Mangroves are often called coastal bioshield because of its crucial role in the ecological system. They provide a safe refuge for aquatic organisms, protects mankind from storm surge, and secures economic livelihood of coastal communities. At the same time, mangroves significantly facilitates in moving organic matter and energy from the land to marine ecosystems.
What are mangroves?
Mangroves are those plants that thrive along coastlines, lagoons, and estuaries in the tropics and sub-tropical regions. These salt-tolerant plants make significant socio-economic and environmental contributions as they protect the coastal and inland areas from severe conditions, like erosion, wind, waves, water currents, tsunamis, and storm surge.
Mangrove plants are classified into two groups, namely:
- The true or exclusive mangroves species. This refers to those species that grow only in mangrove environment. They are physiologically, morphologically, and reproductively adapted to waterlogged, saline, and anaerobic condition. You’d never find them extending into terrestrial plant community.
There are 110 recognized mangrove species, but only about half of it are considered true or exclusive mangrove species. The rest belong to the second group.
- The associated species. This refers to the plants that grow in terrestrial environment, and; pure halophytes, or those plants growing only in salty water.
Mangroves used to cover three-fourths of the world’s coastlines before they were exploited for timber for building construction, boat-making, and fuel wood for heating and cooking. Southeast Asia hosts the greatest diversity, while the Americas is home to only 12 species. These plants grow in varied sizes, from small bushes to the 60-meter giants, which are found in Ecuador.
Roles of mangroves to the ecosystem
Mangroves, or mangrove forests, are highly valuable ecosystem that provide a thousand and one benefits to humans, other living organisms, and the environment.
Coastal stabilization. Its dense root systems
- dissipate waves by absorbing wave energy and reducing water velocity
- trap sediments carried by incoming currents and high tides
- control water flow
- serve as important catalyst in reclaiming land from the sea; thus, contributing to land building
- stabilizes the substrate and the coastline
- prevent uncontrolled shifting of the coastline sand
Maintain coastal water quality. By its abiotic and biotic retention ability, and cycling of nutrients, pollutants and particulate matter, mangroves effectively purify and preserve water quality in coastal areas. They also protect rivers and streams from pollution. Because of this, mangroves are now used for treatment of aquaculture and receiving areas of sewage effluents.
Coral reef protection and nutrients source. Since they filter out sediments, mangroves significantly protect coral reefs and seagrass beds from being smothered in such deposits, as well as keep shipping paths safe from siltation. Mangroves also sustain coral reefs and seagrass with necessary nutrients for its production and general health.
Habitat of aquatic animals and fisheries, and wildlife refuge. A mangrove forest is home to a large variety of shrimps, fish, crab, mollusk species, and many wildlife species of birds, mammals, honey bees, reptiles, amphibians, commercial fish and crustaceans. Its roots and branches are perfect shelter for varied animals, including many migratory species.
Mangroves provides safe rookeries, or nesting places for coastal birds like the roseate spoonbills and pelicans, and; set a perfect nursery for many fish species, including the coral reef fish.
Help against climate change and slow down global warming. Its strong root systems act as bioshields, reducing the impact of severe conditions that approach the shores like storm surge, hurricanes, wind, landslide, and erosion. Thus, protecting people living near the shores and keeping properties and structures, like sea wall, boats, and buildings from damage. Mangroves also prevent entry of excess water into farm lands that can potentially destroy productivity or land use.
Mangroves can clear away and keep greenhouse gases from the earth’s atmosphere. They remarkably contribute in minimizing carbon dioxide in the air.
Food source and livelihood for coastal communities. These fisheries serve as an essential source of food and income among people living in coastal areas.
Tourism. The diversity of life in mangrove systems and its proximity to coral reefs and sandy beaches make these areas an instant tourism destination. And as they draw tourists, divers, snorkelers, as well as scientists and students, mangroves indirectly pave the way for other businesses to flourish in its surroundings.
Useful products. Mangrove wood makes a suitable material for construction, furniture and other household item-production; telephone poles; heating, and; cooking because it is resistant to rot and fungi, and borer attacks. While some sectors harvest mangrove forests for wood chip, pulp, and charcoal production, local residents near mangrove areas find certain mangrove species medicinal and good fodder source for their animals. (More on this later)
A mangrove forest is usually composed of a few different species occupying particular niches. But you cannot expect to find all species in any given mangrove. Plants that are tolerant to tidal soakings thrive in the open sea, sheltered bays, and on fringe islands; while, those that are adapted to drier and saltier soil grow farther away from the shoreline. You can also find mangroves inland along riverbanks where freshwater current meet with sea tides.
Many of us, including me, are not familiar with the names or species of trees and plants that grow in mangroves. And so, for the benefit of us all, let me share with you some of the species.
Avicennia marina. This specie is commonly called the grey mangrove or white mangrove. It belongs to the Acanthaceae plant family, which was formerly classified in the Verbenaceae or Avicenniaceae group, and thrives in intertidal zones of estuaries.
You will recognize this specie for its yellowish-green leaves, small and fragrant pale-yellow flowers, heart-shaped fruit, and pencil-sized peg type above-ground roots.
Bruguiera cylindrica. Known by its common name, small-leafed orange mangrove and Bakau Putih in Malay language, the Bruguiera cylindrica specie grows in swamps in Southeast Asia. It belongs to the Rhizophoraceae plant family, and also known for its other names, Rhizophora cylindrica, Rhizophora caryophylloides, and Bruguiera caryophylloides.
