Supervised by: Joanna Rhodes MChem DPhil MRSC Solicitor. Joanna studied her undergraduate degree in Chemistry at St Catherine’s College, Oxford during which she was awarded the Unilever Prize in Practical Chemistry. Her D.Phil at St John’s College, Oxford, was taken in Professor Richard Compton’s Electrochemistry Group where she published numerous research papers in the area of Electroanalytical chemistry as well as two chapters for the Wiley Encyclopaedia of Electrochemistry. She has an interest in sustainability and building a better future.
Abstract
As the importance of ocean ecosystems in regulating climate change has become better understood, the attention of scientists has been drawn to vegetated coastal ecosystems capable of sequestering huge volumes of carbon. Mangroves are an example of such a vegetated coastal ecosystem and, until relatively recently, this ecosystem was poorly researched and little understood. The scale of the ability of mangroves to sequester carbon dioxide is only now being fully recognized, while mangrove forests teeter on the brink of becoming carbon sources due to extensive deforestation.
As well as sequestering blue carbon, mangroves provide nurseries for thousands of fish species and serve as both habitat and food source for an entire ecosystem of plant and animal species. Mangrove forests act as physical buffers to natural disasters, protecting coastlines from the harsh impacts of tsunamis and intercepting floods. With urban growth and intensive aquaculture expansion, the threats to mangroves continue to increase. The territory occupied by mangrove forests provides the ideal environment for shrimp farms, and deforestation of mangroves has occurred to make space for this lucrative but unstable industry.
Farmers and the local population have been encouraged to preserve mangrove forests since 2015, when regulations were imposed in Southeast Asia in order to control deforestation. However, the conservation of mangroves is complicated by competing interests and several constraints. Although mangroves can provide economic output for governments if they are managed wisely and sustainably, Southeast Asian nations are still learning how to use mangroves to generate tourism and incorporate inter-farming into mangroves. Legislation has been shown to work only when the stakeholders each have a clear understanding and derive a benefit from the scheme, so bottom-up aid works more effectively than a top-down approach when it comes to adapting to the community’s needs.
This article aims to illustrate the role of mangrove forests in the carbon cycle and their impact on climate change, as well as how their protection and restoration may benefit entire communities and economies.
Introduction
As the importance of ocean ecosystems in regulating climate change has become better understood, the attention of scientists has been drawn to vegetated coastal ecosystems capable of sequestering huge volumes of carbon. Mangroves are an example of such a vegetated coastal ecosystem and, until relatively recently, this ecosystem was poorly researched and little understood. The scale of the ability of mangroves to sequester carbon dioxide is only now being fully recognized, while mangrove forests teeter on the brink of becoming carbon sources due to extensive deforestation.
As well as sequestering blue carbon, mangroves provide nurseries for thousands of fish species and serve as both habitat and food source for an entire ecosystem of plant and animal species. Mangrove forests act as physical buffers to natural disasters, protecting coastlines from the harsh impacts of tsunamis and intercepting floods. With urban growth and intensive aquaculture expansion, the threats to mangroves continue to increase. The territory occupied by mangrove forests provides the ideal environment for shrimp farms, and deforestation of mangroves has occurred to make space for this lucrative but unstable industry.
Farmers and the local population have been encouraged to preserve mangrove forests since 2015, when regulations were imposed in Southeast Asia in order to control deforestation. However, the conservation of mangroves is complicated by competing interests and several constraints. Although mangroves can provide economic output for governments if they are managed wisely and sustainably, Southeast Asian nations are still learning how to use mangroves to generate tourism and incorporate inter-farming into mangroves. Legislation has been shown to work only when the stakeholders each have a clear understanding and derive a benefit from the scheme, so bottom-up aid works more effectively than a top-down approach when it comes to adapting to the community’s needs.
This article aims to illustrate the role of mangrove forests in the carbon cycle and their impact on climate change, as well as how their protection and restoration may benefit entire communities and economies.
