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Coasts: Opportunities and Hazards » Coral Reefs: Importance, Threats and Protection

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 2.3.6

What coral is and where coral reefs are found around the world
Why coral reefs are important to people and wildlife
The main threats to coral reefs
Strategies and techniques that protect and manage reefs, and how to judge them

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What is a coral reef?

A coral reef is an underwater ridge or mound built over a very long time by tiny animals called coral. Reefs look like colourful rock gardens, but they are alive. They are some of the most valuable ecosystems on Earth.

Key terms:

Coral polyp: a tiny soft-bodied animal that builds a hard, stony skeleton around itself.
Coral reef: a structure made from the skeletons of millions of coral polyps, built up over thousands of years.
Algae: tiny plant-like living things. On a reef they live inside the polyps.
Biodiversity: the variety of living things in a place.
Coral bleaching: when stressed coral loses its algae and turns white.
Ocean acidification: the ocean becoming more acidic because it absorbs extra carbon dioxide from the air.
Marine protected area (MPA): a part of the sea where activities such as fishing are limited by law.

Coral polyps and algae live together and help each other. The algae make food from sunlight and share it with the polyps. The polyps give the algae a safe home. The algae also give coral its bright colours. This partnership is why reefs need sunlight.

Where are coral reefs found?

Coral needs very particular conditions, so reefs only grow in some places. Learn these four conditions: warm, shallow, clear and salty water.

🌞 Warm

Reefs grow in tropical seas, mostly between about 30 degrees north and 30 degrees south of the Equator. The water must stay warm, usually above about 18 degrees Celsius.

🌊 Shallow and clear

The algae need sunlight, so reefs grow in shallow, clear water. Muddy water blocks the light.

🧂 Salty

Coral needs normal sea water. Water that is less salty, for example near the mouth of a big river, is a problem for reefs.

📍 Why rivers matter

Rivers bring mud and fresh water, which cloud and freshen the sea. So reefs are usually missing where large rivers reach the sea.

Four reef regions you should be able to name:

The Caribbean: reefs around islands and the coast of Central America.
The Red Sea: reefs along the coasts of Egypt, Saudi Arabia and neighbouring countries.
The Coral Triangle: the seas around Indonesia, the Philippines and Papua New Guinea. It has more kinds of coral than anywhere else.
The Indian Ocean: reefs around tropical islands and along the coast of East Africa.

If you are asked to describe the distribution on a map, say that reefs form a band either side of the Equator, then name one or two regions.

Why are coral reefs important?

Reefs cover a tiny part of the sea floor, yet they matter a great deal. Sort the reasons into groups to help your exam answers:

Type	Importance
Environmental	Biodiversity: reefs are home and nursery to a huge number of fish and other sea life. Coastal protection: reefs break waves before they reach the shore, which reduces erosion and flooding.
Economic	Fishing: reef fish feed local people and are sold. Tourism: divers, snorkellers and beach visitors bring money and jobs to hotels, boat trips and shops.
Social	Food and ways of earning a living for coastal communities, especially in LICs. Medicines: some reef animals and plants are studied as sources of new medicines.

Because so many people and species depend on them, damage to a reef has effects at a local, national and global scale.

What threatens coral reefs?

Most of the serious threats today are linked to people. Learn them in two groups.

🌡 Global threats

Coral bleaching: warming seas stress the coral, so it pushes out its algae and turns white. The coral can recover if the water cools soon enough, but if the heat lasts it starves and dies.
Ocean acidification: more carbon dioxide dissolves in sea water and makes it more acidic. This makes it harder for coral to build its skeleton.

🏭 Local threats

Pollution: sewage, farm fertiliser and mud washed in from the land harm coral and cloud the water.
Overfishing: removes too many fish, which upsets the balance of the reef.
Blast fishing: using explosives to stun fish. It kills all sea life nearby and smashes the reef.
Tourism damage: boat anchors, divers touching coral and people walking on reefs break the coral.
Coastal development: building hotels and ports can bury coral in dust and mud, or destroy it directly.

