Mangrove

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For the ship, see USLHT Mangrove. For the restaurant in London, see Mangrove restaurant. For the 2020 Steve McQueen film, see Mangrove (film).
Mangroves are adapted to saline conditions

A mangrove is a shrub or small tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves occur worldwide in the tropics and subtropics and even some temperate coastal areas, mainly between latitudes 30° N and 30° S, with the greatest mangrove area within 5° of the equator.[1][2] Mangrove plant families first appeared during the Late Cretaceous to Paleocene epochs, and became widely distributed in part due to the movement of tectonic plates. The oldest known fossils of mangrove palm date to 75 million years ago.[2]

The word "mangrove" is used in at least three senses:

  • most broadly to refer to the habitat and entire plant assemblage or mangal,[3][4][page needed] for which the terms mangrove forest biome and mangrove swamp are also used;
  • to refer to all trees and large shrubs in a mangrove swamp;[3] and
  • narrowly to refer only to mangrove trees of the genus Rhizophora of the family Rhizophoraceae.[5]

Mangroves are salt-tolerant trees, also called halophytes, and are adapted to live in harsh coastal conditions. They contain a complex salt filtration system and a complex root system to cope with saltwater immersion and wave action. They are adapted to the low-oxygen conditions of waterlogged mud,[6] but are most likely to thrive in the upper half of the intertidal zone.[7]

The mangrove biome, or mangal, is a distinct saline woodland or shrubland habitat characterized by depositional coastal environments, where fine sediments (often with high organic content) collect in areas protected from high-energy wave action. The saline conditions tolerated by various mangrove species range from brackish water, through pure seawater (3 to 4% salinity), to water concentrated by evaporation to over twice the salinity of ocean seawater (up to 9% salinity).[8][9]

Beginning in 2010[10][1] remote sensing technologies and global data have been used to assess areas, conditions and deforestation rates of mangroves around the world.[2] In 2018, the Global Mangrove Watch Initiative released a new global baseline which estimates the total mangrove forest area of the world as of 2010 at 137,600 km2 (53,100 sq mi), spanning 118 countries and territories.[2][10] Mangrove loss continues due to human activity, with a global annual deforestation rate estimated at 0.16%, and per-country rates as high as 0.70%. Degradation in quality of remaining mangroves is also an important concern.[2]

There is interest in mangrove restoration for several reasons. Mangroves support sustainable coastal and marine ecosystems. They protect nearby areas from tsunamis and extreme weather events. Mangrove forests are also effective at carbon sequestration and storage and impede climate change.[2][11][12] The success of mangrove restoration may depend heavily on engagement with local stakeholders, and on careful assessment to ensure that growing conditions will be suitable for the species chosen.[7]

Etymology[edit]

Etymology of the English term mangrove can only be speculative and is disputed.[13]: 1–2  [3] The term may have come to English from the Portuguese mangue or the Spanish mangle.[3] Farther back, it may be traced to South America and Cariban and Arawakan languages[14] such as Taíno.[15] Other possibilities include the Malay language manggi-manggi[3][13] and the Guarani language.[citation needed] The English usage may reflect a corruption via folk etymology of the words mangrow and grove.[14][13][16]

Ecology[edit]

The world's mangrove forests in 2000

Mangrove swamps (mangals) are found in tropical and subtropical tidal areas. Areas where mangroves occur include estuaries and marine shorelines.[17]

The intertidal existence to which these trees are adapted represents the major limitation to the number of species able to thrive in their habitat. High tide brings in salt water, and when the tide recedes, solar evaporation of the seawater in the soil leads to further increases in salinity. The return of tide can flush out these soils, bringing them back to salinity levels comparable to that of seawater.[2][7]

At low tide, organisms are also exposed to increases in temperature and reduced moisture before being then cooled and flooded by the tide. Thus, for a plant to survive in this environment, it must tolerate broad ranges of salinity, temperature, and moisture, as well as several other key environmental factors—thus only a select few species make up the mangrove tree community.[7][2]

