Mangrove forests provide a wide array of critical ecosystem services1, making them incredibly valuable and ecologically important.  Mangroves contribute to increased human wellbeing, successful climate mitigation and adaptation, and the conservation of biodiversity worldwide.

Increased Human Wellbeing

Mangroves contribute significantly to the human wellbeing of the coastal communities that they adjoin.

First, mangroves help to provide food security for local communities.  Mangroves serve as nurseries for many fish and other marine species2, without which many fisheries, including local coastal fisheries as well as commercial coastal and offshore fisheries, would not survive3. In fact, it is estimated that “almost 80% of global fish catches aredirectly or indirectly dependent on mangroves4”.

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Nanid (Esdepan Paulino) holding one of the mangrove crabs he caught in his family crab pots in Micronesia.  Photo Credit: © Nick Hall

Mangroves also provide ideal locations for aquaculture, which is currently “the fastest growing food-producing sector in the world5”, though often mangrove forests are destroyed for this purpose. There are movements in place to encourage more sustainable forms of aquaculture that complement the local environment instead of destroying it, but this is still not the norm. In addition to the more traditional fishery products, mangroves contribute to food security through the provision of several other food products, including honey, algae, fruit, salt, and leaves for livestock feed6.

In addition to their contribution to food security, mangroves also contribute significantly to local livelihoods, providing employment for a significant coastal population across the globe via the fisheries and tourism that they support. Mangroves also provide valuable timber for firewood and construction in local communities. Mangrove forests also provide water purification services and aid in the detoxification of wastes7. Aside from the more tangible benefits of these ecosystems, mangroves offer value that is much less easily quantified, in the form of aesthetics, culture, spirituality, and recreation.

Importantly, mangroves also provide significant buffering against coastal erosion, storm surge, and sea level rise. It is estimated that mangroves help to reduce wave heights by 31%8, protecting homes, property, and infrastructure from dangerous flooding. Additionally, these forests serve as incredible carbon storage mechanisms, thereby aiding in the preservation of human wellbeing via climate regulation.

Climate Mitigation

Mangrove forests serve a critical role in climate regulation and climate change mitigation. The trees/shrubs themselves, as well as the soil beneath them, serve as highly effective carbon sinks and storage sites. Mangroves absorb large amounts of carbon dioxide from the atmosphere during photosynthesis and are able to store this carbon, often referred to as “blue carbon,” for extended periods of time, in the plant structure and in the soil beneath them. Blue carbon, the carbon that is captured and stored in coastal ecosystems, can be locked away in the soils beneath mangroves for hundreds to thousands of years, if left undisturbed3.

Mangroves are incredibly efficient carbon sinks/stores, absorbing carbon at a much faster rate than terrestrial forests, and locking this carbon away for a much longer period of time. It is estimated that mangroves store 3 to 4 times more carbon than tropical forests9. Mangroves store much of their carbon in the soil and in their dead roots10.

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Photo credit: ©Ami Vitale

Notably, “Mangroves account for only approximately 1% (13.5 Gt year-1) of carbon sequestration by the world’s forests, but as coastal habitats they account for 14% of carbon sequestration by the global ocean11.”

While mangroves hold a great deal more carbon per area than terrestrial forests, they occupy only a fraction of the area, leading to much lower carbon sequestration totals compared to these terrestrial ecosystems. Despite their small areal extent, mangroves are still incredibly effective and important carbon stores, and their destruction presents a serious threat to efforts to mitigate climate change. The carbon emission potential of mangrove forests far exceeds their carbon sequestration rate, meaning that destroying existing mangroves releases far more carbon dioxide back to the atmosphere than can be counteracted by mangrove carbon sequestration12. This means that mangrove conservation is critical in our fight against climate change. While mangrove restoration is valuable and should continue to be explored as part of ecosystem-based adaptation projects, a focus on conservation of existing mangroves will prove much more effective in mitigating climate change.

It is also important to note that as climate change progresses, sea level rise will lead to the loss of more mangrove forests across the globe, leading to increased carbon emissions to the ocean and atmosphere as these forests are destroyed, and thus further exacerbation of climate change. This self-reinforcing loop presents a serious threat to mangrove forests. 

Climate Adaptation

Mangroves offer significant potential for aiding coastal communities in adapting to climate change. Climate change poses a serious threat to coastal communities and their livelihoods. Sea level rise, coastal erosion (due to storm surge and sea level rise), and more intense and frequent storms and heavy rainfall events are all expected impacts of climate change, and these impacts are already being documented in some areas13, 14. As these threats are looming, coastal populations are also expanding, and much of this growth is taking place in highly impoverished tropical nations15. As coastal vulnerability increases, it is crucial that climate adaptation and risk reduction measures be put in place. Mangroves may play an important role in climate adaptation in coastal communities.

Mangrove forests offer significant protection from coastal erosion, storm surge, and sea level rise, all of which may lead to potentially devastating and life-threatening flooding along the coast. Mangroves are already being utilized in some ecosystem-based adaptation (EBA) projects, which seek to use nature to promote resilience to climate impacts16. The restoration of mangrove forests in vulnerable areas can help to provide protection against climate threats, and can bolster food and livelihood security, both of which are threatened by climate change.

