© Ami Vitale

Mangroves

These forests, found where the ocean meets land and sea water meets fresh water, provide a wealth of benefits for people but are losing their rightful place in nature.

A primer on mangroves

Mangroves are trees or shrubs that are found in the intertidal zone of coastlines, or that area between the coastal environment and the terrestrial environment. These florae are well-adapted to living in saline (salty) and brackish environments, which is one of the reasons that they are so unique. There are about 80 species of mangroves found along tropical and sub-tropical coastlines, with a particularly heavy presence in Asia, followed by Africa and South America. The largest area of mangroves are found in Indonesia, followed by Brazil, Australia, Nigeria, and Mexico.

Mangrove trees are equipped with impressive filtration systems that allow them to filter out or exclude salt altogether, despite their twice-daily inundation by saltwater due to changing tides. Perhaps their most notable feature, mangroves have complex root systems that extend above and below the water line. These roots allow mangroves to stabilize themselves and prevent erosion to the coastline, and also provide habitat, nurseries, and feeding grounds for a vast array of fish and other organisms.

Benefits & Threats

Mangrove forests are among the most productive ecosystems on earth, and serve many important functions, including water filtration, prevention of coastal erosion, coastal protection from storms, carbon storage, food, timber, and livelihood provision, and biodiversity protection, among others. It is estimated that mangrove ecosystem services are worth US$33-57 thousand per hectare per year to the national economies of developing countries that host mangroves.

Despite the incredible value that these ecosystems provide, mangrove forests are continuing to be destroyed and degraded at a rate of about 1% per year as a result of land use change, exploitation, coastal development and climate change. At this rate, mangroves may all but functionally disappear by the year 2100 unless we take action now to protect and restore them.

Threats

Salinity and Sedimentation

Dams, irrigation and other alterations to landscape can alter the water, salinity and sedimentation levels of mangrove ecosystems which can contribute to mangrove decline.

climate change

Dams, irrigation and other alterations to landscape can alter the water, salinity and sedimentation levels of mangrove ecosystems which can contribute to mangrove decline.

overfishing / overharvesting

Mangroves are at high risk from unsustainable practices like overfishing and over-harvesting, leading to their destruction.

agriculture

Mangroves are often cleared away to make room for agriculture, often for palm oil plantations and rice paddies, two crops that were responsible for 38% of mangrove loss from 2000 to 2012.

Coastal development

As coastal populations continue to grow and coastal tourism increases, mangroves are cleared to make way for infrastructure, businesses, hotels, and homes.

aquaculture

To meet the world’s growing demand for seafood at a time when overfishing has led to smaller catches, aquaculture, which is the process of farming seafood, has emerged as the fastest growing food sector.

Pollution

More people are living along coasts than ever before and consequently pollution runoff has risen, threatening nearby mangroves which act as natural filters of runoff to the ocean.

Benefits

Improved Fisheries/Fish Production:

Mangroves serve as a nursery ground for many species of juvenile fish, including some commercially important species, thus contributing to food security, local livelihood sustainability and biodiversity.

INCREASED HUMAN WELLBEING

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

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.

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.

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.

Improved Fisheries / Fish Production

Mangroves serve as a nursery ground for many species of juvenile fish, crustaceans, mollusks, and more. These ecosystems are particularly important for reef fish.

It is estimated that up to half of local fish catches are in some way dependent on mangroves. Some of these are commercially important species, thus contributing to food security, local livelihood sustainability and biodiversity.

Atlantic spadefish (Chaetodipterus faber) amongst the roots of red mangrove trees (Rhizophora mangle) in the Belize Cays, Suna Tunicate Cove, Belize. © naturepl.com / Tim Laman / WWF

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 species, without which many fisheries, including local coastal fisheries as well as commercial coastal and offshore fisheries, would not survive. In fact, it is estimated that “almost 80% of global fish catches are directly or indirectly dependent on mangroves”. Mangroves also provide ideal locations for aquaculture, which is currently “the fastest growing food-producing sector in the world”, 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 feed.

Searching for mud crabs in the mangroves in Kei Kecil, Indonesia. © WWF-US / James Morgan

 

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 wastes. 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%, 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 undisturbed.

 

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 forests. Mangroves store much of their carbon in the soil and in their dead roots.

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 ocean.”

WWF, with support from players of People's Postcode Lottery, is working with communities in coastal Kenya to protect marine turtles. © Jonathan Caramanus / Green Renaissance / WWF-UK


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 sequestration. 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 areas. As these threats are looming, coastal populations are also expanding, and much of this growth is taking place in highly impoverished tropical nations. 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.

Mangroves at Baie D'Ambodi-Vahibe (west-inner), a survey site on the CI Marine RAP (Rapid Assessment Program) expedition to northeast Madagascar, March 2006, Africa. © CI/ photo by Sterling Zumbrunn


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 impacts. 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 organisms. Mangroves support a large number of threatened and endangered species, such as the hawksbill turtle, the Bengal tiger, and several waterbird species, for example. 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 species.

