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Western Indian Ocean mangroves' secrets
Ilha da Inhaca, Mozambique

Western Indian Ocean mangroves' secrets

Mangroves are fascinating trees. 

At the breathtaking Rufiji Delta in Tanzania where the River Rufiji empties into the Indian Ocean, an interesting story is narrated by a resident Richard Mtila. 

“In 1987 the Tanzanian government imposed a moratorium on mangroves cutting in the Rufiji Delta to protect the expansive mangroves forests in Tanzania as the harvesting of poles had gone beyond control.” Mtila says. “This policy was impossible to enforce and it led to bad relations between coastal communities and the government. It actually ended up endangering mangroves as illegal cutting of mangroves continued.”

Four years later the government was forced back to the drawing board. However, this time around the government was smarter. It sought to know first why its policy had failed before coming up with another policy. 

“In 1991 a government led study revealed that the government failed to include community participation in mangrove conservation and in 1997 the Tanzanian government changed its forest law to allow for community participation.” Mtila says. “The hard lessons had been learned. And those lessons came from mangroves and coastal communities.”

Indeed Tanzania’s mangroves forests lessons led it to become among the first countries in Africa to accommodate communities in forest management and conservation. This template would later be borrowed by many African nations.

Though not as revered as many other trees, mangroves legendary history is acknowledged in the cross continental trade between the Middle East and Africa during the Monsoon trade. A passage in P.K Warne’s book – Let them Eat Shrimp makes some startling revelations.

“The mud roofs of Oman and Basra were supported by the mangroves rafters of Zanzibar and Rufiji. Dhows sailed from the Persian Gulf to Africa during the northeast monsoon bringing dates, carpets and earthenware and returned during the southeast monsoon with poles, firewood and mangrove bark for tanning. The mangrove pole trade was so important that each grade of pole had its own name – from spindly inch-thick fito used by the hundreds as reinforcing rods by the hundreds in the mud walls of Swahili houses to foot thick vigongo used as load bearing girders in multi story buildings.”

Mangroves logs ready for sale and export at Mokowe Jetty [Image: IOO Archives]


A third of global mangroves have been destroyed since World War 2 according to UN Food and Agriculture Organisation. 

Previously owing to ignorance, mangroves forests were largely viewed with disdain as abodes of pesky pests. According to Narriman Jiddawi of the Institute of Marine Studies at Tanzania’s Dar es sallam University, for generations mangroves forests were not even classified as forests but largely seen as “worthless mosquito infested areas.” This viewpoint has since changed and in the last two decades, extensive research both social and marine science has been conducted on these coastal ecosystems. 

The result has led to a complete reevaluation of mangroves.

Due to intensive studies, new knowledge has since emerged that not only traces their social importance and ecological roles but also quantifies their economic value at the same time. 

“The management of coastal ecosystems such as mangroves, saltmarshes and sea grasses has been identified as an important missing piece in international and national climate change mitigation strategies.” Dorothee Herr of the International Union for the Conservation of Nature (IUCN) says. “Mangroves, saltmarshes and seagrasses store significant amounts of carbon in the sediment, show ongoing sequestration and release this carbon if degraded or converted to the land-use activities.” 

Findings by David Obura of the Coastal Oceans Research and Development – Indian Ocean (CORDIO) who recently together with the World Wildlife Fund (WWF) and the Boston Group indicate that the western Indian Ocean’s total asset base is at least $333.8bn. In their report “reviving the Western Indian Ocean Economies” Obura and his team found out that the estimated worth of the region’s mangroves stand at $42.7bn. And according to the Nature Conservance one hectare of mangroves can offset emissions from 726 tonnes of coal.

The importance of mangroves and related coastal wetlands in carbon capture explained in this Nature Conservancy Infograph [Image: TNC]


10 species of mangroves are found in the western Indian Ocean region. According to David Obura of the Coastal Oceans Research and Development – Indian Ocean (CORDIO) the western Indian Ocean region covers some “30 million square kilometres and supports some 60 million people living within 100 kilometre of the shoreline.”   To this end mangroves act as shoreline defenses and protect shores against erosion not to mention myriad other uses and ecological functions.

The Eastern and Southern African coast which forms the core shelf of the western Indian Ocean has well developed mangroves forests with Somalia, Kenya, Tanzania, Mozambique, South Africa and the island states of Madagascar, Mauritius, Seychelles and Comoros hosting this rich and lush biodiversity estimated to cover a total of 1,000,000 ha in the entire WIO. 

Some 90 per cent of the mangroves forests in the region occur in the deltas of Zambezi in Mozambique, Rufiji in Tanzania, Tana in Kenya and Toliary in Mozambique. 

Mozambique boasts of the largest mangroves cover in the region with a coverage area of some 305,400ha of mangroves forests mainly occuring in Sofala and Zambezia provinces in Morumbane estuary, Inhambane Bay and in the Zambezi River Delta. The Mozambican coastline stretches a distance of 850km square. In 1972 Mozambican mangroves covered a total area of 408, 079ha. 

