Everything about Mangrove totally explained
Mangroves (generally) are
trees and
shrubs that grow in
saline coastal habitats in the
tropics and
subtropics. The word is used in at least three senses: (1) most broadly to refer to the habitat and entire plant assemblage or
mangal, for which the terms
mangrove swamp and
mangrove forest are also used, (2) to refer to all trees and large shrubs in the mangal, and (3) narrowly to refer to the mangrove
family of plants, the
Rhizophoraceae, or even more specifically just to mangrove trees of the genus
Rhizophora. Mangals are found in
depositional coastal environments where fine sediments, often with high organic content, collect in areas protected from high energy wave action.
Ecology
A mangrove is a plant and mangal is a plant community and habitat where mangroves thrive Each species has its own capabilities and 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 of coping with the environment. Therefore, the mix of species at any location within the intertidal zone is partly determined by the tolerances of individual species to physical conditions, like tidal inundation and salinity, but may also be influenced by other factors such as predation of plant seedlings by crabs.
Once established, roots of mangrove plants provide a habitat for oysters and help to impede water flow, thereby enhancing the deposition of sediment in areas where it's already occurring. Usually, the fine, anoxic sediments under mangroves act as sinks for a variety of
heavy (trace) metals which are scavenged from the overlying seawater by
colloidal particles in the sediments. In areas of the world where mangroves have been removed for development purposes, the disturbance of these underlying sediments often creates problems of trace metal contamination of seawater and
biota.
Mangroves protect the coast from erosion, surge storms (especially during
hurricanes), and tsunamis. Their massive root system is efficient at dissipating wave energy. Likewise, they slow down tidal water enough that its sediment is deposited as the tide comes in and isn't re-suspended when the tide leaves, except for fine particles. As a result, mangroves build their own environment. so their effect on erosion can only be measured in the long-term. Erosion often still occurs on the outer sides of bends in river channels that wind through mangroves, just as new stands of mangroves are appearing on the inner sides where sediment is
accreting.
Mangroves support unique ecosystems, especially on their intricate root systems. The mesh of mangrove
roots produces a quiet marine region for many young organisms. In areas where roots are permanently submerged, they may host a wide variety of organisms, including
algae,
barnacles,
oysters,
sponges, and
bryozoans, which all require a hard substratum for anchoring while they filter feed.
Shrimps and
mud lobsters use the muddy bottom as their home.
Mangrove crabs improve the nutritional quality of the mangal muds for other bottom feeders by mulching the mangrove leaves. In at least some cases, export of carbon fixed in mangroves is important in coastal food webs. The habitats also host several commercially important species of fish and crustaceans. In
Vietnam,
Thailand, the
Philippines, and
India, mangrove plantations are grown in coastal regions for the benefits they provide to coastal fisheries and other uses. Despite replanting programs, over half of the world's mangroves have been lost in recent times.
Biology
A wide variety of plant species can be found in mangrove habitat, but of the recognized 110 species, only about 54 species in 20 genera from 16
families constitute the "true mangroves", species that occur almost exclusively in mangrove habitats and rarely elsewhere
Adaptations to low oxygen
Red mangroves, which can live in the most inundated areas, prop themselves up above the water level with stilt roots and can then take in air through pores in their bark (
lenticels). Black mangroves live on higher ground and make many
pneumatophores (specialised root-like structures which stick up out of the soil like straws for breathing) which are covered in lenticels. These "breathing tubes" typically reach heights of up to thirty centimeters, and in some species, over three meters. There are four types of pneumatophore—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 oxygen transport within the plant.
Limiting salt intake
Red mangroves exclude salt by having rather impermeable roots which are highly
suberised, acting as an ultra-filtration mechanism to exclude
sodium salts from the rest of the plant. Water inside the plant shows that 90%, and in some cases of high salinity, up to 97%, of the salt has been excluded at the roots. Any salt which does accumulate in the shoot is concentrated in old leaves which are then shed, as well as stored away safely in cell
vacuoles. White (or grey) mangroves can secrete salts directly; they've two salt glands at each leaf base (hence their name—they are covered in white salt crystals).
Limiting water loss
Because of the limited availability of freshwater in the salty soils of the intertidal zone, mangrove plants have developed ways of limiting the amount of water that 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 vapour 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, has observed anecdotally that a red mangrove in captivity only grows if its leaves are misted with fresh water several times a week, simulating the frequent rainstorms in the tropics.
