Above and below water view at the edge of the ''mangal''.
'Mangroves' (generally) are
plants 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'''
[1], 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''. Mangal is found in depositional coastal environments where fine sediments, often with high organic content, collect in areas protected from high energy wave action.
Ecology
A 'mangal' is a plant community and habitat where mangroves thrive
. They are found in tropical and sub-tropical
tidal areas, and as such have a high degree of salinity. Areas where mangals occur include
estuaries and marine shorelines.
Plants in mangals are diverse, but all are able to exploit their habitat (the
intertidal zone) by developing physiological adaptations to overcome the problems of
anoxia, high
salinity and frequent tidal
inundation. About 110 species have been identified as belonging to the mangal.
[2] 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 variantions 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 is 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.
[3][4] Their massive root system is efficient at dissipating wave energy.
[5] Likewise, they slow down tidal water enough that its sediment is deposited as the tide comes in and is not re-suspended when the tide leaves, except for fine particles.
[6] As a result, mangroves build their own environment.
Because of the uniqueness of the mangrove ecosystems and their protection against erosion, they are often the object of conservation programs including national
Biodiversity Action Plans.
Despite their benefits, the protective value of mangroves is sometimes overstated. Wave energy is typically low in areas where mangroves grow,
[7] so their effect on erosion can only be measured in the long-term.
Their capacity to limit high-energy wave erosion is limited to events like storm surges and tsunamis.
[8] 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. 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.
Mangrove crabs improve the nutritional quality of the mangal muds for other bottom feeders by mulching the mangrove leaves.
[9] 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 crustacea. 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 the world's mangroves have been lost n recent times.
Biology
A red mangrove, ''Rhizophora'' sp.
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
.
Convergent evolution has resulted in many species of these plants finding similar solutions to the problems of variable salinity, tidal ranges (inundation),
anaerobic soils and intense sunlight that come from living in the tropics. Plant biodiversity is generally low in a given mangal -- more than 20 species are uncommon.
This is especially true in higher latitudes, and in the Americas. The greatest biodiversity occurs in the mangal of
New Guinea,
Indonesia and
Malaysia.
[10]
; 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 30 centimeters, and in some species over 3 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.
Salt crystals formed on grey mangrove leaf
; 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 have 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.
[11]
; Nutrient uptake
The biggest problem that mangroves face is nutrient uptake. Because the soil is perpetually waterlogged, there is 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 mechnanism 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 (e.g. Red Mangrove) are viviparous, i.e., their seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit (e.g. ''Aegialitis, Acanthus, Avicennia'' and ''Aegiceras''), or out through the fruit (e.g. ''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 will change its density so that the elongated shape now floats vertically rather than horizontally. In this position, it is more likely to become lodged in the mud and root. If it does not 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 50 years due to oil spills and leaks, destroying local fishing economy and water quality.
[ Curse of the Black Gold, O'Neill.T, , , National Geographic, 2007 ].
Americas
Mangroves are found in many parts of the tropical and subtropical coastal parts of the Americas.
North America
Because of their sensitivity to sub-freezing temperatures, mangroves in the continental
United States are limited to the coastal
Florida Peninsula (see
Florida mangroves).
Central America & Caribbean
Mangroves also occur on the west coast of Costa Rica,
on the Pacific and Caribbean coasts of Nicaragua 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,
Dominican Republic,
Haiti and
Jamaica.
South America
★
Brazil: contains approximately 26,000 km² of mangel, 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.
★
Colombia: also possesses large mangrove forests on both Caribbean and Pacific coasts.
The mangrove species ''Sonneratia'', showing abundant
pneumatophores, growing on the landward margin of the reef flat on
Yap.
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.
[12] Other significant mangals include the
Bhitarkanika Mangroves and
Godavari-Krishna mangroves.
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 Province biosphere reserve.
New Guinea and environs
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
Australia. Australia has approximately 11,500km² of mangroves with occurances as far south as Corner Inlet in
Victoria and Barker Inlet in
Adelaide,
South Australia.
[13]
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.
[14] Mangroves are not native to
Hawaii, but the Red mangrove, ''
Rhizophora mangle'', and Oriental mangrove, ''
Bruguiera sexangula'', have been introduced and are now
naturalized.
[15] Both species are classified as "Pest Plants of Hawaiian Native Ecosystems" by the
University of Hawaii Botany Department.
[16]
Destruction
The
United Nations Environment Program has estimated that a quarter of the destruction of mangrove forests stems from
shrimp farming.
[17]
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.
Notes
1. Hogarth, Peter J. (1959). ''The Biology of Mangroves'' Oxford University Press, Oxford.
2. Mangal (Mangrove). ''World Vegetation''. Mildred E. Mathias Botanical Garden, University of California at Los Angeles
3. Mazda, Y.; Kobashi, D. and Okada, S. (2005) "Tidal-Scale Hydrodynamics within Mangrove Swamps" ''Wetlands Ecology and Management'' 13(6): pp. 647-655
4. Danielsen, F. ''et al.'' (2005) "The Asian tsunami: a protective role for coastal vegetation" ''Science'' 310: p. 643.
