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Our Burning Planet

South African team helps to restore Zanzibar’s degraded coral reefs 

South African team helps to restore Zanzibar’s degraded coral reefs 
Coral restoration team leader Dr Camilla Floros (left) and Mnemba Island coral ambassadors Washington Denis, Hija Uledi, Nassor Ali and Haji Ali on 25 January 2024. (Photo: Supplied)
Tony Carnie
By Tony Carnie
10 Sep 2024
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Surveys suggest that coral cover around the tiny island of Mnemba has declined by nearly 90% over the last two decades owing to climate change and ‘overtourism’. A group of South African scientists are trying to reverse the trend.

Spectacular coral reefs, clear blue seas and white sand beaches are some of Zanzibar’s major drawcards, helping to attract more than 100,000 tourists every year.

But the financial benefit of this increasing tide of “overtourism” is putting further strain on the colourful reef attractions that are already getting battered by the impact of climate change.

South African marine scientist Dr Camilla Floros notes that there was an “unprecedented warming event” along sections of the East African coastline earlier this year, when sea water temperatures rose to 31°C to a depth of 30m.

These unusually high temperatures, which lasted for nearly a month, are bad news for many corals that can only thrive within a narrow temperature band. 

Floros says that if such unusually high temperatures persist for more than two weeks, the corals start to “bleach”. 

(Healthy corals derive their colour from the algal species that live in their tissue – but when water temperatures get too high the stressed coral polyps start to expel the algae, exposing their white skeletons). 

Simultaneously, the corals also lose their ability to obtain food from the algae, eventually killing the coral if high temperatures don’t drop.

Now add a stream of tourists arriving daily in a small armada of tour boats to snorkel among the coral reefs.

Coral reefs in Zanzibar Up to 200 tour boats a day are placing unsustainable pressure on Mnemba’s coral reefs in Zanzibar. (Photo: Supplied)



In addition to boat hulls, anchors or propellers scraping against the reef, some tourists also harm sensitive corals by touching and standing on them.

These are some of the reasons an ambitious coral conservation project has been launched off the coast of Zanzibar, with funding from the G20 Coral Research & Development Accelerator Platform (Cordap).

The project is centred on the tiny island of Mnemba near the northern tip of Unguja, the largest island of the Zanzibar archipelago (which includes Pemba and Mafia islands).

Floros, principal scientist of the Wild Impact group, is leading the restoration project, along with Dr Sean Porter of the Durban-based Oceanographic Research Institute (ORI), Stuart Laing, a former ORI researcher now based at the University of Seychelles, and Dr Narriman Jiddawi of the University of Dar es Salaam.

The team has just been awarded $800,000 by Cordap to upscale an existing coral restoration project at Mnemba.

Floros says the target is to increase coral cover on degraded reefs by 10% within three years, reduce the tourist pressure and enhance biodiversity and habitat quality. 

Mnemba, with a circumference of just 2km, is surrounded by coral reefs that have become one of Unguja’s “hotspots” for snorkelling. Up to 200 unregulated tourist boats visit a small section of the reef daily and recent surveys suggest that coral cover has declined by nearly 90% over the last two decades.

With just 10% remaining, Floros says it is critical to arrest further damage and to start restoring and regenerating coral cover around Mnemba. 

Working with Tanzania’s Ministry of the Blue Economy and Fisheries, Floros and her colleagues are hoping to regulate and reduce the number of snorkel boats.

They don’t aim to stop tours entirely, but rather reduce the number significantly and encourage tour operators to recoup volume losses by charging a higher fee to fewer visitors.

The researchers also aim to significantly expand the size of artificial coral reefs and the coral nursery set up three years ago.

To expand the artificial reef, dislodged coral fragments are collected and then nurtured in a coral nursery before being planted out to new artificial reefs or along degraded sections of the main reef. 

Coral reefs Fragments of Acropora corals growing on an underwater nursery table at Mnemba on 22 August 2024. (Photo: Supplied)



“As soon as you put down additional habitat, the marine life starts to congregate and the coral also sets by itself. Juvenile fish use it as a nursery, along with starfish, sea urchins and other species,” Floros says.

“Currently we have six artificial reef structures and the aim is to increase this number to at least 18.”

“Increasing coral cover on Mnemba’s degraded reef by 10% over the next three years is an ambitious target – but that does not mean we must not try,” she says.

“There are some locally indigenous coral species that have a natural ability to withstand higher temperatures or to recover more quickly after bleaching events, so we also want to harvest more of these species and incorporate them into sections of the damaged reef.

“Coral reefs are critical to healthy oceans. They cover less than 1% of the world’s oceans but provide habitat for 25% of marine species.”

Local ambassadors


coral reefs Coral restoration team leader Dr Camilla Floros (left) and Mnemba Island coral ambassadors Washington Denis, Hija Uledi, Nassor Ali and Haji Ali on 25 January 2024. (Photo: Supplied)



Much of the hands-on work will be done by a team of local community and conservation rangers trained to act as ambassadors for the project, while also collecting and replanting corals. 

A further dimension of the project is to expand ocean literacy programmes at 14 local schools. This will include employing graduate students to teach a dedicated marine curriculum, while marine economist Stuart Laing will conduct a separate study to better understand community perceptions of marine restoration.

The Zanzibar project is one of eight coral research and restoration projects across the world that have been awarded a total of $8.5-million in funding support by Cordap.

https://www.youtube.com/watch?v=PCqhhkHafSk&ab_channel=andBeyond

While several are focused on restoration, one of the projects aims to establish the first cryo-repository network for coral larvae in the Coral Triangle around Thailand, Malaysia, Indonesia and the Philippines

Cryo-preservation is a process where biological material is cooled to very low temperatures, allowing it to remain alive but inactive until it is needed again.

A second, more controversial project – conducted by the University of North Carolina Wilmington and the University of the Philippines – involves genetically engineering corals to withstand higher sea temperatures. This team is using a series of micro-injections and genetic modifications featuring CRISPR, a gene-editing technology that allows scientists to directly modify DNA. DM

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