Mangrove definition: Mangroves are woody plants and shrub that inhabit the upper intertidal zones of saltwater (30 to 90ppt) areas, primarily in tropical and subtropical coastal regions within 30° of the equator and form low diversity forests with complex food webs and unique ecosystem dynamics. Mangroves form a characteristic saline woodland or shrub land habitat, called mangrove swamp, mangrove forest, mangrove or mangal, in coastal depositional environments where fine sediments often with high organic content collect in areas protected from high energy wave action. They occur both in estuary and along open coastlines. Mangroves dominate three quarters of tropical coastlines and cover roughly 172,000 sq. km. of the earth’s surface in the large river deltas, estuaries and barrier islands.
Bakkhali – Frazergunj Mangroves over recent dunes
Mangroves occur in two distinct biogeographical regions: the Indo–West Pacific (IWP), which includes Asia, Australia, Oceana, and the eastern coast of Africa; and the Atlantic–Caribbean–East Pacific region (ACEP), which covers the America and the western coast of Africa. The IWP region contains more than three times as many genera, and roughly five times as many mangrove tree species, as the ACEP region does. Mangrove taxa, largely belonging to the plant Family Rhizophoraceae, are specialized and segregated with respect to tidal height, salinity range of soil and water and soil aeration. The landward fringe has the most variable floristic composition in wet climate.
Origin of the ‘Mangrove’: World wide Mangroves are differently called as 'mangals', 'coastal woodlands', 'tidal forests' etc. The word "mangrove" is obscurely connected with the Portuguese word "mangue" and the Spanish word "mangal" and the English word "grove" and it dates its origin as 1613. However, Marta Vannucci pointed out that the word was neither Portuguese nor Spanish and concluded that the term "mangue" derived from the national language of Senegal. It was probably adopted by the Portuguese, and later modified by the Spanish, because of their exploration of the West African coast.
Global distribution of the Mangrove Provinces
Africa - Nigeria has Africa's largest (36,000 sq. km.) mangrove forest being destroyed by oil spills and leaks in the last fifty years; Kenya and Madagascar; Egypt; the Gulf of Aqaba.
United States - Coastal zones of North, South and Central America; Florida peninsula; coast of southern Louisiana and south Texas.
Central America & Caribbean - Coast of Costa Rica; Nicaragua; Belize; Guatemala; Honduras; Panama and on many Caribbean islands; Puerto Rico; Cuba; the Dominican Republic; Haiti; Jamaica; Trinidad; Barbados and the Pacific coast of El Salvador.Nigeria has Africa's largest (36,000 sq. km.) mangrove forest being destroyed by oil spills and leaks in the last fifty years; Kenya and Madagascar; Egypt; the Gulf of Aqaba.
South America - Brazil (26,000 sq. km. of mangals); Ecuador and Peru; northern Caribbean island; Isla Margarita and Colombia.Nigeria has Africa's largest (36,000 sq. km.) mangrove forest being destroyed by oil spills and leaks in the last fifty years; Kenya and Madagascar; Egypt; the Gulf of Aqaba.
Asia - Indian subcontinent; islands in the Indian Ocean; coastal Arabian Sea and Bay of Bengal; South China Sea and the Pacific; Indus delta in Pakistan, coastal Sindh and Baluchistan, Vietnam, Kien Giang, Ca Mau and Bac Lieu Province.
Middle East - Oman; Iran near Muscat; Persian Gulf and Oman Sea.
Australia - Northern and eastern coasts (11,500 sq. km. of mangroves); New Guinea; Sulawesi; Victoria and Barker Inlet in Adelaide; Millers Landing and New Zealand and Pacific Islands
Indian Mangroves - The Sundarban is the largest mangrove forest in the world, located in India and Bangladesh. The Pichavaram Mangrove Forest near Chidambaram, South India, by the Bay of Bengal is the world's second largest mangrove forest. Mangroves are found in the Andaman and Nicobar Islands, Gulf of Kutch, Bhitarkanika and Godavari – Krishna deltas
Importance of mangroves:
Mangroves protect coastal areas from erosion, storm surge (especially during hurricanes) and tsunamis
The mangrove's massive root system is efficient at dissipating wave energy. Likewise, they slow down tidal water so that its sediment is deposited as the tide comes in, leaving all except fine particles when the tide ebbs. Mangroves protect coastal areas from erosion, storm surge (especially during hurricanes) and tsunamis
The unique mangrove ecosystem forms intricate submerged mesh of root that offers a quiet marine window to host young organisms like barnacles, algae, oysters, sea sponges and bryozoans that require a hard surface for anchoring and filter feeding. Shrimps and Thalassinidea dwel in the muddy rooted bottom. Mangrove crabs mulch the mangrove leaves, adding nutrients to the mangove muds for other bottom feeders. Export of carbon fixed in mangroves is important in coastal food webs.