This small, erect, evergreen specie has a lanceolate-shaped, long, shiny and dark green leaves with knee-like above-ground breathing roots. Its small flowers are white, and its scaly-bottomed bark is light to dark grey or pale pink in color.
Bruguiera gymnorrhiza. Belonging to the Rhizophoraceae plant family, this specie is known for the common names Oriental mangroves, Large-leafed mangroves, and Black mangroves.
Each tree is small to moderate in size with simple, leathery, dark green leaves. Its bark is thick, hard and rough that comes in pale grey or reddish-brown color. The black mangrove is a protected specie in South Africa.
Bruguiera sexangula. Commonly called as the Upriver Orange Mangrove, this shrub belongs to the Rhizophoraceae plant family. It is also known by its synonyms, Rhizophora sexangula and Bruguiera eriopetala.
This single-stemmed, multi-branched mangrove is characterized by yellow-green leaves with shorter stalks compared to that of the Bruguiera gymnorrhiza. Its flowers have pale yellow-green to pinkish-orange calyx with 10 to 14 lobes, and white or brown 10 to 12 bi-lobed petals. Its bark comes in smooth, grey-brown shade.
Ceriops tagal. This is another specie belonging to Rhizophoraceae family and known by its synonyms, Ceriops candolliana, and Rhizophora tagal. Its common name is Yellow mangrove. But it is also called as the Indian mangrove; Indiese wortelboom in Afrikaans, and; Isinkaha in Zulu languages, respectively. This is a protected specie in South Africa.
The specie is an evergreen tree with shiny and inverted egg-shaped dark green leaves. Its bark comes smooth and pale grey to reddish brown when it’s still young; and turns deeply fissured and flaky at the bottom as it grows older. It is also characterized by a knobby above-ground roots.
Excoecaria agallocha. This belongs to the Euphorbiaceae family. Because it is a prolific specie that can be found in mangrove swamps from northwest India to Australia, Excoecaria agallocha has earned varied common names including, blinding tree, blind-your-eye mangrove, river poison tree, milky mangrove, and Thillai, mostly referring to its blinding or poisonous nature.
This specie is recognizable for its shiny, leathery with pointed tips and sharp toothed-edged leaves. The leaves are pinkish that gradually turns to green and, eventually, to bright red when it’s about to fall off. But what makes it distinct from the other species is that it exudes a milky sap when its branches or leaves break, or when the bark is damaged. The sap can cause intense pain and blistering when it comes in contact with your skin. Or worse, it can cause temporary blindness if the sap gets into your eyes.
Heritiera littoralis Aiton. Belonging to the Malvaceae family, the Heritiera littoralis Aiton is commonly known as the looking-glass mangroves. This is a medium to large evergreen tree. You will easily recognize this specie for the silvery scales on the underside of its leaves. Its bark is greyish, scaly, and fissured; while its wood is remarkably tough that locals use it as a material in boat-building.
Lumnitzera racemosa Willd. This specie, which belongs to the Combretaceae family and named after the German botanist Stephan Lumnitzer, is commonly known as the Black mangrove. Its presence is widespread and common in South Asia, Australasia, East Africa, and the Middle East, but its population has been declining over the years due to coastal development.
You usually find this black mangrove in upstream zones in the middle to high intertidal areas, and also along sandy beaches.
Pemphis acidula. Commonly known as the Iron wood, Pemphis acidula is a member of the Lythraceae plant family. This specie is not very common, but its presence is far ranging from eastern Africa, Indian Ocean coastlines, to the Pacific regions.
The iron wood specie is a slow growing shrub with no prominent aerial roots. Its lower branches are persistent and rigid and the twigs are angular and hairy.
Rhizophora apiculata Bl. This is a specie belonging to the Rhizophoraceae plant family. It is commonly found in Australia, Guam, India, Philippines, Thailand, Indonesia, Taiwan, New Caledonia, Papua New Guinea, Malaysia, Micronesia, Singapore, Solomon Islands, Sri Lanka, Maldives, Vanuatu, and Vietnam. In the Philippines, this specie is called bakhaw lalaki.
Its leaves are narrowly elliptic, apiculate, and smaller compared with other Rhizophora species; while its bark is either grey or dark grey, and sometimes longitudinally fissured.
Rhizophora mucronata. This member of the Rhizophoraceae family is commonly called loop-root mangrove, red mangrove, or Asiatic mangrove. Found on the coastal areas and river banks in the Indo-Pacific region, this specie is locally called rooiwortelboom in Afrikaans; isikhangathi in Xhosa, and; umhlume in Zulu languages, respectively.
The Rhizophora mucronata is characterized by an evergreen, medium to tall trees with several multi-branched, hoop or pile-like stilt roots looping from branches and stems. Its leaves are leathery, broadly elliptic to oblong-elliptic in shape with very dark black dots on the underside. Its bark is smooth and sometimes scaly brown or reddish.
Sonneratia caseolaris. Commonly known as Crabapple Mangrove, or Mangrove Apple, the Sonneratia caseolaris is a member of the Lythraceae plant family. You will easily recognized this specie, especially at night, because fireflies often congregate on it.
Its leaves are simple and shiny with a reddish-pink base; while its bark is grey and flaky with spongy outer surface. The external appearance of its fruit is like that of the persimmon fruit.
Xylocarpus rumphii. Belonging to the Meliaceae family, this specie bears the common name, Cedar mangrove. It is characterized by a small, evergreen tree with no prominent above-ground breathing root. It has compound leaves with ovate to cordate leaflets that are long and shiny. Its bark is brown, rough, and fissured.