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Coasts: Opportunities and Hazards » Mangroves: Importance, Threats and Protection

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 2.3.6

What mangroves are and where in the world they grow
How mangrove trees cope with salt water and mud
Why mangroves are so important to people and wildlife
The threats to mangroves and how they can be protected and managed

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What are mangroves?

Mangroves are trees and shrubs that grow along the shore, with their roots in salty or brackish water. Brackish water is a mix of fresh water and sea water, found where a river meets the sea. Together the trees make a thick forest that is flooded and drained by the tide twice a day.

Key terms:

Mangrove: a tree or shrub that can grow in salty, waterlogged coastal mud.
Estuary: the wide mouth of a river where fresh water meets the sea.
Nursery: a safe place where young animals, such as baby fish, grow up before moving elsewhere.
Carbon store: a place that takes carbon dioxide out of the air and keeps it locked away.
Sustainable use: using mangroves in a way that meets people's needs today without destroying them for the future.

Where are mangroves found?

Mangroves need warmth, so they grow on tropical and subtropical coasts, in a band either side of the Equator. They also need calm water. Strong waves would tear up young trees, so mangroves grow on sheltered coasts, in estuaries, lagoons and behind islands, where soft mud builds up.

The Sundarbans: a huge mangrove forest where the Ganges and Brahmaputra rivers reach the Bay of Bengal, shared by Bangladesh and India.
Indonesia: thousands of islands with sheltered, muddy coasts, and one of the largest areas of mangrove of any country.
Brazil: mangroves along much of its warm Atlantic coast and around the mouth of the Amazon.
West Africa: mangroves in river deltas and estuaries, for example in Nigeria and Guinea-Bissau.

To describe the distribution on a map, say that mangroves form a band in the tropics and subtropics, then name two or three regions.

How do mangroves cope with salt water?

Most trees die in salt water and in mud with little oxygen. Mangroves have special features that let them survive:

🌿 Roots above the mud

Many mangroves have stilt-like roots that stick up out of the mud. These roots let the tree take in air and hold it steady in soft ground.

🍃 Dealing with salt

Some mangroves filter out salt at the roots. Others push salt out through their leaves, so you may see white crystals on them.

Why are mangroves important?

Type	Importance
Environmental	Coastal protection: the dense roots slow waves and storm surges and trap mud, so the shore is eroded less. Nursery for fish: young fish, crabs and prawns shelter among the roots. Carbon store: mangroves and their muddy soil hold large amounts of carbon, which helps to slow climate change. Biodiversity: birds, monkeys, reptiles and many other species live there.
Economic	Fishing: the fish and crabs that start life in mangroves support local catches. Wood: used for building and fuel. Tourism: boat trips and wildlife watching.
Social	Livelihoods and food for coastal communities, many of them in LICs. Safety: fewer homes and lives lost in storms.

Remember that mangroves also act as a natural barrier against tropical storms, as you saw in the lesson on managing tropical storms.

What threatens mangroves?

🦐 Clearance for farming and building

Mangroves are cut down to make ponds for shrimp farms, and cleared for hotels, ports, roads and housing. This is a major threat in many places.

🪓 Logging

Trees are cut for timber, fuel wood and charcoal. If they are cut faster than they regrow, the forest shrinks.

🛢 Pollution

Oil spills, sewage, farm chemicals and plastic waste coat the roots and poison the mud and the animals that live there.

🌊 Sea level rise

If the sea rises faster than mud can build up, trees are drowned. If buildings or sea walls sit behind them, the mangroves have no space to move inland.

When mangroves are lost, the coast is less protected, fish catches fall and stored carbon is released into the air. People in nearby communities then lose both food and income.

How can mangroves be protected and managed?

The aim is to protect what is left and to restore what has been lost. Sustainable management means local people can still earn a living from the mangroves without using them up.

Strategy or technique	How it works	Strength	Weakness
Replanting	Seedlings are planted on bare or cleared coast.	Restores protection and fish nurseries	Many seedlings die if the wrong species or site is chosen, and a new forest takes years to mature
Protected areas	Law bans clearing in a national park or reserve.	Stops the worst damage	Needs rangers and money to enforce
Community management	Local people look after the forest and agree rules for its use.	Locals benefit, so they want it to last	Needs training and support, and poverty can still push people to cut trees
Sustainable harvesting	Only a limited amount of wood, fish and crabs is taken, and trees are left to regrow.	Provides income and keeps the forest	Hard to check that limits are kept
Laws	Rules that ban or limit clearing for shrimp ponds and building, with fines.	Covers a whole country	Weak if laws are not enforced

The best results usually come from combining techniques, for example a protected area run by the local community, with replanting where damage has happened.

Common mistakes

Saying mangroves grow on any coast. They need warm, sheltered water and soft mud, so they are found in the tropics and subtropics, not on exposed coasts.
Saying mangroves "stop" storms. They reduce the energy of waves and surges, they do not remove the risk.
Writing "they are important" with no reason. Always say why: protection, fish nursery, carbon store, livelihoods or biodiversity.
Listing techniques without judging them. Give a strength and a weakness for each one.

Exam-style question

Fig. 1.1 is a photograph of a mangrove forest in a sheltered estuary. In the background a small area has been cleared for shrimp ponds.

(a) Identify two features of the coast shown in Fig. 1.1 that suggest mangroves are growing there. [2 marks]

(b) Explain why mangroves are important for coastal communities. [4 marks]

Model answer

(a) Any two: the water is sheltered and calm (1); the coast is a muddy estuary or lagoon (1); the setting is tropical or warm (1). [2 marks]

(b) Mangrove roots slow waves and storm surges, so homes and farmland are protected from flooding and erosion (1). Young fish and crabs shelter and grow among the roots, so local fishers have a food supply and income (1). People can use the wood for building and fuel (1). Tourists pay for boat trips and wildlife watching, which brings jobs (1). [4 marks]

(c) This is a Level 3 answer (5-6 marks): it gives balanced strengths and weaknesses, uses detail, and reaches a clear judgement. A Level 2 answer (3-4 marks) would give mostly one side with some detail, and a Level 1 answer (1-2 marks) would only make simple points. Community management has strengths because local people depend on the forest, so they have a reason to look after it and follow rules they agreed themselves. It is cheaper than paying outside rangers. It lets people take limited wood and fish, so they still earn a living. However, it also has weaknesses. Communities may need training and money to manage it well. Poverty may still push some people to cut trees or sell land for shrimp farms. Outsiders may ignore local rules unless the law backs them up. Overall, it works best when combined with laws and protected areas, so it is a good approach but not the only one. [6 marks]

Exam tip

For an "Assess" question, give strengths and weaknesses of the one approach, then finish with a clear judgement. Do not just list the good points.

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