MANGROVES: CHARACTERISTICS, TYPES, FLORA, CLIMATE, FAUNA, EXAMPLES - BIOLOGY - 2025

The mangroves are ecosystems of trees and shrubs adapted to live in the intertidal zone of tropical and subtropical coastal seas. The name of this ecosystem comes from its characteristic trees, which the Guaraní Indians called mangle ("twisted tree").

The mangrove area on the planet is estimated at 20 million hectares, both on the continental coast and on the islands. Although in the course of the last 100 years between 35 and 50% of mangrove ecosystems have been lost, particularly in India, the Philippines and Vietnam.

Mangrove swamp in Cambodia. Source: Leon petrosyan

The mangrove includes a mixture of land, the sea and fresh water contributions from rivers, so there are variations within the same mangrove as well as between mangroves. It has been determined that the greater the fresh water contributions, the greater the mangrove development.

The mangroves show a marked zoning of species in a gradient defined by the level of flooding, salinity and amount of oxygen available in the substrate. So some species grow only along the shoreline, others further inland, and so on.

This ecosystem has a simple vertical structure, consisting of an upper layer of trees and a sparse undergrowth of herbs and shrubs. However, in the horizontal dimension there is a variation in the floristic composition.

Mangrove species have developed highly specialized adaptations to survive in these conditions. Among others are the roots specialized for breathing (pneumorrhizae with pneumatophores) and glands that excrete accumulated salt.

The mangrove is one of the most productive biomes, serving as a feeding, reproduction and refuge area for numerous aquatic species and birds. This biome is subdivided into two large types that are the western mangroves and the eastern mangroves.

In addition, they have delimited 49 mangrove ecoregions, 40 of them in the western region and 9 in the eastern one.

From 54 to 60 mangrove species are recognized, belonging to 20 genera and 16 families of angiosperms. The most widespread plant family is Rhizophoraceae and in particular the species Rhizophora mangle.

Mangroves develop in tropical and subtropical climates, with variable rainfall and temperatures according to the region. The precipitations can go from 100-150 mm annually to 3,500 mm; with temperatures of 23 to 48 ºC.

In these ecosystems there is a great diversity of both terrestrial and aquatic fauna. There are numerous species of fish, crustaceans and bivalves; as well as aquatic mammals such as the manatee.

There are also different species of crocodiles and turtles; while on land there are numerous species of insects, reptiles, birds and mammals. Among the mammals are from the tiger to the elephant, through deer, tapirs and primates.

Various economic activities are carried out in the mangrove areas, such as timber extraction, hunting and fishing. Agriculture, livestock, aquaculture, beekeeping and tourism are also developed.

A representative example of mangrove ecoregions of the eastern group is the Sundarbans mangrove (Bay of Bengal, India-Bangladesh). This is the largest mangrove ecoregion on the planet, formed in the delta generated by the Ganges, Brahmaputra and Meghna rivers.

Here the main mangrove species is the sundri (Heritiera fomes), a mallow whose wood is highly valued.

Another prominent example, in this case from the western group, is the mangrove swamps of the Orinoco Delta (Venezuela), Guyana, Suriname and French Guiana. The largest mangrove ecoregion in America, formed by the deltas of the Orinoco rivers to the west, San Juan to the center and Oiapoque to the east.

The characteristic species of mangroves in this area are those of the genus Rhizophora: Rhizophora mangle, Rhizophora racemosa and Rhizophora harrisoni.

General characteristics

- Plant structure

The plant formation known as mangrove swamp has a poorly developed vertically structure. Generally there is a single layer of trees, whose height varies from 7 to 40 m, depending on the species and the region.

The specific composition of this tree stratum varies from the coastline inland and from region to region. Mangroves with high tidal variations and large freshwater inputs are more extensive and with taller trees.

Understory

There is an understory that varies from the coastline inland. In the coastal strip of the mangrove formed by the species that live directly in the sea, there is no understory.

However, as we move away from the coast, a lower layer of herbs and shrubs appears. At first this understory is very sparse and scattered and later it acquires greater density.

Epiphytism and climber

The tropical mangroves have some climbing plants and epiphytes, although they do not reach the levels of the tropical forest. Bromeliads occur as epiphytes (plants that live on other plants) in the mangroves along the Caribbean Sea.

- Floor

The substrate where the mangrove develops varies in a transept drawn from the coast inland. The species adapted to grow on the coastline, dip their roots in seawater and anchor themselves to the bottom.