 

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 home. 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 reefs. 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 acidity. Mangroves themselves are also a diverse group of organisms, with approximately 70 species documented worldwide.

Laurens Takati colecting mud crabs from the mangrove area around his village. Kei Kecil, Malukus, Indonesia. © WWF-US / James Morgan

Agriculture

Mangroves are often cleared away to make room for agriculture, often for palm oil plantations and rice paddies, two crops that were responsible for 38% of mangrove loss from 2000 to 2012. The industry has seen enormous growth in the last few decades and shows no signs of slowing down. Palm oil is projected to increase by 256 million tons by 2050 which will require 53 million hectares of land, some of which will likely encroach on mangroves. Palm oil is nearly ubiquitous in the commercial food industry, found in products such as pizza dough, cookies and soda, as well as detergents and other products.

 

Indonesia and Malaysia, two countries abundant in mangroves, are responsible for 85% of the world’s palm oil production. The two countries have promoted the industry and resist regulation because of its contributions economically and to national energy security. Indonesia plans to expand palm oil into the Papau province in the coming years which will likely threaten mangroves there.

 

Mangroves are also indirectly affected by the agriculture industry, affected by the chemicals and fertilizers used in on plantations that runoff into the environment. In addition, water may be diverted for crops, through dams and irrigation, which may change the salinity or amount of water in mangrove habitats.

Aqualture

To meet the world’s growing demand for seafood at a time when overfishing has led to smaller catches, aquaculture, which is the process of farming seafood, has emerged as the fastest growing food sector. It has also become the number one cause for mangrove deforestation.

 

The world’s production of shrimp has risen significantly over the last two decades, thanks to aquaculture and globalization. Most of the shrimp is farmed in southeast Asia where 90% of the world’s aquaculture industry is located and where 70% of Indonesia’s 3.7 million hectares of mangroves are damaged or degraded by aquaculture.

 

Mangroves are considered by many to be more valuable than shrimp farms. A 2006 study by the United Nations Environment Program puts the annual value of mangroves between $2,000 and $9,000 per hectare, though some estimates are much higher and in total, the annual loss due to aquaculture is between $3.78 billion and $17.01 billion. Governments and coastal communities are working toward protecting and replanting mangroves, and farmers are using techniques like conserving mangroves in the center of their shrimp farms.

Aerial view of shrimp ponds carved out of mangrove forest in the Sarawak Mangrove Reserve area, Sarawak, Borneo, Malaysia. June 2006. Several shrimp ponds have been abandoned. © naturepl.com / Tim Laman / WWF

Converting mangroves to aquaculture releases a lot of carbon dioxide as well. The annual increase in blue carbon emissions, or carbon stored in coastal and marine ecosystems, is about 112 tons to 392 tons per hectare while the potential loss of blue carbon stock from converting mangroves to shrimp farms ranges from 661 tons to 1,135 tons per hectare.

Fertilizers, waste and antibiotics are used in the farming process and can negatively impact human health when shrimp is consumed and damage surrounding mangroves. Sometimes farmers abandon their shrimp farms because of the pollution, so farmers move on and cut down more mangroves, while many abandoned shrimp farms don’t revert back.

Pollution

More people are living along coasts than ever before and consequently pollution runoff has risen, threatening nearby mangroves which act as natural filters of runoff to the ocean. Pollution may come from sources like urban runoff, agriculture and oil spills and can interfere with the exchange between mangrove roots and the atmosphere and soil. Oil can, for example, suffocate mangroves by coating their roots.

 

An overabundance of nutrients like potassium and nitrogen from urban runoff can disturb mangrove growth. In Mumbai, high concentrations of lead, mercury and chromium have been found, in addition to debris dumping and untreated sewage water. The pollution load varies for different mangrove forests as well as among species. For example, Avicinnea is one of the most tolerant species to heavy metals.  In India, the A. marina has increased in numbers, likely due to its resistance to pollution, thus causing a decline in biodiversity.

Salinity and Sedimentation

Dams, irrigation and other alterations to landscape can alter the water, salinity and sedimentation levels of mangrove ecosystems which can contribute to mangrove decline. A new causeway, for example, may impede the tide coming into the mangroves, lowering the fresh to saltwater balance of the estuary. On the other hand, irrigation or a newly constructed dam may alter freshwater flow into the mangroves, increasing its salinity.

 

While mangroves have various adaptation techniques to deal with salinity, such as filtering at the root level or storing excess salt in leaves and shedding them, high salinity can cause dehydration, imbalances in nutrition and changes in iron levels that can negatively impact mangroves.