The Mangrove Ecosystem
Mangroves are recognized for the many important ecological services they perform (1). These include protecting the well-being of all living organisms in the regions they occupy and providing nurseries for thousands of different species of fish. Many animals that dwell in mangrove habitats depend on these as their primary food source (1). Certain fish species living in these mangroves are also economically important for humans in the fish market. However, human activities, such as the rapid development of aquaculture and agriculture, threaten these habitats.
Southeast Asia is home to the largest and most diverse mangroves, with over 19% of the global area of mangroves located in Indonesia, making it the country with the highest extent of mangrove forest (2). Indonesian mangroves protect beaches from sea abrasion and provide nurseries and breeding grounds for many important marine species (3). In many Southeast Asian regions, mangroves are home to some of the world’s most economically important marine species, providing food for both humans and other wildlife, such as certain species of birds and monkeys (4).
The mangroves of the Pacific coast of Southeast Asia have high levels of rain and steep slopes, along with streams that carry a significant sediment load (5). Marine Life on the Pacific coast of Southeast Asia is positively and negatively affected by this terrain and climate. For example, the fresh sediment flowing into the mangroves can cause the death of mangrove trees, as the sediment could lead to root smothering (5). Sediment could also clog up the filter-feeding apparatus of small marine animals living on the mangroves, causing them to die (6). Sediment can clog fish gills and lower the growth rates of the plants and animals in the mangroves. However, sediment can also function as a long-term sink for carbon and stormwater contaminants, supporting biodiversity (6).
The role of mangrove forests in the carbon cycle and their impact on climate change
The importance of curbing greenhouse gas emissions cannot be overstated. As outlined in the Paris agreement, temperature increases must be limited to 1.5 Celsius to allow for a habitable planet (7). Sequestration of blue carbon in vegetated coastal habitats such as mangrove forests is crucial to achieving this goal. Mangroves live in brackish water along the coasts of tropical and subtropical areas; they are the only trees able to live in saltwater and have adapted to excrete salt from their leaves (8). Their tangled, nest-like roots are very recognizable and allow the trees to remain upright despite flooding waters (8). Though carbon sequestration is more commonly associated with terrestrial forests, mangroves can store up to four times the carbon of a tropical forest in the same space and are currently responsible for up to 6.2 billion tonnes of stored carbon (9). They act as highly efficient carbon sinks, covering only 0.4% of the forested regions (10).
Mangroves owe a substantial portion of their carbon sequestration efficiency to the soil. Aside from the vegetation sequestering carbon, the root systems of the mangrove trees store allochthonous organic material above meters of carbon-rich peat (10). Anaerobic sediment also contributes to the high carbon storage of mangrove ecosystems (11). The tidal flooding of the mangroves keeps the soil saturated or submerged under water, preventing microbial activity and allowing for carbon accumulation (12). All told, the soil of the mangrove forests accounts for 49-98% of the carbon they store (13).
Beyond preserving these mangroves for persistent carbon storage, it must be recognized that as more mangroves are being damaged or destroyed by human activity and development, these mangrove ecosystems will become huge carbon emitters. Deforestation and land use change currently account for 8-20% of human-driven carbon dioxide emissions (3). For the same reason that they are so valuable in the fight to curb greenhouse gas emissions, the mangroves also emit far more carbon dioxide than terrestrial forests, along with a considerable amount of methane, a potent greenhouse gas, when destroyed. Though mangroves only make up 0.7% of tropical forests, they are responsible for 10% of emissions from tropical deforestation (9).
Threats to mangrove forests
Unfortunately, mangrove forests are in severe decline, decreasing by 30-50% in the past half-century (13). Human activity is the driving force behind this decline. While mangroves have long been deforested to be used for wood and to make medicine from the bark (1), approximately 62% of mangroves lost between 2000 and 2016 were caused by land use change, most notably for aquaculture and agriculture, as well as coastal development and urban area expansion (9). Shrimp farms are one of the biggest motivators behind this destruction, specifically in Thailand, and this particular threat is dealt with in more detail below. Besides aquaculture, palm and rice are the next most prominent contributors to mangrove deforestation, especially in Myanmar, Indonesia, and Malaysia (14).