About 110 species are considered mangroves, in the sense of being trees that grow in such a saline swamp,[17] though only a few are from the mangrove plant genus, Rhizophora. However, a given mangrove swamp typically features only a small number of tree species. It is not uncommon for a mangrove forest in the Caribbean to feature only three or four tree species. For comparison, the tropical rainforest biome contains thousands of tree species, but this is not to say mangrove forests lack diversity. Though the trees themselves are few in species, the ecosystem that these trees create provides a home (habitat) for a great variety of other species, including as many as 174 species of marine megafauna.[18]

Above- and below-water view of mangrove roots

Mangrove plants require a number of physiological adaptations to overcome the problems of low environmental oxygen levels, high salinity, and frequent tidal flooding. Each species has its own solutions to these problems; this may be the primary reason why, on some shorelines, mangrove tree species show distinct zonation. Small environmental variations within a mangal may lead to greatly differing methods for coping with the environment. Therefore, the mix of species is partly determined by the tolerances of individual species to physical conditions, such as tidal flooding and salinity, but may also be influenced by other factors, such as crabs preying on plant seedlings.[19]

Once established, mangrove roots provide an oyster habitat and slow water flow, thereby enhancing sediment deposition in areas where it is already occurring. The fine, anoxic sediments under mangroves act as sinks for a variety of heavy (trace) metals which colloidal particles in the sediments have concentrated from the water. Mangrove removal disturbs these underlying sediments, often creating problems of trace metal contamination of seawater and organisms of the area.[20]

Mangrove swamps protect coastal areas from erosion, storm surge (especially during tropical cyclones), and tsunamis.[21][22][23] They limit high-energy wave erosion mainly during events such as storm surges and tsunamis.[24] The mangroves' massive root systems are efficient at dissipating wave energy.[25] Likewise, they slow down tidal water enough so that its sediment is deposited as the tide comes in, leaving all except fine particles when the tide ebbs.[26] In this way, mangroves build their environments.[21] Because of the uniqueness of mangrove ecosystems and the protection against erosion they provide, they are often the object of conservation programs,[7] including national biodiversity action plans.[22]

The unique ecosystem found in the intricate mesh of mangrove roots offers a quiet marine habitat for young organisms.[27] In areas where roots are permanently submerged, the organisms they host include algae, barnacles, oysters, sponges, and bryozoans, which all require a hard surface for anchoring while they filter-feed. Shrimps and mud lobsters use the muddy bottoms as their home.[28] Mangrove crabs eat the mangrove leaves, adding nutrients to the mangal mud for other bottom feeders.[29] In at least some cases, the export of carbon fixed in mangroves is important in coastal food webs.[30]

Mangrove plantations in Vietnam, Thailand, Philippines, and India host several commercially important species of fish and crustaceans.[31]

Nipa palms (Nypa fruticans), the only palm species fully adapted to the mangrove biome, growing along the Loboc River, Bohol, Philippines

Mangrove forests can decay into peat deposits because of fungal and bacterial processes as well as by the action of termites. It becomes peat in good geochemical, sedimentary, and tectonic conditions.[32] The nature of these deposits depends on the environment and the types of mangroves involved. In Puerto Rico, the red, white, and black mangroves occupy different ecological niches and have slightly different chemical compositions, so the carbon content varies between the species, as well between the different tissues of the plant (e.g., leaf matter versus roots).[32]

In Puerto Rico, there is a clear succession of these three trees from the lower elevations, which are dominated by red mangroves, to farther inland with a higher concentration of white mangroves.[32] Mangrove forests are an important part of the cycling and storage of carbon in tropical coastal ecosystems.[32] Knowing this, scientists seek to reconstruct the environment and investigate changes to the coastal ecosystem over thousands of years using sediment cores.[33] However, an additional complication is the imported marine organic matter that also gets deposited in the sediment due to the tidal flushing of mangrove forests.[32]

Termites play an important role in the formation of peat from mangrove materials.[32] They process fallen leaf litter, root systems and wood from mangroves into peat to build their nests.[32] Termites stabilise the chemistry of this peat and represent approximately 2% of above ground carbon storage in mangroves.[32] As the nests are buried over time this carbon is stored in the sediment and the carbon cycle continues.[32]

Mangroves are an important source of blue carbon. Globally, mangroves stored 4.19 Gt (9.2×1012 lb) of carbon in 2012.[34] Two percent of global mangrove carbon was lost between 2000 and 2012, equivalent to a maximum potential of 0.316996250 Gt (6.9885710×1011 lb) of CO2 emissions.[34]

Globally, mangroves have been shown to provide measurable economic protections to coastal communities affected by tropical storms.[35]

Biology[edit]

Red mangrove, Rhizophora mangle
Pneumatophorous aerial roots of the grey mangrove (Avicennia marina)
Salt crystals formed on an Avicennia marina leaf
Rhizophora mangle seeds germinate while still on the parent tree.

