Mangrove Swamps

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Mangrove

A mangrove swamp consists of any sort of tree or shrub that is classified under the families Acanthaceae, Arecaceae, Combretaceae, Lythraceae, and Rhizophoraceae. These partially submerged plants grow in dense forests in the shallow waters of muddy coasts, tidal estuaries, and salt marshes.

A mangrove swamp consists of any sort of tree or shrub that is classified under the families Acanthaceae, Arecaceae, Combretaceae, Lythraceae, and Rhizophoraceae. These partially submerged plants grow in dense forests in the shallow waters of muddy coasts, tidal estuaries, and salt marshes. Mangroves are well-known for having exposed roots – called prop roots – that extend above the water level and support the rest of the plant. Many species in mangrove swamps also have respiratory or ‘knee’ roots called pneumatophores. These structures stay above the muddy floor and allow air to pass through small openings called lenticels. 

Mangroves usually grow to 9 metres in height. Their leaves grow on short stems, are opposite, oval-shaped or elliptic with smooth edges, are thick with surfaces akin to leather, and range from 5–15 centimetres long. The flowers of mangroves are pale yellow in colour. The common mangrove’s fruit is sweet and nutritious. Some mangrove species yield strong and hardy bark. A water-soluble tanning substance can also be obtained from a mangrove’s astringent bark. 

However, different mangrove species have characteristics distinct from the typical mangrove. Take the black mangrove as an example. This species typically grows to the moderate height of a large shrub or small tree. At times, black mangroves can reach heights of 18–21 metres. The black mangrove’s leaves are 5–7.5 centimetres in length, opposite, either oblong or akin to the tip of a spear shape, with a glossy green upper surface and a pale lower surface that appears white or grey in colour. Its flowers are small, white, slight, yet are often visited by honeybees for their strong fragrance and large amounts of nectar. 

Mangroves propagate through their fruit in a very special way. At the beginning of this process, the mangrove fruit remains attached to its parent branch. A long embryonic root quickly grows downward after emerging from its seed. This young root, called a mangrove propagule, falls in the right position for it to grow in the mud. The propagule grows long enough to be rooted in the mud before the fruit is completely separated from the parent tree. 

Mangrove Swamps

Mangroves thrive in clusters called mangrove swamps or mangrove forests found in the tropical and subtropical areas of the world. The plants that call mangrove swamps home are halophytic or salt-loving and can survive in water with high salt content. Mangrove swamps are found in the brackish waters of estuaries, where freshwater from rivers meets and mixes with the saltwater in the ocean. In this environment, the water is always a mix of saltwater and freshwater, but the concentration of salt changes with the tides every day. Over millennia, mangroves have developed distinctive adaptations to survive in these unique conditions, which allow them to live in salty environments while minimising the risk of moisture loss and preventing the plant from drying out. One such adaptation is apparent in the leaves. These contain specialised glands that secrete the salt that the mangrove absorbs. The leaves are also covered in a waxy coating called a cuticle that helps the plant retain water. 

Flora

Mangrove swamps have little diversity in terms of plant species. These environments are dominated by mangrove variants which can be classified into three: black mangrove, red mangrove, and white mangrove. 

White Mangroves (Laguncularia racemosa) are considerably less unique than the other two variants. This species grows out of the water in areas further inland. Their location does not necessitate special adaptations such as arching roots (prop roots), and roots that protrude from the water (pneumatophores).

In inland swamps, the Black Mangrove (Avicennia sp.) is the most abundant species. Characteristic of this type, Black Mangroves have roots called pneumatophores that protrude from the water and are exposed to the air above. The exchange of gases is poorly facilitated in underwater soil, and the roots of this species have adapted to absorb gas directly from the air above the water. 

On the coast, the most common type of mangrove is the Red Mangrove (Rhizophora mangle). When thinking of mangroves, the image of the Red Mangrove is likely to be the first to come to mind. Red Mangroves have unique, arching prop roots that keep the body of the plant above water level. The prop roots of the Red Mangrove originate from its trunk, growing downwards into the water, branching out over and over again to form a dense web of roots. 

Red Mangroves play an essential role in coastal habitats. Their roots trap sand and hinder coastal erosion, and lay down a strong foundation for other plants to grow. Some examples include buttonwood, ferns, pines, sea grape, and mangroves of other varieties. The roots of Red Mangroves also provide shelter to a plethora of animal species. During storms, mangroves protect the coast by acting as a buffer against storm surges and tidal waves. 

Fauna

Mangrove swamps are important habitats for a variety of animal species. Above the water, they are home to birds, reptiles, and even mammals. Birds such as herons, mangrove cuckoos, brown pelicans, cormorants, frigatebirds, snowy egrets, white ibis, eagles, and red-tailed hawks fly above the vegetation and rest in the mangroves’ branches. Lizards, such as anoles,  cling to the mangrove trunks and branches, while other reptiles like turtles, sea turtles, alligators, and crocodiles swim in the water below. Monkeys and manatees make up the few mammals that live in these semi-aquatic environments. 

 Aquatic organisms and sea creatures account for a great majority of animals that live in these ecosystems. Countless species of fish thrive in the tangle of mangrove roots growing underwater. Among these are jacks, snappers, gar, mullet, tarpon, bonefish, moles, and sheepshead. Other organisms such as crustaceans, molluscs, and invertebrates also exist in great numbers. Mangrove tree crabs, spotted mangrove crabs, snails, mussels, barnacles, oysters, sponges, and anemones all shelter under the protection of mangrove roots. Thick foliage and abundant organic material make mangrove roots ideal nurseries for species of larval shrimp and crabs. Invertebrates such as bacteria, protozoa, and worms are also critical components of the mangrove ecosystem. Bacteria are particularly essential for the decomposition of dead organic matter and for replenishing nutrients in the ecosystem. 