Common mistakes

Do not say that coral bleaching is caused by pollution. The main cause is warmer sea water. Also, bleached coral is not always dead, but it is weak and at risk. Another mistake is to write only "pollution" without saying what the pollution is and how it harms the coral.

How can coral reefs be protected and managed?

A strategy is an overall plan or agreement. A technique is a method used to carry it out. For reefs, the aim is sustainable management: using the reef to meet today's needs without damaging it for future generations.

Technique	How it works	Strength	Weakness
Marine protected areas	Law limits fishing and other activities in the area.	Reef and fish stocks can recover.	Needs rangers and money to enforce. Local fishers may lose their income.
Fishing limits	Rules on how many fish, what size and which methods, including a ban on blast fishing.	Keeps fish stocks healthy for the future.	Hard to police over a wide sea area.
Mooring buoys	Boats tie to fixed buoys instead of dropping anchors onto coral.	Cheap and stops anchor damage.	Does nothing about warming or pollution.
Reducing runoff	Less fertiliser and sewage reach the sea, for example through treatment plants and planting trees and grass strips beside rivers.	Cleaner, clearer water.	Needs work across the whole area that drains to the sea, so it is slow and costly.
Coral gardening and restoration	Small coral fragments are grown in underwater nurseries, then fixed to damaged reef.	Brings back damaged areas and creates local jobs.	Slow and expensive, and new coral can still bleach if the sea stays too warm.
Ecotourism rules	Tourists are limited in number and given rules: no touching coral, no standing on reefs, no littering. Money from visitors can pay for protection.	The reef brings in money and stays healthy.	Hard to make sure that everyone follows the rules.

No single technique solves every problem. Local actions, such as mooring buoys, deal with local threats. Bleaching and acidification are global threats, so they can only be reduced if countries cut their carbon dioxide emissions. The most effective management combines local protection with action on climate change.

Judging a strategy

When asked to evaluate or assess, consider these questions for each technique:

How well does it deal with the threat?
How much does it cost, and can an LIC afford it?
Who benefits and who loses (fishers, tourists, local people)?
Is it sustainable, so the reef will still be there for the future?

Then give a clear judgement. For example, a marine protected area may be strong for fish stocks but weaker where there is little money for rangers.

Exam-style question

Fig. 1.1 is a table of made-up survey data for two reefs, Reef A and Reef B, in the same sea.

Feature	Reef A	Reef B
Live coral cover	70%	25%
Fish seen per dive	about 200	about 40
Fishing rules	Marine protected area	No rules
Boats using anchors	None (mooring buoys)	Many

(a) Identify two conditions needed for coral to grow. [2 marks]

(b) Describe two ways in which Reef B shows signs of damage compared with Reef A. [2 marks]

(d) To what extent can marine protected areas and mooring buoys keep reefs healthy? [6 marks]

Model answer

(a) Warm water (1) and shallow, clear water so that light reaches the algae (1). Salty water is also accepted.

(b) Reef B has far less live coral cover, 25% against 70% (1). It also has far fewer fish, about 40 per dive against about 200 (1).

(c) Warm sea water stresses the coral (1). The polyps push out the algae that live inside them (1). The coral turns white and loses its food source, so it can starve and die (1).

(d) Top level answer (5-6 marks): Marine protected areas and mooring buoys are strong local techniques. Reef A has an MPA and mooring buoys, with 70% live coral and about 200 fish per dive, compared with 25% and about 40 at Reef B, which has no rules and many anchors. The MPA limits fishing so fish stocks can recover, and mooring buoys stop anchors breaking the coral. Mooring buoys are cheap, and an MPA costs less than coral gardening, though it needs money for rangers. However, they only deal with local threats. They do nothing to stop warming seas, which cause bleaching, or ocean acidification. They also need money for rangers to enforce them, and local fishers may lose income. Overall, they can keep a reef healthy to a large extent against local damage, but they are not enough by themselves, because the global threats need action to cut carbon dioxide emissions as well.

Exam tip

In a six-mark "to what extent" question, use figures from Fig. 1.1, give strengths and weaknesses, and end with a judgement that answers the question.

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