Of the recognized 110 mangrove species, only about 54 species in 20 genera from 16 families constitute the "true mangroves", species that occur almost exclusively in mangrove habitats.[4] Demonstrating convergent evolution, many of these species found similar solutions to the tropical conditions of variable salinity, tidal range (inundation), anaerobic soils, and intense sunlight. Plant biodiversity is generally low in a given mangrove.[17] The greatest biodiversity of mangroves occurs in Southeast Asia, particularly in the Indonesian archipelago.[36]

Adaptations to low oxygen[edit]

Red mangroves, which can survive in the most inundated areas, prop themselves above the water level with stilt or prop roots and can then absorb air through pores in their bark (lenticels).[37]Black mangroves live on higher ground and make many pneumatophores (specialized root-like structures which stick up out of the soil like straws for breathing).[38][39]

These "breathing tubes" typically reach heights of up to 30 cm (12 in), and in some species, over 3 m (9.8 ft). The four types of pneumatophores are stilt or prop type, snorkel or peg type, knee type, and ribbon or plank type. Knee and ribbon types may be combined with buttress roots at the base of the tree. The roots also contain wide aerenchyma to facilitate transport within the plants.[citation needed]

Nutrient uptake[edit]

Because the soil is perpetually waterlogged, little free oxygen is available. Anaerobic bacteria liberate nitrogen gas, soluble ferrum (iron), inorganic phosphates, sulfides, and methane, which make the soil much less nutritious.[citation needed] Pneumatophores (aerial roots) allow mangroves to absorb gases directly from the atmosphere, and other nutrients such as iron, from the inhospitable soil. Mangroves store gases directly inside the roots, processing them even when the roots are submerged during high tide.

Limiting salt intake[edit]

Red mangroves exclude salt by having significantly impermeable roots which are highly suberised (impregnated with suberin), acting as an ultra-filtration mechanism to exclude sodium salts from the rest of the plant. Analysis of water inside mangroves has shown 90% to 97% of salt has been excluded at the roots. In a frequently cited concept that has become known as the "sacrificial leaf", salt which does accumulate in the shoot (sprout) than concentrates in old leaves, which the plant then sheds. However, recent research suggests the older, yellowing leaves have no more measurable salt content than the other, greener leaves.[40] Red mangroves can also store salt in cell vacuoles. White and grey mangroves can secrete salts directly; they have two salt glands at each leaf base (correlating with their name—they are covered in white salt crystals).

Limiting water loss[edit]

Because of the limited fresh water available in salty intertidal soils, mangroves limit the amount of water they lose through their leaves. They can restrict the opening of their stomata (pores on the leaf surfaces, which exchange carbon dioxide gas and water vapor during photosynthesis). They also vary the orientation of their leaves to avoid the harsh midday sun and so reduce evaporation from the leaves. Anthony Calfo, a noted aquarium author, observed anecdotally that a red mangrove in captivity grows only if its leaves are misted with fresh water several times a week, simulating frequent tropical rainstorms.[41]

Increasing survival of offspring[edit]

A germinating Avicennia seed.

In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. Mangrove seeds are buoyant and are therefore suited to water dispersal. Unlike most plants, whose seeds germinate in soil, many mangroves (e.g. red mangrove) are viviparous, meaning their seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit (e.g. Aegialitis, Avicennia and Aegiceras), or out through the fruit (e.g. Rhizophora, Ceriops, Bruguiera and Nypa) to form a propagule (a ready-to-go seedling) which can produce its own food via photosynthesis.

The mature propagule then drops into the water, which can transport it great distances. Propagules can survive desiccation and remain dormant for over a year before arriving in a suitable environment. Once a propagule is ready to root, its density changes so that the elongated shape now floats vertically rather than horizontally. In this position, it is more likely to lodge in the mud and root. If it does not root, it can alter its density and drift again in search of more favorable conditions.