The Importance of Mangroves 

Mangroves play many important roles in the intertidal zones and coastlines where they reside. The mangrove forest or mangrove swamp creates unique wetland ecosystems that become home to a large diverse collection of living organisms. Mangroves also have significant effects on the abiotic factors of natural environments. They are cheap and effective ways to mitigate disaster risk along coastlines. Mangroves protect coastlines from erosion, as well as the effects of storms, strong waves, and flooding. 

Climate

Through their capture of carbon from the atmosphere, mangroves make a significant contribution to the regulation of our planet’s climate. Trees and plants in terrestrial forests store the majority of their carbon in their trunks and branches. Terrestrial forests are also prone to losing stored carbon through fire. On the other hand, mangroves in mangrove swamps and forests store most of their carbon in their root systems and the soil in which they are anchored. In this way, mangrove forests are able to become carbon sinks that store carbon in the earth for extended periods. Fires are much less likely to break out in mangrove forests, allowing these plants to retain their carbon for longer. 

Benefits to Coastal Ecosystems

To maintain the ecological balance of coastal ecosystems, mangroves work in harmony with the seagrass beds and coral reefs. Mangrove roots trap sediment and pollutants and prevent them from being washed out into the ocean. Seagrass acts as a barrier that protects coral reefs from silt and mud that can smother them. Consequently, coral reefs protect both seagrass and mangroves by acting as a buffer against strong ocean waves that rush onto the shoreline. 

Nursery Grounds

Many animal species find safety and shelter in mangrove forests. Mangroves also become safe places for the offspring of many marine species. The dense network of partially submerged roots are nurseries for many young marine species until they are large enough to move into coral reefs, or venture out into the ocean. The branches of mangrove trees provide ideal nesting places and migratory sites for various avian species. 

Mangroves are breeding grounds for many marine animals such as fish, crabs, shrimp, and other shellfish. During their juvenile stages, fish species such as tarpon, snook, and barracuda initially take shelter in the maze of mangrove roots. When they have grown sufficiently, they venture out into seagrass beds. Finally, in adulthood, they swim out to the open ocean. It is estimated that three-quarters of fish caught commercially originated in mangrove roots, or are otherwise connected to mangrove forests through the food web. 

Habitat

Thousands of species live and thrive in mangrove forests. These species come from all levels of the forest and marine food web, ranging from the apex predator Bengal tiger, to the barnacle and unnoticeable bacteria. The dense foliage is a shelter for many insect species. For many varieties of shorebirds and migratory birds, they are perfect sites for both nesting and resting. Some bird species found in mangroves include egrets, herons, and kingfishers. Larger animals such as monitor lizards, fishing cats, and crab-eating macaques hunt for smaller creatures in the mangrove forest. In the soft soil where mangroves take root, snails and clams bury themselves and bide their time. Crustaceans such as crabs and shrimp scour the nutrient-rich mud for food. Mangroves swamps are also habitats for endangered species including dugongs, tree-climbing fish, proboscis monkeys, ridley turtles, and white-breasted sea eagles. 

Food and nutrients

Leaves that fall from mangrove trees contribute a significant amount of nutrients to their ecosystem. Dead and decayed mangrove leaves decompose and their nutrients are distributed among algae and invertebrates. In turn, small organisms such as young fishes, shrimp, jellyfish, worms, anemones, sponges and birds then feast on these organisms. As they are carried by the tides, the nutrients from decomposed mangrove matter make their way to estuaries, mudflats, and coral reefs, providing food for organisms that lie on the seabed. 

Clean Water

In a way, mangroves act as stewards of the waters that they grow in. Through their intricate root systems, mangroves filter nitrates and phosphates from rivers and streams. Mangrove forests also hinder saltwater from invading freshwater waterways found inland. 

Natural Resources

Human communities also benefit from mangroves. Mangroves provide coastal communities with a livelihood through fishing and ecotourism and as an important source of food such as fish and shellfish. Mangroves are undoubtedly a critical part of the food security of the human communities that benefit from them. 

However, the welfare of many mangrove ecosystems is in danger because of human activity. In the last 50 years, half of the world’s mangrove cover has been lost to being cut for firewood, coastal development, and being cleared away for shrimp farms. Mangroves are also directly threatened by pollution from inland sources. Untreated sewage waste, disposed plastics, and by-products from agricultural sources pose significant threats to mangrove ecosystems. 

References 

Action Group on Mangrove Ecosystems and Livelihoods. (n.d.). Retrieved from The Commonwealth Blue Charter: https://bluecharter.thecommonwealth.org/action-groups/mangrove-restoration/

mangrove. (n.d.). Retrieved from Britannica: https://www.britannica.com/plant/mangrove

Mangrove Swamps. (n.d.). Retrieved from United States Environmental Protection Agency: epa.gov/wetlands/mangrove-swamps

Mangrove Swamp. (n.d.). Retrieved from Exploring Nature:https://www.exploringnature.org/db/view/Mangrove-Swamp

Why Mangroves Matter. (n.d.). Retrieved from American Museum of Natural History: https://www.amnh.org/explore/videos/biodiversity/mangroves-the-roots-of-the-sea/why-mangroves-matter

Cite/Link to This Article

  • "Mangrove Swamps". Geography Revision. Accessed on July 5, 2022. https://geography-revision.co.uk/gcse/physical-gcse/mangrove-swamps/.

  • "Mangrove Swamps". Geography Revision, https://geography-revision.co.uk/gcse/physical-gcse/mangrove-swamps/. Accessed 5 July, 2022.

  • Mangrove Swamps. Geography Revision. Retrieved from https://geography-revision.co.uk/gcse/physical-gcse/mangrove-swamps/.