5. Massel, S. R.; Furukawa, K.and Brinkman R. M. (1999) "Surface wave propagation in mangrove forests" ''Fluid Dynamics Research'' 24(4): pp.219-249
6. Mazda, Yoshihiro et al. (1997) "Drag force due to vegetation in mangrove swamps" ''Mangroves and Salt Marshes'' 1: pp.193-199
7. Baird, Andrew (26 December 2006) "False Hopes and Natural Disasters" ''New York Times'' editorial
8. Dahdouh-Guebas, F. ''et al.'' (2005) "How effective were mangroves as a defence against the recent tsunami?" ''Current Biology'' 15(12): pp. 443-447
9. Skov, Martin W. and Hartnoll, Richard G. (March 2002). Paradoxical selective feeding on a low-nutrient diet: why do mangrove crabs eat leaves? ''Oecologia'' 131(1): pp. 1-7.
10. UN Report on mangrove diversity.
11. Calfo, Anthony (2006). ''Mangroves for the Marine Aquarium''.
12. Mangroves of India - URL retrieved November 26, 2006
13. State of the Marine Environment Report for Australia, , Leon P., Zann, Australian Government, Dept of Environment and Heritage, , ISBN
14. Hawaii and the Pacific Islands
15. Allen, James A. and Krauss, Ken W. (2006) "Influence of Propagule Flotation Longevity and Light Availability on Establishment of Introduced Mangrove Species in Hawai'i". ''Pacific Science'' 60:3, July 2006. Abstract at [1] - URL retrieved November 28 2006.
16. Hawaiian Alien Plant Studies - URL retrieved November 28 2006.
17. Botkin, D. and E. Keller (2003) ''Enrivonmental Science: Earth as a living planet'' (p.2) John Wiley & Sons. ISBN 0-471-38914-5
See also
★
Body of water
★
Salt marsh
★
Wetland
References and external links
★ Saenger, Peter (2002). ''Mangrove ecology, silviculture, and conservation''. Kluwer Academic Publishers, Dordrecht. ISBN 1-4020-0686-1.
★ Hogarth, Peter J. (1999). ''The Biology of Mangroves''. Oxford University Press, Oxford. ISBN 0-19-850222-2.
★
Thanikaimoni, Ganapathi (1986) ''Mangrove Palynology''
UNDP/
UNESCO and the French Institute of
Pondicherry, ISSN 0073-8336 (E).
★ Tomlinson, Philip B. (1986). ''The Botany of Mangroves''. Cambridge University Press, Cambridge, ISBN 0-521-25567-8.
★ Teas, H. J. (1983). ''Biology and ecology of mangroves''. W. Junk Publishers, The Hague. ISBN 90-6193-948-8.
★ Plaziat, J.C., et al. (2001). History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record. ''Wetlands Ecology and Management'' 9 (3): pp. 161-179.
★ Sato, Gordon, et al.
Growing Mangroves With The Potential For Relieving Regional Poverty And Hunger WETLANDS, Vol. 25, No. 3 - September 2005
★ Jayatissa, L. P., Dahdouh-Guebas, F. & Koedam, N. (2002). A review of the floral composition and distribution of mangroves in Sri Lanka. ''Botanical Journal of the Linnean Society'' 138: 29-43.
★ Warne.K, (February 2007). Forests of the Tide. ''National Geographic'' pp. 132-151
★
Tsunami protection.
★
The story of the UNESCO Mangrove Programme.
★
Science and Management of Mangroves in the South China Sea and the Gulf of Thailand.
★
WWF article about the mangrove biome.
★
East African Mangroves, a website managed by the Universities of Brussels (Belgium) and Florence (Italy).
★
Kenyan Mangroves.
★
Large mangrove website.
★
Borneo Mangroves.
★
Sundarbans Tiger Project Research and Conservation of tigers in the largest remaining mangrove forest in the world.
★
Coastal wetland and shoreline change mapping of Pichavaram, south east coast of India using Satellite data.
★
Status of Indian Mangroves: Pollution Status of Pichavaram Mangrove, Southeast Coast of India.
★
Mangrove Action Project. Advocacy group devoted to the conservation, restoration and sustainable management of mangroves and related coastal ecosystems. Spun off from
Earth Island Institute in March 2007.
★
Global Mangrove database and Information System (GLOMIS).
★
Information and photo of Red Mangrove in aquarium - ''Rhizophora mangle''.
★
Mangroves of Rodrigues Island.
★
Mangroves of Singapore.
★
mangrove.org - Mangrove Afforestation, Habitat Creation, Replenishment, Shoreline Stabilization.
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