Nutrient uptake
The biggest problem that mangroves face is nutrient uptake. Because the soil is perpetually waterlogged, there's little free oxygen. Thus anaerobic
bacteria liberate
nitrogen gas, soluble
iron, inorganic
phosphates,
sulfides, and
methane, which makes the soil much less nutritious and contributes to a mangrove's pungent
odor. Prop root systems allow mangroves to take up gasses directly from the atmosphere, and various other nutrients, like iron, from the inhospitable soil. Gases are quite often stored directly inside the roots and processed even when the roots are submerged during high tide.
Increasing survival of offspring
In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. All mangroves have buoyant
seeds suited to dispersal in water. Unlike most plants, whose seeds germinate in soil, many mangrove plants (for example Red Mangrove) are viviparous, for example, their seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit (for example
Aegialitis,
Acanthus,
Avicennia and
Aegiceras), or out through the fruit (for example
Rhizophora,
Ceriops,
Bruguiera and
Nypa) to form a
propagule (a seedling ready to go), which can produce its own food via
photosynthesis. When the propagule is mature it drops into the water where it can then be transported great distances. Propagules can survive desiccation and remain dormant for weeks, months, or even over a year until they arrive in a suitable environment. Once a propagule is ready to root, it'll change its density so that the elongated shape now floats vertically rather than horizontally. In this position, it's more likely to become lodged in the mud and root. If it doesn't root, it can alter its density so that it floats off again in search of more favorable conditions.
Species
The following listing (modified from Tomlinson, 1986) gives the number of species of mangroves in each listed plant genus and family.
Major components
| Family |
Genus, number of species |
Common name |
Acanthaceae, Avicenniaceae or Verbenaceae
(family allocation disputed) |
Avicennia, 9 |
Black mangrove |
| Combretaceae |
Conocarpus, 1; Laguncularia, 11; Lumnitzera, 2 |
Buttonwood, White mangrove |
| Arecaceae |
Nypa, 1 |
Mangrove palm |
| Rhizophoraceae |
Bruguiera, 6; Ceriops, 2; Kandelia, 1; Rhizophora, 8 |
Red mangrove |
| Lythraceae |
Sonneratia, 5 |
Mangrove apple |
Minor components
| Family |
Genus, number of species |
| Acanthaceae |
Acanthus, 1; Bravaisia, 2 |
| Bombacaceae |
Camptostemon, 2 |
| Cyperaceae |
Fimbristylis, 1 |
| Euphorbiaceae |
Excoecaria, 2 |
| Lecythidaceae |
Barringtonia, 6 |
| Lythraceae |
Pemphis, 1 |
| Meliaceae |
Xylocarpus, 2 |
| Myrsinaceae |
Aegiceras, 2 |
| Myrtaceae |
Osbornia, 1 |
| Pellicieraceae |
Pelliciera, 1 |
| Plumbaginaceae |
Aegialitis, 2 |
| Pteridaceae |
Acrostichum, 3 |
| Rubiaceae |
Scyphiphora, 1 |
| Sterculiaceae |
Heritiera, 3 |
Geographical regions
Mangroves occur in numerous areas worldwide. See
List of mangrove ecoregions.
Africa
There are important examples of mangrove swamps in
Kenya and
Madagascar, the latter even admixed at the coastal verge with the
Madagascar dry deciduous forests. Nigeria has the largest concentration of mangroves in Africa, spanning an area of 36,000 sq km. Many of
Nigeria's mangroves have been destroyed in the last fifty years due to oil spills and leaks, destroying local fishing economy and water quality.
Americas
Mangroves are found in many parts of the tropical and subtropical coastal parts of the Americas.
United States
Because of their sensitivity to sub-freezing temperatures, mangroves in the continental
United States are limited to the coastal
Florida Peninsula (see
Florida mangroves) and south Texas.
Central America & Caribbean
Mangroves also occur on the west coast of
Costa Rica, on the Pacific and Caribbean coasts of
Nicaragua,
Belize,
Guatemala,
Honduras, and
Panama and on many
Caribbean Islands, such as
Antigua and
St. Lucia. Significant mangals include the
Marismas Nacionales-San Blas mangroves in
Mexico. Mangroves can also be found in
Puerto Rico,
Cuba, the
Dominican Republic,
Haiti,
Jamaica,
Trinidad and the Pacific coast of
El Salvador.