This ocean floor is a combination of sand and silt, in an environment of high salinity and low oxygen concentration. As we move away from the coast, the species vary, adapting to a less saline and more oxygenated substrate.

However, most of them are flooded soils or soils with a high water table, and a high content of salts. This is due to the fact that they are soils subject to the effect of daily tides and their seasonal variations.

Histosols

According to the classification of the Reference Soil Group, the most common type of soil in the mangrove is Histosol. These are peaty, saline soils, with reducing characteristics due to being subjected to periodic marine flooding.

Additionally, being tidal is added as a qualifier (it is flooded with tidal water, but it is not covered by water at mid low tide). Likewise, the term sapric is incorporated into the characterization, referring to its content of decomposed organic matter.

- Physiography

Mangroves develop in coastal areas with little exposure to sea waves. For example in gulfs, deltas, inlets, estuaries, coasts protected by island barriers or corals.

About 60-75% of the coastline of the Earth's tropical regions is lined with mangroves.

- Ecology

Mangrove System- Marine Grassland- Coral Reef

Despite their low floristic diversity, mangroves play an important role in the energy flows of coastal systems. In addition, they provide a large amount of organic matter that is partly retained by the submerged roots that stabilize the fine sediments.

On the other hand, they form a buffer zone for the waves with shallow areas and regulate salinity due to fresh water inputs. All this allows the development of underwater pasture meadows, with species such as Thalassia testudinum.

In these meadows, young of various fish and other organisms from the nearby coral reefs breed and feed.

Marine nursery

The mangrove ecology constitutes a suitable zone for the reproduction, refuge and feeding of diverse marine species. Many species of coral reef fish come to the mangrove to reproduce and breed and for this they are called "marine nurseries".

The tides

The exchange generated by the tides between the sea and the land in the mangroves is vital. The tides allow the mobilization of nutrients, the dispersal of seedlings and inhibit the establishment of competing species.

Additionally, the ebb and flow of seawater reduce salinity in areas of high evaporation. This is because when the water evaporates from the ground the salt concentrates, but the current of the tidal water carries it back to the sea.

Salinity

The concentration of salts in water and soil is a determining factor in the ecology of the mangrove. Salinity varies both between mangroves in different regions, and in a mangrove from the coast to the interior.

A determining factor in salinity is the fresh water input that the mangrove receives. In some cases, mangroves develop at the mouths of large rivers and there the concentration of salts decreases.

For example in the Orinoco River delta in Venezuela, the Niger River delta in Nigeria or the Mekong River in Vietnam. This allows the mangroves to reach a greater development in extension and height.

The concentration of salts also varies with the season and in the delta of the Niger River in the rainy season the concentration of salts is 0 to 0.5%. Later, when the dry season enters and the river flow decreases, the saline concentration rises to 30-35%.

Available oxygen

Another fundamental factor is the concentration of available oxygen, taking into account that it is a partly aquatic ecosystem. In other words, the ecosystem ranges from a liquid medium, through flooded soil, to soil with a high water table (brackish underground water).

Advance of the coastline

The dynamics of the mangrove allows the formation of new coastal land, helping to expand the mainland. This is achieved thanks to the network of roots that fixes the contributions of sediments that arrive.

- Adaptations

Mangroves are made up of highly specialized tree species in their adaptations to the marine environment. This includes morphological and physiological adaptations to survive in a soft, salty, low-oxygen soil environment.

Pneumorrhizae and pneumatophores

One of the modifications that mangroves have to survive in the oxygen-scarce environment are pneumorrhizae. These are roots with negative geotropism, that is, unlike typical roots, they grow upwards.

These roots protrude vertically from the ground and have pore-like structures called pneumatophores. Pneumatophores fulfill the function of gas exchange, that is, they allow the radical system to receive aeration.

These adaptations occur in mangrove species that grow in seawater or on coastal marshy soils. For example, in the black mangrove (Avicennia germinans) and the white mangrove (Laguncularia racemosa).

Stilt roots

There are species such as Rhizophora mangle that grow in the intertidal zone (between the maximum and minimum levels of the tides). In this area, the substrate is very soft and unstable so these plants develop numerous arched aerial roots.

Mangrove in Puerto Rico. Source: Boricuaeddie

These roots allow the plant to hold on to the substrate and at the same time form a network in which sediments are deposited. In this way, a firmer substrate is consolidated.