The sea level rise that mangroves are crucial to preventing could, unfortunately, pose a further threat to the mangroves themselves (15). Overflooding of the mangroves and sediment disruption threaten the ecosystem, and the spike in wind and wave activity may result in erosion. This would release accumulated carbon into the water (15). Another anthropogenic impact on coastal ecosystems is a modification to the sediment accumulation of the mangroves. River dams prevent the natural movement of silt and sediment that accrete to keep pace with sea level rises and store carbon (15).
A multiplier effect takes place when mangroves are deforested. The carbon sink becomes a carbon source contributing to climate change due to carbon dioxide and methane emissions. Loss of biodiversity causes frequent disease outbreaks in ponds leading to the use of antibiotics, fertilizers, disinfectants, and pesticides for aquaculture. These cause serious problems, as they are usually released into streams of water that end up in the sea without being treated, harming coastal fishing communities and decimating coastal oyster populations (18). In December 2004, when they were intact, the mangroves acted as a physical barrier against an Indian Ocean tsunami, protecting the coast from Sri Lanka to Thailand. Thai populations regretted that they had lost so many mangroves when they recognised such benefits for them (18).
Shrimp farming as a specific threat to mangrove forests
Between 1976 and 1991, 56-65% of lost Thai mangroves were caused by conversion of land to shrimp farms (9). Mangroves provide an ideal environment for shrimp farming due to the nutrient-rich soils they have that nourish the warm water with an ideal pH and salinity for shrimp farming conditions (17). Shrimp farms and other forms of aquaculture also require large amounts of water. In Southeast Asian developing countries, such as Thailand and Indonesia, it can be prohibitively expensive to acquire significant volumes of potable water, prompting the use of mangrove swamp water (17). Aquaculture, such as shrimp or prawn farming, can be very profitable for the farmers and the countries exporting them while also providing plenty of jobs for local populations. So, from the 1970s, Thailand began to encourage intensive shrimp farming, ultimately becoming the world’s third-largest shrimp exporter. Under increased government pressure to make Thailand a large shrimp manufacturer, farmers in villages accepted low-paid cash jobs cutting mangroves for concessionaires or engaging in commercial fishing, having to cut down mangroves to get to the fish more efficiently (20). The environmental cost of the industry has been habitat loss for large amounts of marine life and the destruction of thousands of hectares of mangroves (18,19). Furthermore, with a lifespan of only five years, these shrimp farms leave acidic water and degraded soil in their wake, with the ability to store only 11% of the carbon a healthy mangrove would (9).
More recently, with demand for shrimp remaining high but the price being low, Thailand has been struggling to maintain its position as an exporting superpower of shrimp. Despite all their efforts, from moving shrimp to sweet water and trying to introduce a new species called the white shrimp, they have still failed to keep up. From an economic perspective, this may be an incentive for farmers to restore mangroves after they have been valued at 3.5 million dollars per sq. km per year, according to the United Nations Environment Programme (UNEP) (20).
Barriers to conservation and community projects
“We often refer to mangroves as the supermarket for the local people because, there, they have some building supplies, food supplies, shelter, and medicines. Therefore, people have been traditionally relying on the mangroves for all those things in the local fishing communities,” said Jim Enright, the Asia coordinator at the Mangrove Action Project (MAP), an NGO that advocates for the recovery of mangrove forests (18). Which invites the question: if mangroves are of such use to local populations, why aren’t they preserving or protecting them?
Education is possibly the answer, with commentators suggesting that local populations lack knowledge regarding the value of mangrove forests; they cut them down without realizing they are losing physical tsunami and flood amelioration, fish nurseries, and massive carbon sinks (20). Therefore, conservation projects educating local communities arguably have the potential to be the most successful. In such projects, communities receive support and education in a bottom-up approach to integrating mangrove preservation into their daily lives.