 

A moderate amount of sedimentation is beneficial for mangroves, bringing nutrients from upstream areas and increasing the amount of soil that the mangroves grow on, a process known as accretion. High sedimentation rates exceeding 1 cm/year can be caused by upstream deforestation and can slow growth or smother mangroves. In Kenya, 100 hectares of mangroves were lost due to dredged up sediment from an infrastructure project. Too much sediment can smother the mangroves, blocking the exchange of oxygen between the roots, soil and atmosphere which can cause root damage or oxygen deficiency. Pneumatophores are the famous  vertically spiked roots in some species of mangroves and may be covered by water which would cause the mangrove to perish while the species rhizophora are less likely to be covered by water because the roots are stilted and are less likely to be sufficiently covered.

Climate Change

Climate change is just one of the many threats that mangroves must respond to, and the risk looms larger all the time, as carbon dioxide concentrations increase and global temperatures continue to rise. Climate change will lead to the degradation or destruction of mangroves as a result of sea level rise (the greatest threat to mangroves), changing precipitation patterns, higher temperatures, and stronger, more frequent storms.

 

It is estimated that 29% of mangroves will be lost due to sea level rise alone, given a 1 meter sea level rise by the year 2100 (Blankespoor et al. 2017). Ironically, mangroves help to defend the coastline from sea level rise and have their own mechanisms for adapting to a changing sea level. However, they may not be able to keep pace with the rate of sea level rise brought on by climate change, thereby leading to their demise.

 

Climate change will also lead to the destruction of coral reefs, which protect mangroves from wave action and have a symbiotic relationship with mangrove forests. The destruction of coral reefs will further harm mangroves, and vice versa, leading to reduced coastal protection and significant loss of biodiversity. Without mangroves, climate change impacts will be greater and more destructive for coastal communities, who currently rely on mangrove forests for protection from storms, sources of food, and livelihood sustainability. The world can expect to see more climate-related deaths because of mangrove loss.

Coastal Development

One of the biggest threats to remaining mangrove forests is coastal development. As coastal populations continue to grow and coastal tourism increases, mangroves are cleared to make way for infrastructure, businesses, hotels, and homes. Development in the coastal zone also leads to mangrove destruction indirectly through the increased pollution, altered hydrology, and harmful human contact that can result. Additionally, coastal development too close to mangrove habitat can limit their ability to migrate landward as sea levels rise, diminishing their resilience and therefore the resilience of the communities that they protect. Ironically, destruction of mangroves for development puts the new construction at even higher risk to damage from storms, leading to increased economic losses.

 

Tourism is one of the major factors leading to increased coastal development, as people travel across the globe to experience exotic coastal destinations. Tourism is a welcome source of economic growth in the developing nations that host the majority of mangrove forests. However, tourism can be very destructive, as mangroves are cut down to create a better “ocean view” or to build airports, marinas, golf courses, resorts, and other tourist attractions. Sadly, despite the promise of growth and wealth from these incoming entrepreneurs, it is often the case that the local community does not benefit at all from the profits. In this way, they are left out of the burgeoning tourist economy that has also destroyed their former means of livelihood sustainability – mangroves. Without the mangrove fisheries that support many coastal populations, and the food and fuel that mangroves provide, families are forced to migrate elsewhere in search of a place that can sustain them.

 

Coastal development can be sustainable, however, if it is well-planned, innovative, and integrates the surrounding ecosystems, livelihoods, and needs of all stakeholders. Ecotourism and integrated coastal zone management offer promising opportunities for future development.

© Diego M. Garces / WWF

Overfishing / Overharvesting

At first glance, the twisted roots and swamp-like environment of the mangrove forest may not appear to be one of abundance, but, in fact, mangroves are one of the most biodiverse, valuable ecosystems on the planet. These productive ecosystems serve as valuable resources for coastal communities, providing sources of food, medicine, firewood, and income. However, as with any natural resource, mangroves are at high risk from unsustainable practices, including overfishing and over-harvesting, both of which are leading to their destruction and degradation across the globe. Why are mangrove resources being exploited? There are several reasons, which include an ever-increasing global and coastal population which creates higher demand, an increase in poverty levels, globalization of industry (which means that locals must compete with commercial demands for the same resources), and increased coastal tourism.

 

In addition to these pressures on mangrove resources, many coastal areas lack effective coastal resource management structures and governance to enforce these structures. Often, these areas simply do not have the man-power or the resources to effectively manage the coastal zone. However, effective coastal management that includes all stakeholders is a necessity if we are to prevent further suffering by local populations and further destruction of mangroves. The current state of exploitation leads to food insecurity, livelihood insecurity, and increased conflict among local populations – in other words, a highly unsustainable state. Alternative livelihood options, sustainable tourism, fisheries management, and education can all effectively reduce overuse and lead to positive development outcomes, including reduced poverty, enhanced food security, less conflict, and healthier mangrove ecosystems.