On the other hand, stilt roots also develop pneumatophores and therefore facilitate gas exchange.

Salt-secreting glands

Another highly specialized adaptation of mangroves is the salt-secreting glands. These anatomical structures expel the salt that penetrates the plant through the absorbed seawater to the outside.

It is an active expulsion of water drops loaded with salt, which are then dried in the wind. Later the rain or the wind itself drag the salt deposited on the leaves.

Viviparity

Another adaptation of some mangrove species, such as Rhizophora, is viviparity (the seeds germinate in the fruit while it is still on the tree). Subsequently the seedling falls and is transported by the water until it reaches a suitable point to anchor and grow.

This gives the seedlings a better chance of survival, since it would be very difficult for them to germinate while floating in seawater.

- Anthropic impact

Mangroves worldwide have been subjected to strong human pressure. These ecosystems are deforested to clear the coast for various purposes.

Among others, tourist infrastructures, aquaculture, industries or to facilitate access to the sea are established.

Other activities that also affect mangroves by altering their hydrography are the construction of dikes or roads. Likewise, the application of herbicides and oil spills and derivatives affect mangroves.

Types

The types of mangroves existing in the world are defined by the two recognized centers of diversity for this biome. They are the western group located in the Atlantic region and the eastern group located in the Indo-Pacific region.

In addition, the Global Network 200 of the World Wildlife Fund (WWF) identifies up to 49 mangrove ecoregions.

The Western Group

It covers the entire tropical coast of the Caribbean and the Gulf of Mexico (continental and insular) and in this group the WWF delimited 40 of its mangrove bioregions. Also, the American Pacific coast from the north of Peru, Ecuador, Colombia, all of Central America to Baja California (Mexico).

It continues to spread along the Atlantic coast of the northeast and east of South America to southern Brazil. On the Atlantic coast of Africa it stretches from Senegal, through the Gulf of Guinea, to the northwestern coast of Angola.

The Eastern Group

It stretches along the eastern coast of Africa from Mozambique, Tanzania, and Kenya to southern Somalia. Likewise, mangroves develop on the western coast of Madagascar.

There are scattered areas in the Red Sea and the Gulf of Oman, and along the Asian and Indian coasts in the Indian Ocean. Later it covers almost all the continental and insular coasts of Southeast Asia and Oceania, from the Indian Ocean to the Pacific.

The largest extension of mangroves in this region occurs in the Malay Archipelago. In the eastern group the WWF has described 9 mangrove bioregions.

Flora

The species that define the mangrove have very particular characteristics that are given by their adaptation to salinity and oxygen deficiency in the substrate. In this sense, 54 to 60 mangrove species are recognized, belonging to 20 genera and 16 families of angiosperms.

Additionally, 20 species of 11 genera and 10 families have been identified as minor components of the mangrove.

Main families

Rhizophoraceae is the most widespread geographically with the genera Rhizophora (eight species), Bruguiera (6 species), Ceriops (two species) and Kandelia (one species). The genus with the widest distribution are the so-called red mangroves (Rhizophora).

Rhizophora mangle. Source: Samuel Thomas

Other families of importance are Avicenniaceae with the genus Avicennia (eight species) and Lythraceae with the genus Sonneratia (five species). Followed by Combretaceae with the genera Laguncularia (one species), Conocarpus (one species) and Lumnitzera (two species) in addition to the Arecaceae (Nypa) family.

The underwater meadows

Associated with the mangrove are the underwater meadows of submerged aquatic angiosperm species. These include the Thalassia testudinum meadows in tropical America.

Western mangroves

The mangrove genera and species present in the western group are Rhizophora with R. mangle, R. racemosa and R. harrisonii. Additionally Avicennia (Avicennia germinans), Laguncularia (L. racemosa) and Conocarpus (C. erectus).

Eastern Mangroves

In the eastern mangroves there is a greater diversity, with more than 40 species. Of the Rhizophoraceae family are the genera Rhizophora (7 species), Bruguiera (6 species), Ceriops (3 species) and Kandelia (1 species).

In the Sundarbans mangroves (India-Bangladesh-India) the dominant species is Heritiera fomes of the Malvaceae family. The eastern mangroves are the habitat of Nypa fruticans a palm, Aegiceras corniculatum (Primulaceae) and Sonneratia species (Lythraceae).

