The big idea: Coral reefs and mangrove swamps are two of the most valuable coastal ecosystems. Both grow in warm, shallow, tropical water and both protect the coast, store carbon and support huge biodiversity.
They are also among the most threatened environments on Earth. Option B tests how they form, why they matter (their value to people and nature) and the natural and human threats that are destroying them.
Key terms for this micro
- Coral reef - a ridge built by tiny coral polyps that need warm, clear, shallow, sunlit water.
- Coral bleaching - corals expel the algae that feed them when the water gets too warm, turning white and often dying.
- Ocean acidification - extra CO2 dissolves in seawater, making it harder for corals to build their skeletons.
- Mangrove swamp - salt-tolerant trees rooted in the sheltered intertidal zone of tropical coasts.
- Ecosystem services - the benefits an ecosystem gives people (coastal protection, fisheries, tourism, carbon storage).
- Stakeholder - any group with an interest in the ecosystem (fishers, tourists, residents, governments, conservationists).
Where each one grows: Coral reefs need clear, warm, shallow, salty water with plenty of sunlight - so they grow on open tropical coasts away from muddy rivers.
Mangroves need sheltered, low-energy, shallow tropical water - so they grow in estuaries, lagoons and behind reefs, where the reef calms the waves for them.
How this is tested: Paper 1 Option B opens with a data-response on a map or graph of an ocean ecosystem. You Identify the region with the highest value, Estimate a percentage off the graph (units not required) or read a land-use share off a map. Always read the correct row and quote the value carefully.
| Ocean region | Reefs destroyed (%) |
|---|---|
| Indian Ocean | 34 |
| South-East Asia / Pacific | 28 |
| Caribbean and Atlantic | 22 |
| Red Sea and Gulf | 16 |
| Eastern Pacific | 11 |
Identify = read the extreme; Estimate = read a value: Identify the region usually means the highest (or lowest) value - find the biggest number and name its region. Estimate means read one value off the figure to a sensible tolerance. Always name the region, not just the number.
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Both ecosystems give ecosystem services - real benefits to nature and to people. Examiners want the service AND its development: name the benefit, then explain how it works or who gains from it. A value tied to a stakeholder scores the development mark.
| Service | Coral reefs | Mangrove swamps |
|---|---|---|
| Coastal protection | Break wave energy before it reaches the shore, reducing erosion | Tangled roots absorb storm-surge and trap sediment, shielding villages |
| Fisheries | Breeding and nursery grounds for reef fish - income for fishers | Nursery for prawns, crabs and juvenile fish - vital for local catches |
| Tourism / economy | Diving and snorkelling jobs, hotels, dive operators | Eco-tourism, boardwalk visitors, crab and honey harvesting |
| Carbon and water | Reef framework stores carbon; clear water sustains life | Store large amounts of 'blue carbon'; filter run-off and pollution |
Real ecosystems - the value in numbers: The Great Barrier Reef (Australia) supports tens of thousands of tourism jobs and shelters the Queensland coast from cyclone waves.
The Sundarbans (Bangladesh and India) is the world's largest mangrove forest - its roots blunt cyclone storm-surges that would otherwise drown low-lying delta villages, and its waters are a key prawn and fish nursery.
Name the stakeholder: An Explain the value answer scores its development marks by linking each benefit to who gains - residents, fishers, tour operators, governments. Mangroves protect the coast is the reason; so delta villagers avoid flooding is the development.
Natural and human threats: Reefs and mangroves face natural threats (warming seas, acidification, storms, disease) and human threats (overfishing, pollution, coastal development, tourism, clearing mangroves for aquaculture).
The biggest driver is climate change: warmer water causes coral bleaching and extra CO2 causes ocean acidification, which weakens coral skeletons. Local human pressures then push damaged reefs and mangroves over the edge.
Human threats and their mechanism
- Overfishing / dynamite fishing - strips the reef of fish and shatters the coral framework.
- Pollution and run-off - sediment and nutrients cloud the water and smother coral; farm chemicals poison it.
- Coastal development and tourism - dredging, anchors and careless divers break fragile coral.
- Mangrove clearance - cutting mangroves for shrimp ponds (aquaculture) and building removes the whole habitat.
Real threats and a real response: Across the Indian Ocean, repeated marine heatwaves have bleached large stretches of reef since 2000. In South-East Asia, vast areas of mangrove have been cleared for shrimp aquaculture.
The Galapagos Marine Reserve (Ecuador) shows the response: a large protected zone that limits fishing and tourism so the ecosystem can recover - evidence that managing the human threats can work even while the natural ones (warming) continue.
How this is tested - the [10] Examine essay: Paper 1 Option B ends with a 10-mark Examine essay, marked on markbands. The recurring version weighs the natural and human threats to coral reefs and their relative seriousness.
Top band needs: accurate terms, two or more developed threats (natural and human), named examples or data, a weighing of their relative scale / how it changes over time, and a clear conclusion.