Mangroves in Vietnum, Thailand, Philippines and India host several commercially important species of fish and crustaceans
The fine, anoxic sediments under mangroves act as sinks for a variety of heavy metal in the sediments scavenged from the water.
Red mangroves are being cultivated in Japan for use in marine aquariums in a sump to reduce proteins and other minerals in the water.
Evolution of Mangrove: - Mangroves evolved around 114 MY ago. The Indo-Malaysian region is considered to be the cradle of evolution of mangrove ecosystem as there are far more mangrove species present in this region than anywhere else. The mangrove plants then spread to other tropical regions through their unique floating propagules and seeds. These early mangroves, borne by ocean currents, spread westward to India and East Africa, and eastward to the Americas, arriving in Central and South America during the upper Cretaceous period and lower Miocene epoch, between 66 and 23 MY ago. During that time, mangroves spread throughout the Caribbean Sea across an once existed open seaway where Panama lies today. Later, sea currents propagated mangrove seeds to the western African coast and far south to New Zealand. This explains why the mangroves of West Africa and the America contain fewer, but similar colonizing species, whereas those of Asia, India, and East Africa contain a much fuller range of mangrove species. Presently, the Indo-Pacific region is known for its luxuriant mangroves. The Sundarbans of India and Bangladesh form the world’s most colossal mangrove delta complex
Sundarban mangrove forest, Sajnekhali
Sundarban creek banks with mangroves, near Gosaba
Mangrove distribution vs Pleistocene glaciations: - Mangroves evolved around 114 MY ago. The Indo-Malaysian region is considered to be the cradle of evolution of mangrove ecosystem as there are far more mangrove species present in this region than anywhere else. The mangrove plants then spread to other tropical regions through their unique floating propagules and seeds. These early mangroves, borne by ocean currents, spread westward to India and East Africa, and eastward to the Americas, arriving in Central and South America during the upper Cretaceous period and lower Miocene epoch, between 66 and 23 MY ago. During that time, mangroves spread throughout the Caribbean Sea across an once existed open seaway where Panama lies today. Later, sea currents propagated mangrove seeds to the western African coast and far south to New Zealand. This explains why the mangroves of West Africa and the America contain fewer, but similar colonizing species, whereas those of Asia, India, and East Africa contain a much fuller range of mangrove species. Presently, the Indo-Pacific region is known for its luxuriant mangroves. The Sundarbans of India and Bangladesh form the world’s most colossal mangrove delta complex
Sunderban Mangrove delta complex: - Sundarbans, a cluster of 102 miracle islands, form the largest mangrove delta complex on the globe in the estuarine phase of the Ganges and Brahmaputra Rivers, constitute a unique Biosphere Reserve in the coastal Bay of Bengal and host landmark ancient heritage of mythological and historical events bestowed with wide bio-diversity of mangrove flora and fauna, magnificent scenic beauty and natural resources of immense scientific, anthropological and archaeological interests. This region is one of the world’s most remotely challenged geographical regions with a population density of more than 1100 person per sq. km.
Etymology: - "Sundarban" literally means "beautiful jungle or forest" in Bengali language. The name Sundarbans may also have been derived from the Sundari trees that are omnipresent in Sundarbans. Other possible explanations can be a derivation from "Samudra Ban" (Sea Forest) or "Chandra-bandhe" (name of a primitive tribe). However, the generally accepted view is attributed to Sundari trees.
History: - The history of Sundarbans can be traced back to 200-300 AD. A ruin of city built by Chand Sadagar has been found in the Baghmara Forest Block. During the Mughal Empire, Raja Basant Rai took refuge in the Sundarbans from the advancing armies of Emperor Akbar. Many of the buildings built by them later fell to the hands of Portuguese pirates, salt smugglers and dacoits in the 17th century. Evidence of the fact can be traced from the ruins at Netidhopani and other places scattered all over Sundarbans.
During the Mughal period (1203-1538), the local kings leased the forests of the Sundarbans out. It acquired the distinction of being the first mangrove forest in the world to be brought under scientific management. The area was mapped by the Surveyer General as early as 1764 and the proprietary rights were obtained from the Mughal Emperor, Alamgir II, by the Honorable East India Conpany in 1757. Systematic management of the forest started in 1869 after the establishment of a Forest Management Division in the Province of Bengal, in British India.
The Sundarbans was declared a reserved forest in 1875-76, under the Forest Act, 1865. A Forest Division was created in 1879 with headquarters in Khulna. The first management plan was written for the period 1893-98.