Weather

The climate in the mangrove is tropical to subtropical with specific geographic variations, especially in precipitation. In most cases the mangrove regions are subject to a dry season and a rainy season.

Precipitation

Precipitation is highly variable in the geography of the mangrove biome worldwide. For example, they are low in the semi-arid coast of the Caribbean (100 to 150 mm) and high in the deltas of the great rivers (1,700-3,500 mm).

Temperature

The coastal areas receive high levels of solar radiation, so the temperatures are relatively high (23-37 ºC). For example, on the coast of the Caribbean Sea the average annual temperature is around 26 ºC.

For its part, in the Mekong River delta the annual temperature during the day ranges from 30 to 34 ºC, while at night it drops to 23-26 ºC. In the Sundarbans mangroves (India-Bangladesh-India) temperatures can reach 48 ºC.

Fauna

Mangrove fauna is much more diverse than flora and consists of a particular combination of terrestrial and aquatic species. Terrestrial species range from insects to monkeys and cats as well as various species of birds.

Other species such as crabs live between the sea and the land and sea turtles come to lay their eggs on the beaches.

In the aquatic environment, the species of fish, molluscs and bivalves that inhabit the mangrove are very diverse. There are also mammals such as the manatee and the pygmy hippopotamus.

West africa

Manatee (Trichechus senegalensis) and pygmy hippopotamus (Choeropsis liberiensis) inhabit the mangroves of the west coast of Africa. Also turtles like the softshell turtle (Trionyx triunguis).

Pygmy hippopotamus (Choeropsis liberiensis). Source: Chuckupd

The Nile crocodile (Crocodylus niloticus) is also located, which despite its name, inhabits all of Africa. Primates include the Sclater's ginger (Cercopithecus sclateri) and the southern talapoin (Miopithecus talapoin).

America

In the American mangroves there is a species of manatee (Trichechus manatus) and various species of monkeys, such as the capuchin monkey (Cebu apella). Also, reptiles such as the green iguana (Iguana iguana), the coastal caiman (Crocodylus acutus) and the spectacled caiman (Caiman crocodilus).

Manatee (Trichechus manatu). Source: Reid, Jim P, US Fish and Wildlife Service

It is also the habitat of different species of sea turtles, such as the hawksbill turtle (Eretmochelys imbricata) and the green turtle (Chelonia mydas).

Southeast Asian

There are several species of deer such as the sambar (Rusa unicolor), the hog deer (Axis porcinus), the mouse deer (Tragulus javanicus). Also the only species of tapir outside of America, the Malayan tapir (Tapirus indicus, endangered).

Likewise, the wild boar (Sus scrofa) inhabits these forests and the Asian elephant (Elephas maximus) in the dry season comes down to feed in the mangrove and drink salt water.

The marine crocodile (Crocodylus porosus) is found at various points along the coasts of India, Southeast Asia and Australia.

Economic activities

Mangroves are highly productive ecosystems that have traditionally been exploited by local communities. They also fulfill relevant environmental services that affect different economic activities.

Firewood

Mangrove wood has traditionally been used locally as firewood and for the production of charcoal. In the delta formed by the Ganges and the Brahmaputra, mangrove wood is harvested and sold as firewood.

Fishing and gathering

Mangrove areas, especially the deltas of large rivers, are home to large fish populations, providing abundant fish. On the other hand, the collection of various bivalves and crustaceans is also common.

Among these species are the oyster (Crassostrea spp.) And the crab or blue crab (Callinectes sapidus).

Aquaculture

Especially the establishment of farms for shrimp production. In this sense, it has been pointed out that this is the main cause of mangrove deforestation in Indonesia.

Agriculture and Livestock

Although the mangrove soils are not very favorable for agriculture, some items are established in them. For example, rice fields in Indonesia and pastures in Tumilco (Mexico) for livestock.

Beekeeping

In the Gulf of Mexico, Bangladesh and Australia mangrove honey production is a growing activity. For example, in the state of Veracruz and in Tabasco (Mexico) many small beekeeping companies have been established.

According to beekeepers, the black mangrove (Avicennia germinans) is the best supplier of nectar. The honey it produces is very liquid and tends to crystallize due to its high glucose content, it has a floral aroma and a sweet taste with a slight salty touch.

tourism

In various mangrove areas, national parks and reserves have been established, where the main activity is tourism. For example, the Morrocoy National Park on the western coast of Venezuela.

