Threats to Mangroves

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Mangrove Science Database

Coastal Development

Coastal development may be the primary threat to mangroves. Not only are the forests lost when a coast is developed, but a man-made structure almost always replaces them. That structure (e.g., a hotel, desalination plant, coal-fired power plant, nuclear plant, port facility, marina, cruise ship dock) inevitably brings with it associated issues of altered hydrology, erosion, and pollution. Rivers that once traveled through the mangroves before emptying into the sea are blocked or re-routed, causing changes in filtration, sedimentation, temperature, and salinity. These changes in turn can affect the aquatic species, including commercial or subsistence fish species for coastal communities. The developments are often associated with increased levels of pollution as well, including solid waste, pesticides, thermal, biological (invasive species), brine, and oil. In Panama, for example:

“In recent years the biggest regional threats to mangroves are the ever-increasing development of the tourism industry, pollution from runoff of fertilizers and pesticides, and improper disposal of wastes. Oil pollution is not a widespread problem for the region as a whole, but it is a serious threat in Panama owing to the extremely high maritime traffic in the Panama Canal (Spalding et al. 1997, FAO 2007, p. 34).

In other areas where deepwater ports are built to ship mined ore, natural gas, petroleum, chemicals, coal, and other polluting materials, the chances of an oil spill from boat traffic increased dramatically, as do the chances for a spill of hazardous materials. In short, once a development is built, there is little that can be done to maintain healthy, pollution-free coastal ecosystems. As a result, the benefits of every coastal development project should be carefully weighed against the costs of losing the protective, functioning mangrove systems.

Works Cited: 

Food and Agriculture Organization of the United Nations (FAO). 2007. The world’s mangroves 1980–2005. Chapter 6: North and Central America. 

Spalding, M., F. Blasco, and C. Field. 1997. World Mangrove Atlas. Okinawa, Japan: The International Society for Mangrove Ecosystems: 178 pp.


There are approximately 70 species of mangroves around the world (Polidoro et al. 2010). When activities such as logging, shrimp farming, coastal agriculture, hotel development, and other activities are valued over the ecosystem services the intact mangroves provide, genetic diversity is among the first—but least considered—casualty. The trees and associated species (e.g., birds, snakes, crabs) are visibly lost, but so too are the specific genotypes and phenotypes that have evolved in microhabitats around the world to withstand insects, tidal fluctuations, precipitation patterns and salinity regimes. Mangroves are not species-rich to begin with, especially in comparison with other tropical forests (Alongi 2002). And in the areas where replanting is attempted, it is often done with seeds from elsewhere, and often done with one species, rather than the mix of species that originally existed. As Polidoro et al. (2010) have stated:

“Although regeneration of degraded mangrove areas is thought to be a viable option in some areas (Saenger 2002, Walters et al. 2008), successful regeneration is generally only achieved by the planting of monocultures of fast-growing species, such as Rhizophora or Avicenna species. Many rare and slow growing species are not replaced (Alongi 2002), and many species cannot be easily replanted with success. In sum, mangrove areas may be able to be rehabilitated in some regions, but species and ecosystems cannot be effectively restored” (p. 8).

Thus, once these species and subspecies are lost, they cannot be recovered, no matter how many well-intentioned restoration efforts are made. The solution to ensuring the mangroves are there to provide the ecosystem services we depend on is not to remove them in the first place.

Works Cited: 

Alongi, D. M. 2002. Present state and future of the world’s mangrove forests. Environmental Conservation 29: 331–349.

Polidoro, B. A., K. E. Carpenter, L. Collins, N. C. Duke, A. M. Ellison, J. C. Ellison, E. J. Farnsworth, E. S. Fernando, K. Kathiresan, N. E. Koedam, S. R. Livingstone, T. Miyagi, G. E. Moore, N. N. Vien, J. E. Ong, J. H. Primavera, S. G. Salmo, J. C. Sanciangco, S. Sukardjo, Y. M. Wang, and J. W. H. Yong. 2010. The loss of species: Mangrove extinction risk and geographic areas of global concern. PLoS ONE 5(4): e10095. 10.1371/journal.pone.0010095.

Saenger, P. 2002. Mangrove ecology, silviculture and conservation. Dordrecht: Kluwer Academic Publishers. 372 pp.

Walters, B. B., P Rönnbäck, J. M. Kovacs, B. Crona, S. A. Hussain, R. Badola, J. H. Primavera, E. Barbier, and F. Dahdouh-Guebas 2008. Ethnobiology, socio-economics and management of mangrove forests: a review. Aquatic Botany 89: 220–236.

Aquaculture, Agriculture & Salt Production

The close proximity of mangroves to the ocean makes them ideal locations for shrimp farming and other kinds of mariculture. Further, they are areas rich in nutrients, and part of larger wetland systems, making them attractive as agricultural areas. Finally, these areas near the sea are prized for salt production. As a result, hundreds of thousands of hectares of mangrove forests have been cleared, and the hydrology has been altered, in order to intensify commercial production of shrimp and other species, cultivate agricultural crops, and create salt ponds. The delicate tidal regimes are interrupted and the balance between fresh and salt water is lost. The intensive mariculture operations are most often constructed for export. The shrimp and other species that are raised and harvested from the artificial ponds are fed specific diets that often include chemicals. Extra nutrients from the concentration of food and animals cause eutrophication, which harms the surrounding marine habitats by lowering oxygen levels and changing species distributions. The chemicals enter the food chain and can harm nearby species. Shrimp farm activity alone has been responsible for the loss of 38 percent of the world’s healthy mangroves; the percent climbs to 52 if all agricultural activities are counted (Ellison 2008). Between 1980 and 2005, shrimp and salt production together were responsible for the loss of 85,000 and 80,000 hectares of mangroves in Honduras and Panama, respectively (FAO 2007). If world demand continues for farmed shrimp and other mariculture species, then they must be farmed in land-based facilities, with state-of-the-art water treatment facilities and environmentally responsible management plans. Non-mangrove areas where trees have already been cleared can be used for agriculture and salt ponds.

