8.3. Coral Reefs

Question 1

Coral Reefs

Answer 1

• Tiny marine animals called polyps that form reefs when millions of them live together in colonies
• Their skeletons are cups of calcium carbonate which join together to form a hard, stony mass of limestone
• As one generation of corals die, the next one grows on top of it, so the reef grows upwards and outwards compete for food
• Reef has to have a base to grow on
• Once established coral reefs can grow up to 60cm a year if the conditions are right

Question 2

Relationship between Coral Polyps and Photosynthesising Algae

Answer 2

• Coral polyps are like tiny animals that live in a symbiotic relationship with algae called zooxanthellae.
• The algae live inside the bodies of the coral polyps and use CO2 and water that the polyps produce in respiration to carry out photosynthesis, which produces sugar and oxygen.
• The coral polyps then use these to grow and respire. There is recycling of products

Question 3

Coral Bleaching

Answer 3

• When environmental conditions become stressful for the photosynthetic algae, they leave the coral polyps, which lose their colour and eventually due to lack of food.
• The coral reefs turn white as this happens, and is known as coral bleaching

Question 4

Conditions required for coral growth

Answer 4

1) Temperatures - above 18 degrees celsius, but grow best between 22-25 degrees celsius
2) Cannot grow in water deeper than 30m, because the algae need light to photosynthesise. The best is shallow waters up to 10m deep
3) Outer edge of reef grows highest because there is where oxygen and food supplies are most abundant - in the zone where waters break
4) Corals grow best where salt levels are high - prefers seawater with salinity levels between 32 and 42 psu
5) Coral polyps cannot survive for long above water, so most of the reef is at or below the tide level
6) Polyps need clean, clear, sunlit water so they can’t live where rivers bring muddy sediments into the sea
7) There has to be a solid surface on which the reef can grow This is why they are coastal features, forming on shallow offshore waters

Question 5

Types of coral reef

Answer 5

1) Fringing Reefs
2) Barrier Reefs
3) Atolls

Question 6

Fringing reef

Answer 6

• Low, narrow bands of coral next to the coast, at about low tide level
• Consist of a platform of coral which is connected to the land and which has grown out from it
• Usually has a concave surface and is filled with a shallow lagoon (less than 500m wide)
• Seaward edge of the reef is often the highest part because this is where the breaking waves oxygenate the water and make food available for the polyps
• Corals grow in shallow waters where it is found today
• Examples: Coral coast of Fiji

Question 7

Barrier reef

Answer 7

• Similar to structure to fringing reefs but are usually several kilometers from the land and are always over 0.5km from the shore
• The reefs are separated from the land by wide, deep lagoons which are too deep for the polyps to live
• Despite this, the floor of the lagoon is usually made of old coral which indicates that these barrier reefs may have originated as fringing reefs which slowly grew out from the coastline
• The seaward edge of the reef is often the highest part anad the outer edges of the reef slope steeply down into the sea beyond
• Corals which grow in shallow waters, but grow outwards from the coastline to form barrier reefs, where the island is slowly sinking
• Example: The Great Barrier Reef

Question 8

Atoll

Answer 8

• Coral is broken from the reef by the waves is deposited inside the reef where it forms the floor of the lagoon
• Narrow, circular reefs, broken by channels
• They surround a deep, circular lagoon
• No clear connection to any island or landmass
• The island of the barrier reef continues to subside and so coral forms the floor of the lagoon
• Examples: Suvadiva Atoll and Gan Atoll in the Maldives

Question 9

Why are coral reefs important?

Answer 9

1) Environmental Reasons (diversity, coastal protection)
2) Economic reasons (food, tourism, products)
3) Medical Reasons

Question 10

Environmental Reasons for why coral reefs are important

Answer 10

Diversity

• Extremely diverse ecosystems - there are over 800 types of coral and the reefs provide a habitat for a wide range of other creatures
• Corals provide a habitat for over 25% of all known species - “rainforests of the sea”

Protection

• Coral reefs protect the coastline from storm waves and can even break the power of tsunami waves
• Also protect the coastline from erosion, coastal flooding and can shelter ships in ports and harbours

Question 11

Economic reasons for why coral reefs are important

Answer 11

Seafood

• Coral reefs can yield up to 15 tons of fish and other seafood per km squared
• It is believed that they provide food for up to a billion people in Asia alone

Commercial products

• Corals and shells can be made into jewelry while live coral and fish are harvested and sold for use in aquariums
• Sand and limestone can be mined for use in the building industry
• However, this is unsustainable as it leads to be very destructive of the reef ecosystem

Tourism

• Many tourists visit the coral reefs to marvel at the colours and wildlife of the reef
• Snorkeling and scuba diving
• Rapidly growing industry that can provide much needed income in LICs

Question 12

Medical reasons for why coral reefs are important

Answer 12

Some of the organisms in the reef may produce chemicals that can be used to cure disease, potentially skin cancer and some viral diseases

Question 13

Threats to coral reefs

Answer 13

1) Enhanced Global Warming
2) Pollution
3) Physical Damage

Question 14

Enhanced Global Warming as a threat to coral reefs

Answer 14

• Main threat is climate change
• If temperatures increase by only 1 or 2 degrees celsius coral bleaching can be the result. Increase in temperature may be temporary, but effects can be permanent
• Global warming leads to rising sea levels and if the sea rises faster than the coral can grow; the reefs will be drowned in deep water
• Global warming is increasing the acidity of ocean waters. More carbon dioxide in the atmosphere means that more of it dissolves in the oceans. This leads to a rise in the acidity of the oceans, which in turn stresses the coral polyps by making it more difficult to build and maintain their limestone shells