Throughout the years, there have been several bottom-up project attempts. For instance, the Marriott Spirit to Serve initiative has tried to support local communities by complying with sustainable seafood sources and local procurement practices. In partnership with IUCN and Mangroves for the Future (MFF) Thailand, Marriott created a community-based land use map and a sustainable management plan in order to create sustainable livelihood opportunities while restoring mangroves. This project developed an Integrated Coastal Management (ICM) network with ten communities in the Bang Kaew District, Samut Songkram. Toyota also established the Cheewa Panavet Biodiversity and Sustainability Learning Center in Ban Pho Plant in Thailand. This project is focused on raising awareness regarding coastal ecosystems and collecting garbage with volunteers to restore coastal habitats. There has even been an education center established, the Royal Thai Army Nature Education Center at Bangpu Mangrove, in collaboration with the Foundation for Environmental Education for Sustainable Development (Thailand). This center provides information and educational materials to local students.
With an increasing number of projects, more and more villagers are getting involved. The restoration of mangroves is now an opportunity for them to earn a profit from abandoned ponds and recover marine crops that have been lost, such as oysters or crabs. Local farmers can also turn ponds into natural polyculture systems while restoring mangroves. In this way, they can receive profit while having long-term food without artificial feeding. However, since these are relatively new projects and not all locals can see the direct benefits of mangrove replanting and protection, these initiatives may take a while to reach their full potential. (19).
The role of mangroves in coastal economies
It is difficult to adequately measure the financial impact of the mangrove ecosystem since it has such a wide variety of effects, from affecting a country’s GDP to dictating the livelihoods of its people. However, according to the World Conservation and Monitoring Centre, mangroves generate an astounding US$33,000-US$57,000 per hectare per year, solely off of the goods and services they provide (23). Around the world, more than 600 million people live in coastal environments, where many of these coastal inhabitants require marine species such as fish for both income and food. Mangrove ecosystems are essential as they help maintain a healthy level of fish stocks, with 95% of commercial fish species requiring mangrove roots and seagrass leaves within their life cycle (24). If the mangrove ecosystem is destroyed, many fish won’t have a safe habitat to reproduce and the population will decline rapidly.
In addition to having a significant financial role as producers, the mangrove ecosystem is also essential in natural disaster amelioration, acting as a natural barrier to protect shorelines from erosion. It has been determined that the mangrove ecosystem can reduce wave height by up to 66%. As a result of climate change, the frequency of severe storms has increased by 40%, making this a matter of rising significance (25).
Mangrove ecosystems are also a major tourist attraction which, when harnessed correctly, can also help to boost the economy of a country. Because they support coral reefs and the entire marine food web, blue carbon ecosystems also provide rewarding diving, snorkeling, and whale-watching experiences. A study by the World Tourism Organization showed that each year around the world, mangrove ecosystems raise about US$20 billion in tourism revenue, helping boost a country’s GDP (26). Ecotourism is defined as “responsible travel to natural areas that conserves the environment, sustains the wellbeing of local people, and involves interpretation and education” (28). Ecotourism can utilize the wide range of natural and cultural ecosystem services provided by mangroves to improve local livelihoods. This type of tourism comes in many forms, for instance, supplementary income from goods and services such as park user fees, tour guiding, and boat rental (29). Recreational activities include boat and boardwalk tours, kayaking, and wildlife watching, and may even involve participating in replanting efforts that directly help protect biodiversity and improve coastal sustainability (23).
However, despite the tourism opportunities that the mangrove ecosystems are able to bring, ecotourism must be implemented correctly in order to minimize the adverse impacts of tourists on local habitats. These impacts can be physical, including increased shoreline erosion, noise, and pollution, or social, including the exclusion of local tour operators and communities (22). It should also be noted that globally, tourism accounts for about 8% of greenhouse gas emissions (30).
