.
“What attracted me to this is the fact that we are not destroying the environment,” Haji said.
What is a sponge, and how is it different from a coral?
Sponges are simple aquatic animals. They have no real organs, and their skeletons can be made of minerals or a fibre-like protein, which is similar to a bath sponge.
Like corals, sponges live in water and are immobile invertebrates, which means they do not move.
Besides that, sponges and corals are completely different organisms.
Corals are complex animals with layers of tissue that help them function. Sponges are much simpler and do not have tissue.
All corals must live in salt water. While most sponges live in the ocean, many kinds of sponges can also be found in fresh water, such as rivers and lakes, and estuaries, which is an area where a river or stream meets the ocean.
