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Local threats to mangroves in the Western Indian Ocean region identified in new study

GEF-UNEP/Nairobi Convention WIO-SAP

By IW:LEARN

December 8^th, 2021

A version of this article originally appeared on www.nairobiconvention.org.

In one of the most encouraging pledges to come out of the recent 26th Conference of Parties to the UN Framework Convention on Climate Change (COP26), leaders from more than 100 countries pledged to end deforestation by 2030. The landmark agreement covers around 85% of the world’s forests.

Yet, when we think about the trees that make up these forests, many may imagine the tropical forests of the Congo basin, the snow-capped pines of Siberia, the towering redwoods of California, or the leafy palm trees of the Amazon. Mangroves, on the other hand – unique trees that thrive in saltwater and dot tropical coastlines around the world – may not immediately come to mind when we think about the need to stop deforestation.

But they should.

Photo credit: Matt Curnok / Ocean Image Bank

Mangroves are among the most productive ecosystems on earth. Not only do they protect shorelines from eroding, shielding us from floods, hurricanes, and storms, but they also provide nursery areas for fish, crustaceans, mollusks, and more, while supporting many threatened and endangered species. Globally, mangroves provide goods and services estimated to be worth billions per year, including 65 billion USD in shoreline protection alone. What’s more, they can store up to five times more carbon than terrestrial forests, making them crucial weapons in the fight against climate change.

But for many communities, including those in the Western Indian Ocean region, they are worth much more. Coastal residents eat or sell the fish who live around the mangroves, while others use their wood as building material and fuel to use themselves or sell—underscoring the importance of mangroves to both economic and food security. Yet the region has lost 20-33% of its mangroves in the past 25 years alone, a trend that—if left unchecked—is only likely to accelerate with rapid increases in population and coastal development.

A new study published in the Wiley Journal of Global Ecology and Biogeography has determined that both human pressures, when coupled with erosion, drought, and sea-level changes (i.e. certain effects of climate change), are the main culprits behind the diminishing mangrove forests in the Western Indian Ocean region.

These and other causes of mangrove degradation – which include both human pressures (logging, land-use conversion, etc.) and the effects of climate change (i.e. sea-level rise, erosion, ocean climate, etc.) are well-known. However, not all mangroves suffer equally from these drivers of deforestation. In order to create tailored responses to address mangrove degradation in different regions, therefore, a greater understanding of how mangroves are affected at a local level by these factors is necessary.

This study, supported by the Nairobi Convention’s WIOSAP project and the Western Indian Ocean Marine Science Association (WIOMSA), examines the level of exposure to threats to mangroves in Kenya, Madagascar, Mozambique, and Tanzania. It finds that human pressure, erosion, drought, and sea-level changes are the main drivers of changes in mangrove cover in these four countries.

Specifically, mangroves in Mombasa and Kilifi, Kenya were severely threatened due to erosion, human pressure, and sea level. Mangroves in Lamu were only moderately exposed, however, while Kipini, southern Kenya, and Mida were low to moderately exposed.

In Tanzania, Pangani in the north, Bagamoyo in the centre, Lindi and Kilwa in the south, and Unguja were severely exposed because of high erosion, sea-level anomalies, and human pressures. Kilwa, for its part, was exposed as a result of land development intensity and drought conditions, while Tanga, Mafia, Mtwara and Rufiji were the least exposed mangrove areas in Tanzania.

In Mozambique, though exposure was low or moderate in several areas (namely, Inhambane, Zambezi, and Vilankulos), Angoche and Nacala were highly exposed due to sea-level anomaly, drought, and erosion. Maputo Bay and Nhangau (north of Beira town), meanwhile, were also severely exposed to human pressure, land development intensity, and erosion.

In Madagascar, however, all mangrove regions ranked as severely exposed, although the reasons for this exposure varied across the country. Northwest, southwest, and western Madagascar were all highly exposed to erosion, for example, while the southwest was also severely exposed to sea-level anomalies. While mangroves in Madagascar were all exposed to drought conditions, they were overall less impacted by human pressure than other countries in the region.

This variety demonstrates why it is so important to understand the main drivers behind the degradation of a certain mangrove area, so that tailored, adaptive management approaches can be applied. Depending on the driver of change, these adaptive management tools could include establishing buffer zones, awareness-raising, enforcement of anti-logging rules, and mangrove rehabilitation and restoration.

UNEP - Nairobi Convention and WIOMSA’s recent Guidelines on Mangrove Ecosystem Restoration for the Western Indian Ocean region could be helpful in this regard, as they analyze risk factors and challenges facing restoration projects and provide possible solutions. By understanding the specific drivers of change and then adapting responses accordingly, governments, donors and other managers of restoration projects can ensure that their investments are used wisely—thus reducing the amount of wasted effort and resources and increasing the benefits provided by this critical habitat.

Mangrove forest located in the Mida Creek - Malindi. Photo credit: Timothy K, Unsplash

About the WIO-SAP Project

WIO-SAP is working ‘to reduce impacts from land-based sources and activities and sustainably manage critical coastal-riverine ecosystems through the implementation of the WIO-SAP priorities with the support of partnerships at national and regional levels’. The project builds on the WIO-LaB Strategic Action Programme (SAP) for the protection of the WIO Region from land-based sources and activities that was developed under the auspices of the GEF-UNEP WIO-LaB project and which identified key actions that need to be undertaken in the region in order to reverse the degradation of the coastal and marine ecosystems.

For more information on this project, please contact the Project Manager, Jared Bosire (jared.bosire@un.org). Additionally, please access the project on the Nairobi Convention website and the dedicated project page on iwlearn.net.