Madagascar harbours some 278,078ha of mangroves with the main forests area being found in Hahavavy, Nosy Be, Mahanjaga Bay, Melaky, Diana and Boeny. Tanzania has 133, 500 ha of mangroves occurring in the Pangani, Rufiji, Ruvuma areas whilst South Africa has 3600ha of mangroves. Somalia has an estimated 1000ha of mangroves. Kenya has 54,000ha and 18 mangroves formations along its 574km coastline. 

Mauritius and Comoros have the least mangrove coverage in the region accounting for some 145ha and 125ha respectively.  Much of the mangroves forests in these two island nations are nestled in the islands of Agalega and Rodrigues in Mauritius and in the Comoros they are found in Mapiachingo area in Moheli island. 

Inspite of its extensive coastline covering two oceans of Indian and the Atlantic Oceans, South Africa’s mangroves forest is a minuscule 3000ha mostly found in the border with Mozambique along the Nahoon and Mhlathuze estuaries. The mangroves forest cover in Seychelles covers some 2900ha mainly found in the main islands of Mahe, Praslin, La Digue and Silhouette. More extensive mangroves coverage is also seen in the Cosmoledo and Aldabra Atolls. Sporadic mangroves are spread out all over the 115 islands which make up this Indian Ocean archipelago. The picturesque creeks of Burgavo, Istambul and Kudha and the Juba –Shebelle estuaries host much of Somalia’s estimated 1000ha of mangroves.

According to region-wide studies conducted by the Zanzibar-based regional scientific marine think-tank the Western Indian Ocean Marine Science Association (WIOMSA) there are a number of threats facing mangroves. These include over harvesting for charcoal, timber, firewood, and even pollution. The other threats include rapid urbanisation due to increased population, clearing mangrove forests and converting the former mangroves forests to give room for solar salt harvesting, tourism purposes, aqua-culture mainly shrimp farming, agriculture and even urban development. 

Examples abound in the western Indian Ocean of the worrying loss of Mangroves forests. These include the clearance of 500ha of mangroves forests like it happened in Magarini in Kenya’s north coast to pave way for solar salt production. An accidental oil spill in the Port Reitz area in Mombasa, Kenya in 2005 completely damaged some 200ha of mangroves’. The 1998-1999 El Nino phenomenons not only led to the bleaching of corals but also damaged 500ha of mangroves habitats in the Mwache Creek along Kenya’s Tana Delta region. 

Presently the construction of the proposed $25.7bn Lamu Port South Sudan Ethiopia Transport (LAPSSET) Corridor has seen extensive clearance of mangroves forests in Lamu. The acreage of the mangroves clearance in Lamu is yet to be established and quantified as mangroves forests are expected to be cleared for the construction of a 32-berth port, oil-refinery plant, international airport, coal-fired power plant and a resort city. Lamu hosts 33,500ha which more than half of Kenya’s mangroves forest. Research by the Food and Agriculture Organisation shows that between 1985 and 2010 Kenya lost some 18 per cent of its mangroves. The mega construction projects currently planned for the coastal region in terms of roads and ports expansion signify that the trend of mangroves losses is set to continue. 

Plastic pollution is among the major threats to mangroves ecosystems in the western Indian Ocean [Image: IOO Archives] 



In Mozambique the construction of Cabora Bassa Dam resulted in the loss of 2000ha of mangroves forest; across the entire western Indian Ocean region. Xefina Pequena and Benguelene islands in Mozambique lost 25 per cent and 40 per cent respectively of their mangroves forest due to overharvesting.  

Construction of tourism facilities and other development centred activities has seen Mauritius losing close to 30 per cent of its mangrove cover. The same scenario has played out in Praslin Island in Seychelles, Iconi, Grande Comore and Anjouan in the Comoros.

In Tanzania, Somalia and Madagascar clearance for shrimp farming, sedimentation and coastal erosion have led to extensive degradation of some mangrove forests. Seychelles mangroves coverage has remained stable for the last decade and Mauritius has embarked on a mangroves restoration campaign. The Mauritius and the Gazi Bay mangroves restoration initiative in Kenya are worth mentioning under the backdrop of warning issued by the Global Oceans Commission (GOC) which notes of the dangers of climate change to the environment. “Climate change and ocean acidification are an increasing threat to the ecological health and biodiversity of the marine environment. On a timescale of decades and longer, they will overshadow all other threats.” GOC says in its study, Climate change, Ocean acidification and Geo-engineering. “The primary cause of both trends is emissions of carbon dioxide and other greenhouse gases from industry, transport and other human activities. International action to constrain emissions has been insufficient. Measures to improve the resilience of marine ecosystems have been proposed, but these can only be effective in the long run if serous reductions in carbon dioxide emissions are achieved.”

Article written under the aegis of the Centre for Science and Environment (CSE) Media Fellowships Programme