The mangrove is a grouping of mainly woody plants which develop in the zone of swinging of the tides called Estran of the low coasts of the tropical areas . One finds also Marais with mangroves with the mouth of certain rivers. These particular mediums get important resources (forest and halieutics) for the populations living on these coasts. The mangroves are the most productive ecosystems in biomass of our planet. The woody species most notable are the Palétuvier S with their pneumatophorous and their stilt roots.
The fast degradation of some mangroves became worrying because they constitute effective stabilizers for certain fragile coastal areas which are now threatened, and because they contribute to the ecological Résilience of the ecosystems after the Cyclone S and Tsunami S.
Geographical distribution or chorology
The mangrove develops on the littoral in calm and not very major zones. It occupies the three-quarter of the coasts and deltas of the tropical areas ensuring an excellent protection against the erosion and even the Tsunami S. It covers a surface of approximately: 150000 km ² on our planet. It is located along the coastal areas between the parallel 30° Northern and Southern, that is to say the equatorial zones:
- In Africa:
- In East Africa: south of Somalia in Mozambique one can observe a dense and high mangrove of about fifteen meters.
- In north, on the edges of the Red Sea and the Indian Ocean, it is already less dense and makes nothing any more but 5 meters.
- In West Africa one can observe some in the Golfe of Guinea.
- has Madagascar.
- In Asia one can observe mangroves in the islands more in the South (Îles Yaeyama) of the Japan like in Southeast Asia including almost all the islands separating the Asia from the Australia.
- the greatest whole of mangrove of the world is the delta of the Gange and the Brahmapoutra.
- In South America, the mangrove is quasi omnipresent on the Northern littoral of the continent. Like in the South of the Central America until in Ecuador.
The type corresponding of biome in the moderate zones is the saline Marais.
FaunaMany species of birds populate the mangrove; but the crabs, the molluscs, the crustacean and the fish are most present. They all are amphibious. A typical fish of the mangroves, the Périophtalme developed fins enabling him to leave water and to move. It can live during long periods out of water. One finds Crabe S like Uca and Mantous, or the crab " sémaphore" known as also violonist. This nickname is given to him because of the Pince which it positions on the Abdomen. The air zone is occupied by insects, reptiles and birds.
With the Bangladesh, the mangrove is the refuge of the Bengal tiger. It is one of the last territories where the man cannot threaten it. But one finds there also the Cerf axis, of the Macaque S whose tangle of branches of trees offers an impenetrable refuge. The forests of mangrove are also the place of dwelling of many birds like the red Ibis on the Trinidad.
FloraThe evolution caused a convergence of the vegetable solutions of the plant of the mangroves to the problems of the variable Salinité, variations of the Marée S (flood), grounds without oxygen and of the intense sunlight of the life in the tropics. The plants developing in the mangrove must thus be adapted to a hostile environment:
- a high salinity
- Of the immersed roots
- a weak oxygenation of the ground due to the vase
- an unstable ground
- Of the warm water
The mangroves are the principal plant species of the mangrove. They knew to adapt to a constraining medium.
Adaptation to a high salinityThe trees tolerate very well the rate of high salt of Mangrove. It is said that these plants are Halophile S. For example, the red mangroves isolate oneself from salt by having impermeable roots which strongly tubérisent, thus acting like a mechanism of ultrafiltration to filter the salt of the medium. The water of the medium contains up to 90%, and in certain cases up to salt 97%. All the salt which returns in the plant accumulates in the growths and is concentrated in old women Feuille S who are used then as hangar, storage distant in the Vacuole S from the vegetable cells. The white mangroves (or gray) can secrete salt via glands with salt at the base of the sheets (what gave them their name since they are covered with white salt crystals).
Adaptation to a weak oxygenation of the groundThe ground of Mangrove consists of littoral Vase, a medium completely Anaérobie (without oxygen). The Respiration of the trees is thus ensured thanks to complex bodies developed in the root S. For example, the red mangroves, which can live in the most flooded sectors, push to the top above the level of water with root S stilts. They can recover the air by slits in their bark called lenticels. The black mangroves live on higher grounds and produce many Pneumatophore S (of the specialized roots which pushes out of the ground upwards as straws for breathing) which are covered with lenticels. These " tubes for respirer" sizes of 30 centimetres reach, although some species have some which reach more than 3 meters in height. There are four types of pneumatophorous: stilt, right, in arch and ribbon.
Limitation of the water lossesBecause of the availability limited out of fresh water in the salted grounds of the mangrove, the mangroves developed mechanisms to limit the quantity of water which they lose by their sheets. Their sheets can to control opening of their Stoma S (of the small pores on the surface of their sheets which exchanges gases and steam during the Photosynthèse) and also to control the orientation of their sheets. By directing their sheets to avoid the sharp sun of midday, the mangroves can reduce the evaporation to surfaces of their sheets.
Recovery of nutrientsThe biggest problem to which the mangroves face is the recovery of the Nutriment S in the medium. As the ground in leque the mangroves live is perpetually saturated with water, there is not many Oxygène free available. With these low oxygen contents, the anaerobic bacteria produce Azote in gas form, of the soluble Fer, the inorganic Phosphate S, the Sulfure S and the Méthane, which contribute to the odor unpleasant of the marshes to mangroves and returns hostile environment to the plant species. Since the ground is not particularly nutritive, the mangroves adapted by modifying their roots. The systems racinaires in the shape of stilt make it possible the mangroves to directly recover gases atmosphere and various other food, like iron, of the inhospitable ground. They often store gases directly inside the roots so that they can be fed all the same when the roots are submerged during the high tide.