Biodiversity

Mangroves are critical ecosystems for promoting and supporting biodiversity. The unique role of the mangrove forest as the interface between coastal and terrestrial ecosystems enables it to provide a wide array of habitats and thus support a huge diversity of species, including terrestrial, estuarine, and marine organisms17. Mangroves support a large number of threatened and endangered species, such as the hawksbill turtle, the Bengal tiger, and several waterbird species, for example17, 18. Mangroves are also key habitats for many migratory birds that rely on the forests as stop-overs along their migratory paths. It has also been documented that mangroves provide refuge for corals from ocean acidification, thus contributing to the survival of these important species18.

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Crab-eating raccoon on Piscina Los Juanes, in the vicinity of Morrocoy National Park along the Caribbean Sea of Venezuela. Photo credit: ©Mark Godfrey/TNC

In addition to the vast array of life that mangrove forests directly support, they also contribute to the survival of other nearby ecosystems through their sediment trapping and filtration processes. Mangroves therefore indirectly support the species to which these adjacent ecosystems provide a home18. It has also been documented that mangroves may provide protection to corals from rising sea temperatures as a result of climate change. Warmer ocean waters can lead to deadly bleaching of corals, which also leads to the death of the organisms that live within and depend upon coral reefs19. Mangroves may prove to be very beneficial in protecting coral biodiversity and their dependent species, through the provision of shade and a buffer against rising ocean acidity20. Mangroves themselves are also a diverse group of organisms, with approximately 70 species documented worldwide21.

References

  1. The Nature Conservancy. Ecosystem Services. Mapping Ocean Wealth. Accessed on February 14, 2017. http://oceanwealth.org/ecosystem-services/.
  2. Munang, R. et al (2013). Using Ecosystem-Based Adaptation Actions to Tackle Food Insecurity. Environment 55(1), 29-35.
  3. Van Lavieren, H. et al (2012). Policy Brief: Securing the Future of Mangroves. Available at: http://unesdoc.unesco.org/images/0021/002192/219248e.pdf.
  4. Pidgeon, Emily (2010). Sequestration of Carbon Along Our Coasts: Important Sinks and Sources. Available at: https://www.cbd.int/cooperation/pavilion/cancun-presentations/2010-12-1-Pidgeon-en.pdf.
  5. Lehane, S. (2013). Fish for the Future: Aquaculture and Food Security. Future Directions International. Accessed on November 15, 2016. http://www.futuredirections.org.au/publication/fish-for-the-future-aquaculture-and-food-security/.
  6. Forestry and Food Security. FAO Corporate Document Repository. Accessed on February 14, 2017. http://www.fao.org/docrep/t0178e/T0178E06.htm.
  7. Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-Being: Wetlands and Water Synthesis. World Resources Institute, Washington, DC.
  8. Narayan S. et al (2016). The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences. PLoS ONE 11(5).
  9. Donato, D. et al (2011). Mangroves among the most carbon-rich forests in the tropics. Geosci. 4, 293–297.
  10. Alongi, D (2012). Carbon sequestration in mangrove forests. Carbon Management 3(3), 313-322.
  11. Alongi, D (2012). Carbon sequestration in mangrove forests. Carbon Management 3(3), 313-322.
  12. Mangrove Action Project. Climate Change. Accessed on November 15, 2016. http://mangroveactionproject.org/climate-change/.
  13. Mangroves can help us adapt to climate change. Samoa Observer (2013). Available at: http://www.pacificdisaster.net/pdnadmin/data/original/WSM_2013_Mangroves_help.pdf.
  14. IPCC (2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R. and L. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
  15. Neumann, B., Vafeidis, A., Zimmermann, J., and R. Nicholls (2015). Future Coastal Population Growth and Exposure to Sea-Level Rise and Coastal Flooding – A Global Assessment. PLoS ONE 10(3).
  16. Conservation International. Ecosystem-Based Adaptation in the Philippines. Accessed on November 15, 2016. http://www.conservation.org/projects/Pages/Using-ecosystem-based-adaptation-to-build-resilience-in-the-Philippines.aspx.
  17. UNEP-WCMC. Mangrove. Biodiversity A-Z. Available at: http://biodiversitya-z.org/content/mangrove–2.pdf.
  18. UNEP (2016). Mangrove conservation and restoration. Coastal Ecosystem-Based Adaptation. Accessed on November 15, 2016. http://web.unep.org/coastal-eba/content/mangrove-conservation-and-restoration.
  19. Greenwood, V. (2015). To Save Coral Reefs, First Save the Mangroves. National Geographic. Accessed on November 15, 2016. http://news.nationalgeographic.com/news/2015/02/150210-mangrove-protect-coral-bleaching-science/.
  20. USGS (2014). Mangroves Protecting Corals from Climate Change. Accessed on February 14, 2017. https://www2.usgs.gov/blogs/features/usgs_top_story/mangroves-protecting-corals-from-climate-change/.
  21. The Ocean Portal Team. Mangroves. Ocean Portal: Smithsonian National Museum of Natural History. Accessed on February 14, 2017. http://ocean.si.edu/mangroves.