Coral cultivation offers hope to devastated western Indian Ocean reefs

by Wanjohi Kabukuru | Thomson Reuters Foundation
Saturday, 29 March 2014 08:15 GMT

Scuba divers swim past fish along a coral reef off the west coast of Zanzibar island, Tanzania, on December 4, 2007. REUTERS/Finbarr O'Reilly

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Marine scientists in the Seychelles are propagating corals resistant to bleaching in the hope of replacing destroyed reefs with ones that are more resilient

AMITIE, Seychelles (Thomson Reuters Foundation) – Marine scientists in the Seychelles are propagating and replanting corals resistant to bleaching in the hope of replacing destroyed reefs in the western Indian Ocean with ones that are more resilient.

Each workday, Claude Reveret and Sarah Frias-Torres of Nature Seychelles, a not-for-profit environmental organisation, lead a team of scuba divers down to the ocean floor around Praslin, the country’s second-largest island, and the nearby Cousin Island Special Reserve.

There they take part in an unusual undersea gardening project – cultivating corals that have proven resistant to the stress caused by warming water, which has led to the collapse of coral reef systems in the western Indian Ocean.

The large-scale death of coral reefs has exposed the Seychelles to increased erosion and the loss of fisheries that the reefs had harboured. The Indian Ocean island nations of Mauritius and Comoros and the eastern African countries of Mozambique, Tanzania, Kenya and Somalia are also affected. 

The restoration project, which began in 2010 with over $700,000 in funding from the US Agency for International Development and the UN Development Programme, “is our response to climate change effects,” says Reveret.

The western Indian Ocean suffered damage to its vast coral ecosystems in 1998 due to El Nino, a periodic atmospheric phenomenon that warms ocean currents. Intense El Ninos in recent decades have been linked by some scientists to climate change.

“Fishermen told us that ‘mawe ya bahari’ (stones of the sea), as they refer to corals, had changed colour,” says Obura, who at that time was studying marine life at the Kiunga Marine National Reserve near the Kenyan-Somali border. “In other words, they were all bleached.”

Frias-Torres  explained that coral bleaching occurs when higher than normal water temperatures and bright sunlight cause corals to expel the algae living in their tissues. The bleached coral eventually dies, and it cannot support other life, drastically affecting fisheries.

The effects of the 1998 El Nino were not limited to the Kiunga area. Ninety percent of corals in the western Indian Ocean, from the Mozambique Channel to the Seychelles archipelago and north to the Gulf of Aden, collapsed because of bleaching.

“This coral bleaching was a (wake-up) call,” said Kenyan marine scientist David Obura, who directs the East Africa programme of Coastal Oceans Research and Development in the Indian Ocean (CORDIO), based in the Kenyan coastal city of Mombasa.  

“It was probably the first time in recent history that the western Indian Ocean had experienced large-scale climate change effects,” he added.

Research by CORDIO and the Western Indian Ocean Marine Science Association (WIOMSA), a regional scientific body, has investigated the consequences of coral bleaching to island and coastal communities along the Indian Ocean rim. Coral reefs are not only essential to fisheries but also protect shorelines, reduce beach erosion and help control sea-level rise.   

The current restoration efforts in the Seychelles are trying to mitigate the damage by propagating corals from the few coral colonies that managed to withstand the effects of El Nino.


Following an ecosystem survey which identified eight resilient species of coral, fragments of them – called “nubbins” – were chiselled from donor colonies within the Seychelles archipelago and used to establish nurseries around Cousin Island.

“We harvested (the nubbins) and tied them to nylon ropes of 20 metres (65 feet) each,” Reveret said. “We have two types of nurseries, the rope and net nurseries, which make up our coral propagation garden.”

Eight rope nurseries with 40,000 nubbins have so far been established. The nurseries are monitored and the coral cleaned with hard brushes each day to accelerate growth.

“By attaching the ropes into the sea floor ... the corals can sense the sea bed and attach themselves and grow,” Fries-Torres said.

Reveret said corals take from six months to a year to grow to the point where they can be transplanted, depending on the species.

Help also comes from the humphead parrot fish. The fish eat algae that would otherwise stunt coral growth, and their excrement is believed to provide the coral with nutrition.

Nirmal Shah, who heads Nature Seychelles and serves as president of WIOMSA, said the scientists studied similar restoration endeavours in Haifa in Israel and in the Dominican Republic before beginning the reef restoration project four years ago.

“For the last four years we have propagated resistant corals from scratch and in the last few months we have been involved in transplanting them from the garden nurseries to the actual restoration sites,” Shah said.

According to Shah, 11,000 coral colonies, covering an area of about 4,800 square metres, have been transplanted.

“The nursery has been a success so far and we grew more corals than we expected,” he adds.

Although the project is currently limited to the Seychelles, Shah says that Nature Seychelles will share its knowledge and offer training to their western Indian Ocean neighbours.


According to the US National Oceanic and Atmospheric Administration (NOAA), the global benefit accruing from corals stands at $29.5 billion annually. Globally around 500 million people rely on corals for food, livelihoods and coastal defence.

“Coral reefs are one of the most sensitive ecosystems to climate change and the corals in this region have been quite disturbed,” said Tim McClanahan, a senior conservation zoologist with the Wildlife Conservation Society in Mombasa.

“If reefs and fisheries were better managed they could contribute more to food security,” McClanahan added. “Weak management is undermining their potential.”

Shah concurs with McClanahan and notes that fish catches in the western India Ocean have declined by 20 percent in the last two years.

“We are tied (together) by the Indian Ocean ecosystem, and even though the conservation approaches to climate change responses are different ... they are all aimed at the common good of the sea,” CORDIO’s Obura said.

(Rewriting and editing by James Baer)

Wanjohi Kabukuru is a freelance journalist specialising in environmental affairs and based in Nairobi, Kenya.

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