Question 15

Pollution as a threat to coral reefs

Answer 15

• Land-based pollution - economic growth in may LICs means that industrial and agricultural pollutants are more likely to get into the rivers which then bring pollutants to the sea
• Chemicals in agricultural has encouraged the growth of phytoplankton which in turn feed increased numbers of the Crown of Thorns starfish which swarm onto the reefs and eat the coral
• Shipping - oil pollution, plastic waste can smother and kill the coral
• Raw sewage from growing coastal settlements and sewage from tourist resorts pollute waters which encourage growth of phytoplankton

Question 16

Physical Damage as a threat to coral reefs

Answer 16

Overfishing leads to a reduction in biodiversity of the coral reefs as there is less natural breeding
- Modern fishing methods use nets and other equipments that physically damage the coral reefs
- Tourism - walking on the reef, collecting coral and shells, swimmers stirring up sediment from the sea bed
Sediment from ship propellers, draining from the sea lead to the deaf of a reef. Polyps need clean, clear, sunlit water
- Natural hazards - tropical areas are susceptible to tropical storms. The large waves and storm surges associated with these storms can do severe damage to coral reefs

Question 17

Why is it hard for governments (especially LICs) to protect the world’s remaining coral reefs?

Answer 17

• Many countries where coral grows are LICs where the government has other priorities and money is in short supply
• It is difficult to enforce laws to protect the reefs

Question 18

Main strategies to protect coral reefs

Answer 18

1) Combating global warming by reducing emissions of carbon dioxide and other greenhouse gases. This should ameliorate the increase of global sea temperatures which is the main cause of coral bleaching. Will also slow down the increase in acidity of the ocean waters
2) Reducing local threats such as trampling, mining, overfishing, sedimentation and coral blasting
3) Helping LICs to introduce legislation and providing funds so that the new laws can be enforced
4) Providing locals with jobs that do not damage the coral
5) Designating coral reefs as nature reserves, especially the ones that have not experience too much damage

Question 19

Fiji

Answer 19

• A group of tropical islands in the South Pacific Sea
• All islands are surrounded by coral reefs, two-thirds of which are thought to be at risk
• Fiji’s coral coast is fringed with the world’s second largest reef
• In the past 20 years there has been an enormous effort to conserve coral reefs in fiji

Question 20

Environmental Importance of Fiji’s coral reefs

Answer 20

• The reefs are very rich ecosystems with great biodiversity
• Fiji’s 300 species of coral are home to almost 2000 species of fish, including sharks, tuna, many shellfish and endangered turtle species
• The reef ecosystem hs links to other bigger ecosystems through the food chain
• Fiji’s reefs are also important to storm waves and reducing the impact on land
• The plants and animals in the reef ecosystem are also being researched as possible future sources of medicines

Question 21

Economic Importance of Fiji’s coral reefs

Answer 21

• Both subsistence and commercial farming provide good livings
• Colourful reefs and marine life attract tourists, especially as Fiji is a stopover point for people who want to break up the long flight across the Pacific Ocean

Question 22

Why are reef conservation methods needed in Fiji?

- Human Reasons

Answer 22

• Corals are extremely sensitive organisms that can die if touched
• Despite measures by locals, the coral have been affected by overfishing, as well as by boat and anchor damage
• Fiji was one of the world’s largest exporters of coral and coral fish for aquariums
• Tourists walking on the coral and snorkeling and diving among the reefs have also caused damage
• Rapid population growth → Development of settlements has led to harmful sediment, sewage and other pollutants being washed out in the reefs

Question 23

Why are reef conservation methods needed in Fiji?

- Environmental Reasons

Answer 23

• Every 3 or 4 years, Fiji is battered by cyclones which generate destructive waves that break the coral
• These storms also lead to large amounts of nitrates and phosphates reaching the reefs from run-off from agricultural land, which causes the number of Crown of
• Thorns starfish (which feed on the polyps) to increase
• Every so often, the rise of sea temperature causes the bleaching of the reefs, because it leads to the death of the colourful algae that lives within the polyps and leaves the bleached white coral behind. In time, the polyps, deprived of food, also die

Question 24

Efforts by locals to conserve the reef

Answer 24

• In Fiji, the reefs are also of cultural importance and the local people hold ceremonies to thank them.
• They have been long aware of the importance of the reefs and have traditionally regulated their use.
• The people have banned fishing in certain areas when stocks have been threatened by overfishing

Question 25

Efforts by a Fijian resort to conserve the reef

Answer 25

• Many hotels and communities in Fiji are trying to conserve the coral reefs on which their livelihoods depend
• The Hide-away Resort is an example. The resort uses World Ecotourism, award-winning coral reef conservation programme of integrated coastal management
• The resort fronts directly onto the fringing reef and makes visitors aware of its great importance. The area has been made into a protected zone.
• Guests can snorkel on the high tide, but putting feet down onto the coral is not allowed
• Guided walks are organised along a specifically provided reef path
• At high tide, guests can view the marine life on the reef from the resort’s glass-bottomed boat
• In the lagoon there is a coral nursery where coral is planted and protected
• Notices in the garden remind visitors of the importance of the reef