South America
Brazil contains approximately 26,000 km² of mangals, which is 15% of the world's total of 172,000 km².
Ecuador and
Peru also have significant areas of mangroves mainly in the
Gulf of Guayaquil-Tumbes mangroves.
Venezuela's northern Caribbean island,
Margarita, also possesses mangrove forest in the
Parque Nacional la Restinga.
Colombia also possesses large mangrove forests on both the Caribbean and Pacific coasts.
Asia
Mangroves occur on the south coast of Asia, throughout the
Indian subcontinent, in all the
southeast Asian countries, and on islands in the
Indian Ocean,
Arabian Sea,
Bay of Bengal,
South China Sea and the Pacific. The mangal is particularly prevalent in the deltas of large Asian rivers.
The
Sundarbans is the largest mangrove forest in the world, located in the
Ganges delta in
Bangladesh and
West Bengal, India. There are major mangals in the
Andaman and Nicobar Islands and the
Gulf of Kutch in
Gujarat. Other significant mangals include the
Bhitarkanika Mangroves and
Godavari-Krishna mangroves.
The
Pichavaram Mangrove Forest near
Chidambaram, South India is the second largest mangrove forest in the world. It is home to a large variety of birds—local resident, migratory resident and the pure migratory birds—and is separated from the Bay of Bengal by a lovely beach. It is one of those rare mangrove forests which has actually increased by 90% between 1986 and 2002.
There are large areas of mangroves in Oman near Muscat, in particular at Shinas, Qurm Park and Mahout Island. In Arabic, mangrove trees are known as
qurm, thus the mangrove area in Oman is known as Qurm Park.
Iranian mangrove forests occur between 25°11′N to 27°52′N. These forests exist in the north part of the
Persian Gulf and Oman Sea, along three Maritime Provinces in the south of
Iran. These provinces respectively from southwest to southeast of Iran, include
Bushehr,
Hormozgan and Sistan & Balouchestan.
In
Vietnam, mangrove forests grow along the southern coast, including two forests: the
Can Gio Mangrove Forest biosphere reserve and the
U Minh mangrove forest in the Sea and Coastal Region of
Kien Giang,
Ca Mau and
Bac Lieu province.
Australasia
In
Australasia, mangroves occur around much of
New Guinea,
Sulawesi and the surrounding islands.
Australia has mangle primarily on the northern and eastern coasts of the continent. It has approximately 11,500 km² of mangroves with occurrences as far south as Corner Inlet in
Victoria (37°45′S) and Barker Inlet in
Adelaide,
South Australia.
New Zealand also has mangrove forests extending to around 38°S (similar to Australia's southernmost mangrove incidence): the furthest geographical extent on the west coast is
Raglan Harbour (37°48′S); on the east coast, Ohiwa Harbour (near
Opotiki) is the furthest south that mangroves are found (38°00′S).
Pacific islands
Twenty-five species of mangrove are found on various Pacific islands, with extensive mangals on some islands. Mangals on
Guam,
Palau,
Kosrae and
Yap have been badly affected by development. Mangroves are not native to
Hawaii, but the Red mangrove,
Rhizophora mangle, and Oriental mangrove,
Bruguiera sexangula, have been introduced and are now
naturalized. Both species are classified as "Pest Plants of Hawaiian Native Ecosystems" by the
University of Hawaii Botany Department.
Growing mangroves
Red Mangroves are the most commonly grown of all species, used particularly in
Marine Aquariums in a
sump to reduce
proteins and other
minerals in the water. People also may grow them just for their unusual appearance, either in
Aquariums, or as ornamental plants, such as in
Japan. In
Hawaii, these plants are considered pests, while in
Florida they're heavily protected.
Destruction
The
United Nations Environment Program has estimated that a quarter of the destruction of mangrove forests stems from
shrimp farming.
Grassroots efforts to save mangroves from development are becoming more popular as the benefits of mangroves are becoming more widely known. In the
Bahamas, for example, active efforts to save mangroves are occurring on the islands of
Bimini and
Great Guana Cay.
In popular media
- The mangrove is used as a symbol in Annie Dillard's essay Sojourner due to its significance as a self-sustaining biome.
- The manga series One Piece has a forest of giant mangroves forming the Shabondy Archipelago, notable for creating a resin combined with the oxygen breathed out of the trees to create large bubbles used and manipulated by the local population for everything from transport to hotels.
Further Information
Get more info on 'Mangrove'.
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