Works Cited: 

Ellison, A. M. 2008. Managing mangroves with benthic biodiversity in mind: Moving beyond roving banditry. J Sea Res 59: 2–15.

Food and Agriculture Organization of the United Nations (FAO). 2007. The world’s mangroves 1980-2005. Chapter 6. North and Central America. FAO Forestry Paper 153.

Climate Change

Climate change is causing two important impacts along the world’s coastlines. Sea levels are rising and the chemistry of the oceans is shifting (IPCC 2007 and NRC 2011). The rates at which these impacts are occurring is likely to exceed the ability of mangrove forests and the species that live within them to adapt (Gilman et al. 2008).

In areas with upland coastal development, mangroves cannot retreat landward. Mangroves around the world are adapted to specific tidal regimes. If they spend increasing amounts of time inundated, at some point they will not be able to rid themselves of the ocean salt quickly enough, and will whither and die. They will also not receive the nutrients and sediment from freshwater flowing seaward that they require to survive. Compounding this, as the ocean becomes more acidic, mangrove animals with shells and other hard structures (e.g., oysters, snails, crabs, sea stars) will have an increasingly difficult time taking up calcium carbonate from seawater, leaving them with developmental deformities and thin, less protective shells as adults (Doney et al. 2012). And coral reefs—already stressed by increasing temperatures and bleaching—will likewise be weakened by increasing acidity (Hoegh-Guldberg et al. 2007). Many species—including many commercial fishery species—rely on both mangrove and reef habitats during different parts of their life cycle. Climate change directly threatens these habitats, which are responsible for providing food to billions of people around the world. Mangroves provide the critical nursery and adult habitats for 30-80% of commercial fisheries around the world (Rönnbäck 1999). Finally, mangroves are among the most important carbon sinks on the planet (Donato et al. 2011). Losing them will cause even greater carbon releases (Donato et al. 2011), creating a positive feedback loop that will further exacerbate sea level rise and increased ocean acidity.

Works Cited: 

Donato, D. C., J. B. Kauffman, D. Murdiyarso, S. Kurnianto, M. Stidham, and M. Kanninen. 2011. Mangroves among the most carbon-rich forests in the tropics. Nature Geoscience 4: 293-297.

Doney, S. C., M. Ruckelshaus, J. E. Duffy, J. P. Barry, F. Chan, C. A. English, et al. 2012. Climate change impacts on marine ecosystems. Annual Review of Marine Science 4: 11-37.

Gilman, E. L., J. Ellison, N. C. Duke, and C. Field. 2008. Threats to mangroves from climate change and adaptation options. Aquatic Botany 89: 237-250.

Hoegh-Guldberg, O., P. J. Mumby, A. J. Hooten, R. S. Steneck, P. Greenfield, E. Gomez, et al. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318: 1737-1742.

International Panel on Climate Change (IPCC). 2007: Synthesis Report. Pachauri, R. K. & A. Reisinger, eds.) 104.

National Research Council (NRC). 2011. Climate stabilization targets: emissions, concentrations and impacts over decades to Millennia. Washington DC: National Academies Press. 298.

Rönnbäck, P. 1999. The ecological basis for economic value of seafood production supported by mangrove ecosystems. Ecological Economics 29: 235–252.


Most destructive uses of mangrove forests require their removal. The motivations behind deforestation include direct use of the mangrove wood and leaf products, use of the wetland habitat, or complete fill and conversion for coastal developments.

Deforestation for fuel & timber accounts for the ongoing loss of approximately 26 percent of existing mangroves (Valiela et al. 2001). Mangrove reforestation has had very low success, although new hydrology-based methods may be more promising (Lewis & Gilmore 2007). Even so, we cannot rely on reforestation to prevent mangrove loss. These fragile and rare ecosystems are being lost at such a tremendous rate that mangrove experts predict that without changes to current practices, mangroves will be functionally extinct in less than a century (Duke et al. 2007). A world without mangroves means a world without most fisheries, without bioshields from storms, and without many bird and other species. The loss of mangroves as a unique habitat would directly jeopardize more than a billion of the world’s human population.

Works Cited: 

Duke, N. C., J.-O. Meynecke, S. Dittmann, A. M. Ellison, K. Anger, U. Berger, S. Cannicci, K. Diele, K. C. Ewel, C. D. Field, N. Koedam, S. Y. Lee, C. Marchand, I. Nordhaus, and F. Dahdouh-Guebas. 2007. A world without mangroves? Science 317: 41–42.

Lewis III, R. R. and R. G. Gilmore. 2007. Important considerations to achieve successful mangrove forest restoration with optimum fish habitat. 2007. Bulletin of Marine Science 80(3): 823–837.

Valiela I., J. L. Bowen, J. K. York. 2001. Mangrove forests: One of the world’s threatened major tropical environments. BioScience 51: 807–815.

This project has been made possible by the generous support of the Philip Stoddard Brown and Adele Smith Brown Foundation.

Many thanks to the following volunteers, who have contributed their time to make the Mangrove Science Database possible: Bren Catt, Alexander Erwig, Kergis Hiebert, Laura Krogman, Eliza Pearce, Madeleine Rasmussen, and Rachel Tarbet.

Climate Litigation

The damage that humans are doing to the global climate may be one of the gravest injustices of all time.