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A mangrove is a
shrub
A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
or tree that grows in coastal
saline or
brackish water
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...
. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in several plant families. They occur worldwide in the
tropics
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
and
subtropics
The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 35° north and ...
and even some
temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
coastal areas, mainly between latitudes 30° N and 30° S, with the greatest mangrove area within 5° of the
equator
The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
.
Mangrove plant families first appeared during the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
to
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
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.
Mangroves are salt-tolerant trees, also called
halophyte
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. T ...
s, 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, but are most likely to thrive in the upper half of the
intertidal zone
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
.
The mangrove
biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
, often called the
mangrove forest
Mangrove forests, also called mangrove swamps, mangrove thickets or mangals, are productive wetlands that occur in coastal intertidal zones. Mangrove forests grow mainly at tropical and subtropical latitudes because mangroves cannot withstand fr ...
or mangal, is a distinct saline
woodland
A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see ...
or
shrubland
Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity. It m ...
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).
Beginning in 2010
remote sensing technologies and global data have been used to assess areas, conditions and
deforestation
Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated d ...
rates of mangroves around the world.
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 , spanning 118 countries and territories.
A 2022 study on losses and gains of tidal wetlands estimates a 3,700 km
2 net decrease in global mangrove extent from 1999–2019, which was only partially offset by gains of 1,800 km
2. 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.
There is interest in
mangrove restoration
Mangrove restoration is the regeneration of mangrove forest ecosystems in areas where they have previously existed. The practice of mangrove restoration is grounded in the discipline of restoration ecology, which aims to “ ssistthe recovery of ...
for several reasons. Mangroves support sustainable coastal and marine ecosystems. They protect nearby areas from
tsunamis
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater expl ...
and extreme weather events. Mangrove forests are also effective at
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...
and storage and
mitigate climate change.
As the
effects of climate change
The effects of climate change impact the physical environment, ecosystems and human societies. The environmental effects of climate change are broad and far-reaching. They affect the water cycle, oceans, sea and land ice (glaciers), sea level ...
become more severe, mangrove ecosystems are expected to help local ecosystems adapt and be more resilient to changes like
extreme weather
Extreme weather or extreme climate events includes unexpected, unusual, severe, or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a locat ...
and
sea level rise
Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
. 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.
Etymology
Etymology of the English term ''
mangrove
A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...
'' can only be speculative and is disputed.
The term may have come to English from the Portuguese ' or the Spanish
'.
Further back, it may be traced to South America and
Cariban and
Arawakan languages
Arawakan (''Arahuacan, Maipuran Arawakan, "mainstream" Arawakan, Arawakan proper''), also known as Maipurean (also ''Maipuran, Maipureano, Maipúre''), is a language family that developed among ancient indigenous peoples in South America. Branc ...
such as
Taíno
The Taíno were a historic Indigenous peoples of the Caribbean, indigenous people of the Caribbean whose culture has been continued today by Taíno descendant communities and Taíno revivalist communities. At the time of European contact in the ...
.
Other possibilities include the
Malay language
Malay (; ms, Bahasa Melayu, links=no, Jawi alphabet, Jawi: , Rejang script, Rencong: ) is an Austronesian languages, Austronesian language that is an official language of Brunei, Indonesia, Malaysia, and Singapore, and that is also spo ...
and the
Guarani language
Guaraní (), specifically the primary variety known as Paraguayan Guarani ( "the people's language"), is a South American language that belongs to the Tupi–Guarani family of the Tupian languages. It is one of the official languages of P ...
.
The English usage may reflect a corruption via
folk etymology
Folk etymology (also known as popular etymology, analogical reformation, reanalysis, morphological reanalysis or etymological reinterpretation) is a change in a word or phrase resulting from the replacement of an unfamiliar form by a more famili ...
of the words ''mangrow'' and ''
grove''.