Industrial uses

Some useful components for the industry are extracted from the mangrove, such as tannins for tanneries. Mangroves have also been deforested to establish salinas (areas for the extraction of sea salt); for example in the delta of the Niger River.

Examples of mangroves in the world

- Sundarbans mangrove (Bay of Bengal, India-Bangladesh)

This is the largest mangrove ecosystem on the planet, occupying more than 18,000 km2. It is formed by the largest delta in the world, constituted by the confluence of the Ganges, Brahmaputra and Meghna rivers. The mangrove swamps across southern Bangladesh and the West Bengal state of India.

Sundarbans mangrove. Source: Thennavan Jayaraman

It is a region subject to monsoon storms from June to September, with annual rainfall of up to 3,500 mm. Daytime temperatures in these months can exceed 48ºC.

Vegetable species

The dominant mangrove species is the sundri (Heritiera fomes) a mallow whose wood is highly valued. Additionally there are several species of Avicennia, and two species of Xylocarpus (X. mekongensis and X. granatum).

As well as Sonneratia apetala, Bruguiera gymnorrhiza, Cereops decandra, Aegiceras corniculatum, Rhizophora mucronata and the Nypa fruticans palm.

Animal species

It is the only mangrove ecoregion where the largest carnivore in the Indo-Pacific, the tiger (Panthera tigris), lives. Among the tiger's prey are the chital deer (Axis axis), the barking deer (Muntiacus muntjak) and the wild pig (Sus scrofa).

It is also inhabited by some primates such as the Rhesus macaque (Macaca mulatta). There are 170 species of birds, including the brown-winged kingfisher (Pelargopsis amauropterus), which is endemic.

Among reptiles, two species of crocodiles stand out (Crocodylus porosus and C. palustris) and a gharial (Gavialis gangeticus). There is also a water monitor lizard (Varanus salvator) that reaches up to 3 m in length.

Activities

The land areas near the Bay of Bengal are arid, so natural resources are scarce. For this reason, the mangroves in the area have been a traditional source of various resources, such as wood, animal protein, tannins, salt and others.

Mangrove honey is also produced and fishing and agriculture (especially rice) are practiced.

- Mangroves of the Orinoco Delta (Venezuela), Guyana, Suriname and French Guiana

It comprises an extensive mangrove ecoregion of about 14,000 km2 with trees up to 40 m high. This ecoregion includes the Orinoco River delta (Venezuela), the San Juan River delta and the Oiapoque River delta (French Guiana).

It corresponds to a coastal strip of 0 to 4 ms. nm facing the Atlantic Ocean. Precipitation ranges from 960 mm in the extreme west to more than 3,000 mm in the east and the average temperature ranges from 25.4 ° C to 27.2 ° C.

Vegetable species

The species present are Rhizophora mangle, Rhizophora racemosa, Rhizophora harrisonii, Avicennia germinans and Laguncularia racemosa.

Additionally, herbs such as heliconia (Heliconia spp.), Costus arabicus, Cyperus giganteus and Eichornia crassipes are presented. Palms such as the chaguaramo (Roystonea regia) and the moriche (Mauritia flexuosa).

Some trees such as the blood dragon (Pterocarpus officinalis) indicate the transit to the freshwater swamp forest.

Animal species

There are about 118 species of birds, including more than 70 aquatic species, with populations of up to 5 million individuals. One of them is the scarlet ibis or red corocora, endemic to South America (Eudocimus ruber).

More than 50 species of mammals also inhabit this area, such as the howler monkey (Alouatta seniculus) and the Guiana saki (Pithecia pithecia). Also, carnivores such as the jaguar (Panthera onca) and the ocelot (Leopardus pardalis).

Sea turtles, including the endangered olive ridley turtle (Lepidochelys olivacea) nest on sandy beaches. Other reptiles are the slime (Caiman crocodilus) and the anaconda (Eunectes murinus).

Activities

Fishing, hunting, agriculture, breeding and gathering are the activities of the indigenous people of the area. One of the ethnic groups that inhabit the Orinoco delta are the Warao, who build palafitos (huts on the water) in the pipes.

Large-scale fishing is a very productive activity. The volume of catches in the mangrove area of ​​the Orinoco River represents approximately half of the total volume of fishing on the coast.

References

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7. World Wild Life (Viewed 4 Sep 2019). Taken from: worldwildlife.org