Taxonomy and evolution[edit]

The following listings, based on Tomlinson, 2016, give the mangrove species in each listed plant genus and family.[42] Mangrove environments in the Eastern Hemisphere harbor six times as many species of trees and shrubs as do mangroves in the New World. Genetic divergence of mangrove lineages from terrestrial relatives, in combination with fossil evidence, suggests mangrove diversity is limited by evolutionary transition into the stressful marine environment, and the number of mangrove lineages has increased steadily over the Tertiary with little global extinction.[43]

True mangroves[edit]

True mangroves (major components or strict mangroves)
Following Tomlinson, 2016, the following 35 species are the true mangroves, contained in 5 families and 9 genera [42]: 29–30 
Included on green backgrounds are annotations about the genera made by Tomlinson
Family Genus Mangrove species Common name
Arecaceae Monotypic subfamily within the family
Nypa Nypa fruticans Mangrove palm Nypa fruticans - Taki - North 24 Parganas 2015-01-13 4729.JPG
Avicenniaceae
(disputed) 		Old monogeneric family, now subsumed in Acanthaceae, but clearly isolated
Avicennia Avicennia alba Avicennia alba.jpg
Avicennia balanophora
Avicennia bicolor
Avicennia integra
Avicennia marina grey mangrove
(subspecies: australasica,
eucalyptifolia, rumphiana) 		Mangroves at Muzhappilangad101 (11).jpg
Avicennia officinalis Indian mangrove Avicennia officinalis (2682502984).jpg
Avicennia germinans black mangrove Avicennia germinans-flowers2.jpg
Avicennia schaueriana Avicennia cf. schaueriana mangue-preto.jpg
Avicennia tonduzii
Combretaceae Tribe Lagunculariae (including Macropteranthes = non-mangrove)
Laguncularia Laguncularia racemosa white mangrove Laguncularia racemosa flowers.jpg
Lumnitzera Lumnitzera racemosa white-flowered black mangrove Lumnitzera racemosa (11544407974).jpg
Lumnitzera littorea Lumnitzera littorea.jpg
Rhizophoraceae Rhizophoraceae collectively form the tribe Rhizophorae, a monotypic group, within the otherwise terrestrial family
Bruguiera Bruguiera cylindrica Mangroves at Muzhappilangad004.jpg
Bruguiera exaristata rib-fruited mangrove Flowers of Bruguiera exaristata.png
Bruguiera gymnorhiza oriental mangrove Bruguiera gymnorrhiza.jpg
Bruguiera hainesii Bruguiera hainesii.jpg
Bruguiera parviflora Brugu parvi 111021-18862 Fl kbu.jpg
Bruguiera sexangula upriver orange mangrove Bruguiera sexangula.jpg
Ceriops Ceriops australis yellow mangrove Yellow mangrove.jpg
Ceriops tagal spurred mangrove Rhizophoreae sp Blanco2.415-cropped.jpg
Kandelia Kandelia candel Kandelia candel 9429.jpg
Kandelia obovata 秋茄樹(水筆仔) Kandelia obovata -香港大埔滘白鷺湖 Lake Egret Park, Hong Kong- (9240150714).jpg
Rhizophora Rhizophora apiculata
Rhizophora harrisonii
Rhizophora mangle red mangrove
Rhizophora mucronata Asiatic mangrove Rhizophora mucronata Propagules.jpg
Rhizophora racemosa
Rhizophora samoensis Samoan mangrove
Rhizophora stylosa spotted mangrove,
Rhizophora x lamarckii
Lythraceae Sonneratia Sonneratia alba Sonneratia alba - fruit (8349980264).jpg
Sonneratia apetala
Sonneratia caseolaris
Sonneratia ovata
Sonneratia griffithii

Minor components[edit]