In 1911, it then stretched for about 266 km from the mouth of the Hugli to the mouth of the Meghna, and was bordered inland by three districts: Twenty-four Parganas, Khulna and Backergunj. The total area including water was estimated to be 16,902 sq km.
Five feathers in the cap:
Sundarban, the largest deltaic mangrove forest in the world, consists of 10,200 sq km area of which 5937 sq km and 4263 sq km of Reserve forests spread respectively over Bangladesh and India. In India, 1678 sq km and 2585 sq km forest areas constitute South 24 Parganas Reserve Forest and Sundarban Tiger Reserve respectively
Sundarban Tiger Reserve [STR] was constituted by Govt. of India under “Project Tiger” scheme , in 1973 . It was declared as a Wildlife Sanctuary in 1977 The entire forest area falling in the West Bengal State of India has been dubbed as Sundarbans National Park in 1984
Considering the importance of Sundarban's Bio-geographic Region, the National Park Area of the Sundarban Tiger Reserve has been included in the list of World Natural Heritage Sites in 1987
The Govt. of India declared the Sundarban region including the protected area of Sundarban Tiger Reserve as Biosphere Reserve in 1989. And it received the recognition of UNESCO under its Man & Biosphere (MAB ) Programme in Nov. 2001.
Sundarban Reserve Forest has been nominated for recognition as a Ramsar Site (A Wetland of International Importance)
Sundarban forest, near Gosaba
Sunderban Mangrove Ecology
Mangroves are able exploiter of intertidal saline habitats - by developing physiological adaptations to overcome the problems of anoxia, high salinity, intense sunlight and frequent tidal inundation. Each species has its own solutions to these problems; this explains why, across the shoreline, Rhizophora show distinct zonation
Biology: - Of the recognized 110 mangrove species of Sundarbans, only 54 species in 20 genera from 16 family constitute the "true mangroves", species that occur exclusively in mangrove habitats.The species that demonstrate convergent evolution find similar solutions to the said problems of tropical conditions and hence form natural associations.
Adaptations to low oxygen: - Rhizophora mangal surviving in the most inundated areas can prop themselves above the water level with stilt roots that absorb air through pores in their bark. Avicennia germinans live on higher ground and make many pneumatophore, a specialized root-like structure, which stick up out of the soil like breathing straw tubes of even 3m height. The roots also contain wide aerenchyma to facilitate oxygen transport within the plant.
Limiting salt intake: - Red mangroves have significantly impermeable roots and can exclude sodium salt by ultra-filtration mechanism from the rest of the plant. They can store salt in cell vacuole. White (or grey) mangroves can secrete salts directly through salt glands at leaf base.
Limiting water loss: -Because of the limited freshwater availability in salty intertidal soils, mangroves limit the amount of water that they lose through their leaves. They can restrict the opening of their stomata and change the orientation of their leaves to avoid the harsh midday sun to reduce evaporation from the leaves
Nutrient uptake: - The biggest problem faced by the mangroves is nutrient uptake. Because the soil is perpetually waterlogged, there is little free oxygen. Anaerobic bacteria liberate nitrogen, soluble iron, inorganic phosphate, sulphide and methane making the soil much less nutritious and contribute a pungent odor to mangroves. Prop root systems 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 during submerged condition during high tides.
Increasing survival mechanism of mangrove offspring: - In harsh environment, mangroves have evolved a special mechanism that helps their offspring survive. Mangrove seeds are buoyant and hence suited to tidal-water dispersal. Unlike most soil germinating plants, many mangroves (e.g. Red Mangroves) are vivipary, whose seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit or out through the fruit to form propagules (a ready-to-go seedling) that produce their own food via photosynthesis. The mature propagule then drops into the tidal water and get transported to great distances. Propagules can survive desiccation and remain dormant for over years before arriving at a suitable environment.
Sundarban Bio-Sphere Reserve: Special features
Sundarbans is the only mangrove tiger land on the globe
Sundarban mangrove forests comprising of more than 60% of total Indian mangrove form the largest nursery for fish and shell fishes and are responsible for the coastal fishery of the whole of eastern India.
Mangrove plant association of Sundarbans exhibit the more generic/species diversity than any large mangrove reserve on the earth.
Sundarban harbors a good number of endangered plants and animals, e.g., the Bengal Tiger, Estuarine crocodile, fishing cat, Salvador Lizard, Gangetic Dolphin, Batagur (river terrapin), Marine turtles, horseshoes, etc.
It saves Calcutta and neighboring metropolises from annual low pressure catastrophes, acting as an effective wind barrier
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