Adaptation on the groundIn addition to their respiratory role, the roots have an important role of fixing of course. They make it possible the plant to ensure its fixing on the ground made up of Vase S not very stable. The mangroves avoid the erosion coasts thanks to their roots forming a rampart with the waves and making it possible to retain the alluvia coming from the rivers.
Evolution of the young seedlingsIn this hard environment, the mangroves evolved/moved to propose a mechanism of assistance to the young seedlings. All the mangroves have Graine S floating which support the Dispersion by water. With the difference of the majority of the plants, whose seeds germinate in the ground, much of mangroves (for example red mangrove) are Vivipare S i.e. their seeds germinate on the tree relative before falling. Once the seed germinated, the seedling develops in the fruit (for example Aegialitis, Acanthus, Avicennia and Aegiceras), or towards outside while making use of the fruit like support (for example Rhizophora, Ceriops, Bruguiera and Nypa). One names this last system a propagule (a plant ready to go), which can produce its own food via the Photosynthèse. When the propagule is ripe, it falls in water where it can be transferred onto long distances. There can survive the Dessication and remain dormant lasting of the weeks, of the months, or even a year until it arrives in a suitable environment. Once a propagule is ready with enraciner, it will change its density so that instead of making a horizontal system racinaire supporting the floating, it produces a vertical system racinaire. In this position, it is ready enraciner in mud. If a propagule enracine not, it can change its density so that it floats still further with research from more favorable conditions.
Species adapted to the medium
For these reason, rare are the species of trees which adapted to this medium; it is:
- the Mangrove S
- the gilded Fern
- the yellow Manglier ( Avicennia )
- the red Manglier ( Rhizophora )
OrganizationOne notes 4 Palétuvier S standards almost always present in a mangrove:
- Rizophora mangrove or red mangrove
- Avicenia germinans or black mangrove
- Laguncularia racemosa or white mangrove
- gray Conocarpus erectus or mangrove
Each one of these mangroves pushes in a given place:
- the red mangrove, least resistant to salinity, develops in seaside.
- the black mangrove develops just behind followed mangroves white.
- comes then the pond drink deprived of vegetation because of the too great salinity of its ground.
- finally develops the gray mangroves which are not adapted to the immersion but which supports a very high salinity.
A traditional resourceIn many countries, the mangrove is a place of harvest and traditional use of products used by the local population. In Bangladesh, the mangrove produces Bois for the coal, but also for constructions of dwelling. It provides also the Miel and of many plants which feed the Artisanat and the local Pharmacopée.
A threatened mediumThe mangroves are mediums threatened primarily by human constructions seeking to gain on the sea and the coasts. Thus, they are replaced by saline Marais S, basins of Aquaculture or roads. They are also sensitive to chemical pollution or the oil slicks.
But the greatest threat of the mangrove is the breeding of shrimps which is established massively in seaside. Indeed, for several years, the shrimp has been a consumable running in the Western countries and the tropical countries are the ideal places for its breeding. The littoral occupied by the mangrove is replaced little by little by basins of breeding which are generally abandoned after a few years of breeding in order to avoid the appearance of diseases.
That causes to prevent the local inhabitants from continuing to collect in a traditional way the products of the mangrove. Certain badly built basins caused infiltrations in the ground water causing its salinisation and making its water unfit for consumption.
See also: breeding crevettes#Effets_environnementaux
Moreover, the mangrove plays a big role in the fixing of carbon. A specialist in the maritime mediums, Jin Eong Ong, made a study on the quantity of carbon captured by the mangrove. He proved that this ecosystem is that which produces the most Carbone Net, approximately 110 kg per hectare and day. Its destruction would thus have an impact on the climatic Dérèglement and the quantity of carbon slackened in the atmosphere.
Relation with the others biosystèmesThe mangrove is very related on the Herbier (or Littoral) and to the Récif S. Indeed, it has need to develop of a calm water, stripped of swell. It is the Récif, by breaking the Houle, which protects and offers to the mangrove a favorable Environnement. But, the mangrove is also an excellent barrier between the violent ocean and the fragile coast, particularly during the hurricanes, which can cause a sudden rise of water on the shores. The system racinaire of the mangroves is completely effective to absorb the energy of the waves. Thus, the mangrove is an excellent protection vis-a-vis the Tsunami and appreciably reduces the destruction caused to the back of this protection zone. Since the catastrophe of the Tidal wave of December 2004, this asset of the mangrove was proposed for the protection of the coasts. With the Bangladesh, the government tries to develop the culture of the mangrove in order to stabilize the coasts and to gain grounds on the delta of the Gange.
N the other hand, the mangrove filter and stabilizes the Sédimentation, avoiding with the reefs being covered with Vase and thus decaying. These systems racinaires also prevent the coastal erosion. The water run-off of the tides is slowed down rather appreciably so that the sediments settle with the foot of the roots of the mangroves. Consequently, the mangroves maintain their own environment. It is also noted that these three Biosystème S: mangrove, Herbarium and Reef S, play each one a role in the development of the fauna:
- the Poisson S are born with the shelter in the mangrove and hide there during their development
- once too large to hide in the mangrove, they hide in the Herbier where they are still protected by the Récif.
- they live adult once in the reefs or beyond that.
The mangroves are at the base of single ecosystems, particularly around their complex systems racinaires. Where the roots are permanently submerged, the mangroves are the hosts of Algue S, of Bernacle S, Huître S, sponge S and of Cnidaire S. They require all of the hard substrates to be anchored while they filter their food.
Biogeographic equivalencesThere exist equivalents of the mangrove in the more distant latitudes: they are the Herbus, one can observe some on bay of the Mont Saint-Michel like on the coast of Picardy.
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