Minor components
Tomlinson, 2016, lists about 19 species as minor mangrove components, contained in 10 families and 11 genera [42]: 29–30 
Included on green backgrounds are annotations about the genera made by Tomlinson
Family Genus Species Common name
Euphorbiaceae This genus includes about 35 non-mangrove taxa
Excoecaria Excoecaria agallocha milky mangrove, blind-your-eye mangrove and river poison tree Excoecaria agallocha (Blind Your Eye) W IMG 6929.jpg
Lythraceae Genus distinct in the family
Pemphis Pemphis acidula bantigue or mentigi Pemphis acidula.jpg
Malvaceae Formerly in Bombacaceae, now an isolated genus in subfamily Bombacoideeae
Camptostemon Camptostemon schultzii kapok mangrove Camptostemon schultzii.png
Camptostemon philippinense Camptostemon philippinense.jpg
Meliaceae Genus of 3 species, one non-mangrove, forms tribe Xylocarpaeae with Carapa, a non–mangrove
Xylocarpus Xylocarpus granatum Xylocarpus granatum.jpg
Xylocarpus moluccensis Xyloc moluc 191103-2935 skd.jpg
Myrtaceae An isolated genus in the family
Osbornia Osbornia octodonta mangrove myrtle Osbor octod 110319-13636 sagt.jpg
Pellicieraceae Monotypic genus and family of uncertain phylogenetic position
Pelliciera Pelliciera rhizophorae, tea mangrove Pelliciera rhizophorae.jpg
Plumbaginaceae Isolated genus, at times segregated as family Aegialitidaceae
Aegialitis Aegialitis annulata club mangrove Aegialitis annulata 30694138.jpg
Aegialitis rotundifolia Aegialitis rotundifolia 2.jpg
Primulaceae Formerly an isolated genus in Myrsinaceae
Aegiceras Aegiceras corniculatum black mangrove, river mangrove or khalsi Aegiceras corniculatum at Muzhappilangad, Kannur 3.jpg
Aegiceras floridum
Pteridaceae A fern somewhat isolated in its family
Acrostichum Acrostichum aureum golden leather fern, swamp fern or mangrove fern Acrostichum-aureum.jpg
Acrostichum speciosum mangrove fern Acrostichum speciosum RBG Sydney.jpg
Rubiaceae A genus isolated in the family
Scyphiphora Scyphiphora hydrophylacea nilad Scyphip hydrop 111021-19089 kbu.jpg

Distribution[edit]

Main article: Mangrove tree distribution
Further information: List of mangrove ecoregions

Mangroves can be found in over one hundred countries and territories in the tropical and subtropical regions of the world. The largest percentage of mangroves is found between the 5° N and 5° S latitudes. Approximately 75% of world's mangroves are found in just 15 countries.[1] Estimates of mangrove area based on remote sensing and global data tend to be lower than estimates based on literature and surveys for comparable periods.[2]

In 2018, the Global Mangrove Watch Initiative released a global baseline based on remote sensing and global data for 2010. They estimated the total mangrove forest area of the world as of 2010 at 137,600 km2 (53,100 sq mi), spanning 118 countries and territories.[2][10] Following the conventions for identifying geographic regions from the Ramsar Convention on Wetlands, researchers also reported that Asia has the largest share (38.7%) of the world's mangroves, followed by Latin America and the Caribbean (20.3%) Africa (20.0%), Oceania (11.9%), and Northern America (8.4%).[10]

Exploitation and conservation[edit]

Mangrove roots act as a net, retaining waste. Mayotte at low tide
Mangroves in West Bali National Park, Indonesia

Adequate data is only available for about half of the global area of mangroves. However, of those areas for which data has been collected, it appears that 35% of the mangroves have been destroyed.[44] Since the 1980s, around 2% of mangrove area is estimates to be lost each year.[45] Assessments of global variation in mangrove loss indicates that national regulatory quality mediates how different drivers and pressures influence loss rates.[46]

The United Nations Environment Programme and Hamilton (2013), estimate that shrimp farming causes approximately a quarter of the destruction of mangrove forests.[47][48] Likewise, the 2010 update of the World Mangrove Atlas indicated that approximately one fifth of the world's mangrove ecosystems have been lost since 1980,[49] although this rapid loss rate appears to have decreased since 2000 with global losses estimated at between 0.16% and 0.39% annually between 2000 and 2012.[50] Despite global loss rates decreasing since 2000, Southeast Asia remains an area of concern with loss rates between 3.58% and 8.08% between 2000 and 2012.[50]

By far the most damaging form of shrimp farming is when a closed ponds system (non-integrated multi-trophic aquaculture) is used (as these require destruction of a large part of the mangrove, and use antibiotics and disinfectants to suppress diseases that occur in this system, and which may also leak into the surrounding environment). Far less damage occurs when integrated mangrove-shrimp aquaculture is used (as this is connected to the sea and subjected to the tides, and less diseases occur, and as far less mangrove is destroyed for it).[51]

Grassroots efforts to protect mangroves from development and from citizens cutting down the mangroves for charcoal production,[52][53] cooking, heating and as a building material are becoming more popular. Solar cookers are distributed by many ngos as a low-cost alternative to wood and charcoal stoves. These may help in reducing the demand for charcoal.