The word "mangrove" is used in at least three senses:
* most broadly to refer to the habitat and entire plant assemblage or ''mangal'',
[Hogarth, Peter J. (1999) ''The Biology of Mangroves'' Oxford University Press, Oxford, England, .] for which the terms ''mangrove forest
biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
'' and ''mangrove swamp'' are also used;
* to refer to all trees and large shrubs in a mangrove
swamp
A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
;
and
* narrowly to refer only to mangrove trees of the genus ''
Rhizophora
''Rhizophora'' is a genus of tropical mangrove trees, sometimes collectively called true mangroves. The most notable species is the red mangrove (''Rhizophora mangle'') but some other species and a few natural hybrids are known. ''Rhizophora'' ...
'' of the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Rhizophoraceae
The Rhizophoraceae is a family of tropical or subtropical flowering plants. It includes around 147 species distributed in 15 genera.Setoguchi, H., Kosuge, K., & Tobe, H. (1999). Molecular Phylogeny of Rhizophoraceae Based on rbcL Gene Sequences. ...
.
File:Mangrove roots at low tide.jpg, Mangrove roots at low tide in the Philippines
File:Mangroves in Kannur, India.jpg, Mangroves are adapted to saline conditions
Biology
Of the recognized 110 mangrove species, only about 54 species in 20 genera from 16
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
constitute the "true mangroves", species that occur almost exclusively in mangrove habitats.
Demonstrating
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
, many of these species found similar solutions to the tropical conditions of variable salinity, tidal range (inundation),
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
soils, and intense sunlight. Plant biodiversity is generally low in a given mangrove.
The greatest biodiversity of mangroves occurs in
Southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
, particularly in the
Indonesian archipelago
The islands of Indonesia, also known as the Indonesian Archipelago ( id, Kepulauan Indonesia) or Nusantara, may refer either to the islands comprising the country of Indonesia or to the geographical groups which include its islands.
History ...
.
Adaptations to low oxygen
The red mangrove (''
Rhizophora mangle
''Rhizophora mangle'', the red mangrove, is distributed in Estuary, estuarine ecosystems throughout the tropics. Its Vivipary, viviparous "seeds", in actuality called propagules, become fully mature plants before dropping off the parent tree. Th ...
'') survives in the most inundated areas, props itself above the water level with stilt or prop roots and then absorbs air through
lenticels in its bark.
The black mangrove (''
Avicennia germinans
''Avicennia germinans'', the black mangrove, is a shrub or small tree growing up to 12 meters (39 feet) in the acanthus family, Acanthaceae. It grows in tropical and subtropical regions of the Americas, on both the Atlantic and Pacific Coasts, ...
'') lives on higher ground and develops many specialized root-like structures called
pneumatophore
Aerial roots are roots above the ground. They are almost always adventitious. They are found in diverse plant species, including epiphytes such as orchids (''Orchidaceae''), tropical coastal swamp trees such as mangroves, banyan figs (''Fic ...
s, which stick up out of the soil like straws for breathing.
These "breathing tubes" typically reach heights of up to , and in some species, over . 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
Aerenchyma or aeriferous parenchyma or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and t ...
to facilitate transport within the plants.
Nutrient uptake
Because the soil is perpetually waterlogged, little free oxygen is available.
Anaerobic bacteria
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenat ...
liberate
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
gas, soluble ferrum (iron), inorganic
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
s,
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
s, and
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
, which make the soil much less nutritious. Pneumatophores (
aerial root
Aerial roots are roots above the ground. They are almost always adventitious. They are found in diverse plant species, including epiphytes such as orchids (''Orchidaceae''), tropical coastal swamp trees such as mangroves, banyan figs ('' F ...
s) 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
Red mangroves exclude salt by having significantly impermeable roots which are highly suberised (impregnated with
suberin
Suberin, cutin and lignins are complex, higher plant epidermis and periderm cell-wall macromolecules, forming a protective barrier. Suberin, a complex polyester biopolymer, is lipophilic, and composed of long chain fatty acids called suberin aci ...
), acting as an ultra-filtration mechanism to exclude
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
salts
In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...
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) then 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. Red mangroves can also store salt in cell
vacuole
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
s. 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).
File:Pneumatophore overkill - grey mangrove.JPG, Pneumatophorous aerial roots of the grey mangrove (''Avicennia marina
''Avicennia marina'', commonly known as grey mangrove or white mangrove, is a species of mangrove tree classified in the plant family Acanthaceae (formerly in the Verbenaceae or Avicenniaceae). As with other mangroves, it occurs in the intertid ...
