By Evangeline Wilby
Mangroves are one of the most biologically diverse and ecologically productive ecosystems on earth. They are found in salt water coastal regions and provide a range of critical ecoservices that must be protected. Mangrove systems are very important carbon sinks, since they have the ability to sequester vast amounts of carbon, even more than terrestrial forests.1 They are therefore essential in helping to mitigate climate change by removing carbon dioxide from the atmosphere and helping to prevent the multitude of effects from global warming.
In addition, mangroves act as storm defences, which are particularly useful in areas exposed to extreme weather patterns, which are made worse by climate change. For coastal communities that are particularly vulnerable to flooding, storm activity and tropical cyclones, mangroves offer essential protection, as they significantly reduce wave height. Here, there is an economic trade-off, as when mangroves are removed, the timber from them has economic value. However, the economic cost of storm damage is far greater than the economic gain of their timber, so in the long term, conserving the mangroves will pay greater dividends to the local community.2 One study in central America found that hurricanes lead to significant losses in economic activity in the short term and that mangroves are capable of preventing these devasting effects, but it is likely only large-scale conservation efforts will be able to provide protection, so conservation strategies should consider how to protect mangroves on large, connected scales.3
Mangroves are also nurseries for many species, and the complex three-dimensional space within mangroves provides an array of niches, with wide food availability, high productivity and protection from predators and currents. Fish and shrimp are particularly attracted to these habitats in their early life stages due to the cool refugia and higher oxygen content they provide. Mangroves harbour many bacterial species and tree detritus, cycling many nutrients and food resources for juveniles, showing that biotic interactions within these systems are critical to preserve, to allow ecosystem functioning. Moreover, mangroves host numerous critically endangered species, highlighting their need for conservation, such as the rainbow parrot fish and the overexploited goliath grouper, which depend on this system to complete their life cycle.4
For humans, mangroves provide a source of food and employment for fishing communities, particularly in fish-protein dependent nations, when used in a sustainable manner. One study estimates that there are 4.1 million mangrove associated fisheries globally. This shows the scale of their importance to people’s livelihoods, with the study highlighting key areas where mangrove fisheries were of high use such as Indonesia, India, Bangladesh, Myanmar, and Brazil. Therefore, mangroves are not just ecologically important, they are also economically important.5
However, their importance may be going unrecognised, as 35% of the world’s mangroves have been lost since 1980. They are heavily threatened by climate change, which is causing sea level rise, leading to loss of the mangroves. Further threats include coastal development, pollution, population growth and human exploitation. In particular, unsustainable aquaculture such as shrimp farming is a driver of mangrove loss.6 The creation of shrimp farms within mangrove ecosystems alters the hydrology and salinity and can introduce non-native species and therefore disease. Moreover, chemicals and medicines used within fish farming can further pollute the ecosystem.7
Solutions to these problems involve interdisciplinary approaches, encompassing science, policy, and partnerships. For example, blue carbon initiatives aim to provide high-quality scientific data on marine systems and how they can be used in carbon sequestration and mitigating climate change. This data provides useful tools for better understanding these threatened ecosystems, how they function as a whole and how to conserve them. Many non-government organisation (NGOs) focus on these relationships to develop frameworks for better management on national and, crucially, international scales.6
This scientific information can then be linked to policy, a key step in conservation of habitats. This allows blue carbon initiatives to be included in agreements and frameworks, to put the scientific theory into practice.6 For example, policy to position shrimp farms behind mangroves can prevent damage but needs effect enforcement and incentives to be successful7. The use of partnerships and community-based projects to move towards mangrove-friendly aquaculture will be essential in finding holistic, realistic, and implementable solutions, ensuring both environmental sustainability, but also employment protection and food security, which ethically, must all be protected as best as possible.
Mangrove restoration projects are also used where mangrove seedlings are planted in greenhouses and then transferred to ocean mudflats, to try and replenish lost habitat. However, this isn’t always a simple or suitable solution, since once the mangroves are removed, the base layer of habitat often becomes eroded and reshaped and is not suitable for regrowth.8 Far more research is needed into the viability of mangrove restoration in order to not waste conservation resources and use them optimally.
Raising awareness for the important services mangroves provide and integrating this understanding with scientific data and political will, can be used to move towards conserving mangrove’s ecosystem services so that future generations who will be dependent on them, can benefit from them.
References:
- Fatoyinbo T, Feliciano EA, Lagomasino D, Lee SK, Trettin C. Estimating mangrove aboveground biomass from airborne LiDAR data: a case study from the Zambezi River delta. Environmental research letters; Environ.Res.Lett. 2017; 13 (2): 10.1088/1748-9326/aa9f03.
- Balmford A, Bruner A, Munro K, Myers N, Naeem S, Paavola J, et al. Economic Reasons for Conserving Wild Nature. Science (American Association for the Advancement of Science); Science. 2002; 297 (5583): 950-953. 10.1126/science.1073947.
- Del Valle A, Eriksson M, Ishizawa OA, Miranda JJ. Mangroves protect coastal economic activity from hurricanes. Proceedings of the National Academy of Sciences – PNAS; Proc Natl Acad Sci U S A. 2020; 117 (1): 265-270. 10.1073/pnas.1911617116.
- IUCN. Juliet Blum and Dorothée Herr Mangroves: nurseries for the world’s seafood supply. 2017. Available from: https://www.iucn.org/news/forests/201708/mangroves-nurseries-world%E2%80%99s-seafood-supply. [Accessed 3rd February 2022]
- Zu Ermgassen, Philine S. E, Mukherjee N, Worthington TA, Acosta A, Rocha Araujo A,Rosa da, Beitl CM, et al. Fishers who rely on mangroves: Modelling and mapping the global intensity of mangrove-associated fisheries. Estuarine, Coastal and Shelf Science. 2020; 247 106975. 10.1016/j.ecss.2020.106975.
- Conservation International. Mangroves: protecting and restoring quite possibly the most important ecosystem on earth. Nd. Available from: https://www.conservation.org/priorities/mangroves [Accessed 3rd February 2022]
- Ashton, Elizabeth, The impact of shrimp farming on mangrove ecosystems. Cab Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources. 2010; 3. 10.1079/PAVSNNR20083003
- Ellison AM. Mangrove Restoration: Do We Know Enough? Restoration Ecology; Restoration Ecology. 2000; 8 (3): 219-229. 10.1046/j.1526-100x.2000.80033.x.
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