  • In Thailand, community management has been effective in restoring damaged mangroves.[54] Also, production of mangrove honey is practiced, as a way to generate sustainable income for nearby people, keeping them from destroying the mangrove and generate but a short-term revenue.[55][56]
  • In Madagascar, honey too is produced in mangroves as a source of (non-destructive) income generation. In addition, silk pods from endemic silkworm species are also collected in the Madagascar mangroves for wild silk production.[57][53]
  • In the Bahamas, for example, active efforts to save mangroves are occurring on the islands of Bimini and Great Guana Cay.
  • In Trinidad and Tobago as well, efforts are underway to protect a mangrove threatened by the construction of a steel mill and a port.[citation needed]
  • Within northern Ecuador mangrove regrowth is reported in almost all estuaries and stems primarily from local actors responding to earlier periods of deforestation in the Esmeraldas region.[58]

Mangroves have been reported to be able to help buffer against tsunami, cyclones, and other storms, and as such may be considered a flagship system for ecosystem-based adaptation to the impacts of climate change. One village in Tamil Nadu was protected from tsunami destruction—the villagers in Naluvedapathy planted 80,244 saplings to get into the Guinness Book of World Records. This created a kilometre-wide belt of trees of various varieties. When the 2004 tsunami struck, much of the land around the village was flooded, but the village itself suffered minimal damage.[59]

Shrimp ponds in mangrove forests like these leave massive amounts of water pollution and compounds the negative effects of deoxygenation in mangrove forests.

Ocean deoxygenation[edit]

Compared to seagrass meadows and coral reefs, hypoxia is more common on a regular basis in mangrove ecosystems, through ocean deoxygenation is compounding the negative effects by anthropogenic nutrient inputs and land use modification.[60]

Like seagrass, mangrove trees transport oxygen to roots of rhizomes, reduce sulfide concentrations, and alter microbial communities. Dissolved oxygen is more readily consumed in the interior of the mangrove forest. Anthropogenic inputs may push the limits of survival in many mangrove microhabitats. For example, shrimp ponds constructed in mangrove forests are considered the greatest anthropogenic threat to mangrove ecosystems. These shrimp ponds reduce estuary circulation and water quality which leads to the promotion of diel-cycling hypoxia. When the quality of the water degrades, the shrimp ponds are quickly abandoned leaving massive amounts of wastewater. This is a major source of water pollution that promotes ocean deoxygenation in the adjacent habitats.[60][61]

Due to these frequent hypoxic conditions, the water does not provide habitats to fish. When exposed to extreme hypoxia, ecosystem function can completely collapse. Extreme deoxygenation will affect the local fish populations, which are an essential food source. The environmental costs of shrimp farms in the mangrove forests grossly outweigh the economic benefits of them. Cessation of shrimp production and restoration of these areas reduce eutrophication and anthropogenic hypoxia.[60]

Reforestation[edit]

Mangroves in Bohol, Philippines
Main article: Mangrove restoration

In some areas, mangrove reforestation and mangrove restoration is also underway. Red mangroves are the most common choice for cultivation, used particularly in marine aquariums in a sump to reduce nitrates and other nutrients in the water. Mangroves also appear in home aquariums, and as ornamental plants, such as in Japan.[citation needed]

In Senegal, Haïdar El Ali has started the fr project, which (amongst others) focuses on reforesting several areas with mangroves.[62]

The Manzanar Mangrove Initiative is an ongoing experiment in Arkiko, Eritrea, part of the Manzanar Project founded by Gordon H. Sato, establishing new mangrove plantations on the coastal mudflats. Initial plantings failed, but observation of the areas where mangroves did survive by themselves led to the conclusion that nutrients in water flow from inland were important to the health of the mangroves. Trials with the Eritrean Ministry of Fisheries followed, and a planting system was designed to provide the nitrogen, phosphorus, and iron missing from seawater.[63][64]