'')
File:Plody mangrovnika (Rhizophora mangle).jpg, Vivipary
In plants, vivipary occurs when seeds or embryos begin to develop before they detach from the parent. Plants such as some Iridaceae and Agavoideae grow cormlets in the axils of their inflorescences. These fall and in favourable circumstances the ...
in ''Rhizophora mangle'' seeds
Limiting water loss
File:Water filtration in mangrove roots.webp,
(a) Schematic of the root. The outermost layer is composed of three layers. The root is immersed in NaCl solution.
(b) Water passes through the outermost layer when a negative suction pressure is applied across the outermost layer. The Donnan potential
Donnan potential is the difference in the Galvani potentials which appears as a result of Donnan equilibrium, named after Frederick G. Donnan, which refers to the distribution of ion species between two ionic solutions separated by a semipermea ...
effect repels Cl− ions from the first sublayer of the outermost layer. Na+ ions attach to the first layer to satisfy the electro-neutrality requirement and salt retention eventually occurs.[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
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
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
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. A captive red mangrove grows only if its leaves are misted with fresh water several times a week, simulating frequent tropical rainstorms.
Filtration of seawater
A 2016 study by Kim ''et al.'' investigated the biophysical characteristics of sea water filtration in the roots of the mangrove ''
Rhizophora stylosa
''Rhizophora stylosa'', the spotted mangrove, red mangrove, small stilted mangrove or stilt-root mangrove, is a tree in the family Rhizophoraceae. The specific epithet ' is from the Latin meaning "stylus form", referring to the flower.
Descript ...
'' from a plant hydrodynamic point of view. ''R. stylosa'' can grow even in saline water and the salt level in its roots is regulated within a certain threshold value through filtration. The root possesses a hierarchical, triple layered pore structure in the
epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
and most Na
+ ions are filtered at the first sublayer of the outermost layer. The high blockage of Na
+ ions is attributed to the high surface
zeta potential
Zeta potential is the electrical potential at the slipping plane. This plane is the interface which separates mobile fluid from fluid that remains attached to the surface.
Zeta potential is a scientific term for electrokinetic potential in coll ...
of the first layer. The second layer, which is composed of
macroporous structures, also facilitates Na
+ ion filtration. The study provides insights into the mechanism underlying water filtration through
halophyte
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. T ...
roots and could serve as a basis for the development of a
bio-inspired method of
desalination
Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in Soil salinity control, soil desalination, which is an issue f ...
.
Uptake of Na
+ ions is desirable for halophytes to build up
osmotic potential
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure s ...
, absorb water and sustain
turgor pressure
Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.
It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...
. However, excess Na
+ions may work on toxic element. Therefore, halophytes try to adjust salinity delicately between growth and survival strategies. In this point of view, a novel sustainable desalination method can be derived from halophytes, which are in contact with saline water through their roots. Halophytes exclude salt through their roots, secrete the accumulated salt through their aerial parts and sequester salt in
senescent
Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...
leaves and/or the bark.
[Tomlinson, P. The botany of mangroves. 16–130(Cambridge University Press, Cambridge, 1986).] Mangroves are facultative halophytes and ''
Bruguiera
''Bruguiera'' is a plant genus in the family Rhizophoraceae. It is a small genus of five mangrove species and three hybrids of the Indian and west Pacific Ocean region, its range extending from East Africa and Madagascar through coastal India ...
'' is known for its special ultrafiltration system that can filter approximately 90% of Na
+ions from the surrounding seawater through the roots. The species also exhibits a high rate of salt rejection. The water-filtering process in mangrove roots has received considerable attention for several decades. Morphological structures of plants and their functions have been evolved through a long history to survive against harsh environmental conditions.
Increasing survival of offspring
In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. Mangrove
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s are buoyant and are therefore suited to water dispersal. Unlike most plants, whose seeds germinate in soil, many mangroves (e.g.
red mangrove Red mangrove may refer to at least three plant species:
* ''Rhizophora mangle''
* ''Rhizophora mucronata''
* ''Rhizophora stylosa''
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