The role of Legislation and other recommendations
Mangrove management falls between the cracks within national legislative systems designed to protect the environment because the legislative instruments were not drafted with consideration for the unique situation of mangrove forests (32). Mangroves blur the boundary between the sea and land, which means that the state authority over the mangrove system is complex and often falls under the forest sector (32). However, the policies regarding terrestrial forests are usually not appropriate for mangrove forests.
When responsibility for the mangroves falls under multiple sectors, there tends to be a lack of coordination between agencies with overlapping jurisdictions of the mangroves. This ambiguity does little to benefit regulations regarding mangroves (32). For example, in the Philippines, mangrove jurisdiction falls under the Department of Environment and Natural Resources and the Department of Agriculture. In Vietnam, jurisdiction also falls under two different government authorities; in Indonesia, mangrove jurisdiction falls under four (32). All of these places have shown a lack of coordination and collaboration when it comes to protecting mangrove forests (32).
The legislation that exists to protect mangroves is not properly enforced. There should be a mechanism for collaborative governance to ensure multi-level coordination, from community-based management to international organizations. These mechanisms are rare, and where they do exist, they are poorly implemented. Incentive structures have been cited as one of the causes behind this lack of coordination (31).
Considering the convoluted state of authority over mangroves, a possible solution is leaving the responsibility to local communities. They are often best suited to know social and ecological situations relevant to developing regulations. Since their livelihood depends on the mangroves, they have a vested interest in ensuring their protection (32). Overall, community-based programs that partnered with external NGOs or research facilities for technical assistance were more successful than “top-down” programs initiated by the central government (32).
While strict government regulation is necessary to protect the mangroves from criminal exploitation such as illegal deforestation, listening to local communities is crucial in ensuring the regulations are suitable. An increase in funding and attention to the mangrove forests would also be beneficial; lack of budget is a significant issue with inter-sectoral coordination committees (31, 32).
Conclusion
This research has demonstrated that mangroves play a pivotal role in both the carbon cycle and the economy. The sediment accumulation of these ecosystems sequester millions of tons of carbon every year, mitigating climate change and the disastrous effects of anthropogenic CO2 emissions.
From local livelihood to infrastructure protection, mangrove forests can be worth billions to the modern economy. Revenue generated from tourism can be beneficial in multiple ways. While boosting economic benefits, ecotourism can also help bring attention to protecting the mangroves.
Despite these benefits, the importance of preserving mangrove forests is still widely overlooked, and the creation and implementation of enforceable regulations to conserve these ecosystems suffer from a lack of multi-level coordination. Top-down efforts are not suited to local needs, resulting in ineffective policies. Mangroves are still being destroyed at an alarming rate, primarily by the shrimp farming industry, and the exploitation of this land is not easily reversible. While both restoration and conservation of mangrove forests are being looked at to offset carbon emissions, conservation will have a significantly greater impact (9). Even after biomass recovery of the mangroves, it is not clear that the carbon stocks will be restored, especially not on a short timescale (16). Investment in multiple generations of regeneration would be required to fully rehabilitate these fragile, beautiful and essential ecosystems.
Given the difficulty in regenerating or reversing the damage to deforested mangroves, we conclude that protecting the remaining undamaged mangroves from any further deforestation should be prioritized to mitigate climate change and conserve the biodiversity in these habitats. However, existing protected area networks cover only 6.9% of mangrove areas worldwide (17).
Our first recommendation is for urgent action to be taken to preserve and protect existing mangrove forests so these ecosystems can continue their role in mitigating climate change, protecting coastal ecosystems from extreme weather, and acting as a rich source of biodiversity.
Our second recommendation is for sources of funding to be provided that enable communities to invest in the generation-long regeneration and rehabilitation programs that would be necessary to convert deforested areas back into vibrant and thriving mangrove forests.
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