The propagules are planted inside a reused galvanized steel can with the bottom knocked out; a small piece of iron and a pierced plastic bag with fertilizer containing nitrogen and phosphorus are buried with the propagule. As of 2007, after six years of planting, 700,000 mangroves are growing; providing stock feed for sheep and habitat for oysters, crabs, other bivalves, and fish.[63][64]

Another method of restoring mangroves is by using quadcopters (which are able to carry and deposit seed pods). According to Irina Fedorenko, an amount of work equivalent to weeks of planting using traditional methods can be done by a drone in days, and at a fraction of the cost.[65]

Seventy percent of mangrove forests have been lost in Java, Indonesia. Mangroves formerly protected the island's coastal land from flooding and erosion.[66] Wetlands International, an NGC based in the Netherlands, in collaboration with nine villages in Demak where lands and homes had been flooded, began reviving mangrove forests in Java. Wetlands International introduced the idea of developing tropical versions of techniques traditionally used by the Dutch to catch sediment in North Sea coastal salt marshes.[66] Originally, the villagers constructed a sea barrier by hammering two rows of vertical bamboo poles into the seabed and filling the gaps with brushwood held in place with netting. Later the bamboo was replaced by PVC pipes filled with concrete. As sediment gets deposited around the brushwood, it serves to catch floating mangrove seeds and provide them with a stable base to germinate, take root and regrow. This creates a green belt of protection around the islands. As the mangroves mature, more sediment is held in the catchment area; the process is repeated until a mangrove forest has been restored. Eventually the protective structures will not be needed.[66] By late 2018, 16 km (9.9 mi) of brushwood barriers along the coastline had been completed.[66]

A concern over reforestation is that although it supports increases in mangrove area it may actually result in a decrease in global mangrove functionality and poor restoration processes may result in longer term depletion of the mangrove resource.[67]

National studies[edit]

In terms of local and national studies of mangrove loss, the case of Belize's mangroves is illustrative in its contrast to the global picture. A recent, satellite-based study[68]—funded by the World Wildlife Fund and conducted by the Water Center for the Humid Tropics of Latin America and the Caribbean (CATHALAC)—indicates Belize's mangrove cover declined by a mere 2% over a 30-year period. The study was born out of the need to verify the popular conception that mangrove clearing in Belize was rampant.[69]

Instead, the assessment showed, between 1980 and 2010, under 16 km2 (6.2 sq mi) of mangroves had been cleared, although clearing of mangroves near Belize's main coastal settlements (e.g. Belize City and San Pedro) was relatively high. The rate of loss of Belize's mangroves—at 0.07% per year between 1980 and 2010—was much lower than Belize's overall rate of forest clearing (0.6% per year in the same period).[70] These findings can also be interpreted to indicate Belize's mangrove regulations (under the nation's)[71] have largely been effective. Nevertheless, the need to protect Belize's mangroves is imperative, as a 2009 study by the World Resources Institute (WRI) indicates the ecosystems contribute US$174 to US$249 million per year to Belize's national economy.[72]

International research[edit]

In May 2019, ORNL DAAC News announced that NASA's Carbon Monitoring System (CMS), using new satellite-based maps of global mangrove forests across 116 countries, had created a new dataset to characterize the "distribution, biomass, and canopy height of mangrove-forested wetlands".[73][11] Mangrove forests move carbon dioxide "from the atmosphere into long-term storage" in greater quantities than other forests, making them "among the planet's best carbon scrubbers" according to a NASA-led study.[11][12]

See also[edit]

References[edit]

  1. ^ a b c Giri, C.; Ochieng, E.; Tieszen, L. L.; Zhu, Z.; Singh, A.; Loveland, T.; Masek, J.; Duke, N. (January 2011). "Status and distribution of mangrove forests of the world using earth observation satellite data: Status and distributions of global mangroves". Global Ecology and Biogeography. 20 (1): 154–159. doi:10.1111/j.1466-8238.2010.00584.x. Retrieved 12 August 2021.
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Further reading[edit]

External links[edit]

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