2.3. Coral reefs

Question 1

What are coral polyps?

Answer 1

• tiny, soft animals whic attach themselves to a hard surface in shallow seas where there is sufficient light for growth (photosynthesis) => exude calcium carbonate as the grow which form skeletons
• polyps have small algae (zooxanthelllae) growing inside them
• there is a symbotic relationship between polyps and algae - algae get shelter and food from polyp, polyps grow as algae grows (get food via photosynthesis)

Question 2

Conditions for coral reefs to grow

Answer 2

• Temperature: between 23C to 25C
• Depth of water: less than 25cm but not exposed to air, below low tide mark
• Salinity: between 32psu and 42psu
• Light: shallow water because algae in coral reefs photosynthesise
• Sediment: minimal as it clogs up their feeding structures and reduces light available
• Wave action: strong wave action which ensures oxygenated water; removes any trapped sediment
• Global distribution: tropical seas between Tropics of Cancer and Capricorn

Question 3

What are the 4 forms of reef?

Answer 3

• Fringing reef
• Barrier reef
• Atoll
• Patch reef

Question 4

Characteristics of fringing reef

Answer 4

• Near coastline around islands and continents
• Characterised by an outer reef edge capped by an algal ridge
• A broad reef flat
• A sand floored boat channel close to the shore
• Grow sea ward from the land
• Grow around newly formed islands which subside, or sea levels rise relative to land

Question 5

Characteristics of barrier reef

Answer 5

• Commonly separated from the shore by a wide deep lagoon
• Following a rise in sea level or a drop in the level of the land
• At their shallowest point they can reach the water’s surface forming a barrier

Question 6

Characteristics of atoll

Answer 6

• Rings of coral that create protected lagoons
• Usually form when islands surrounded by fringing reefs sink into the sea OR the sea level rises
• When the island disappears beneath the sea => atoll is formed

Question 7

What are the 3 theories of coral reef formation?

Answer 7

• Darwin-Dana
• Murray
• Daly

Question 8

.Darwin-Dana

Answer 8

1. An oceanic volcano which emerges from the sea surface and froms an island, becomes colonised by reefs building corals
2. The growth of corals begins to form a fringing reef. The island begins to sink slowly. Coral growth continues
3. The island continues to sink and a barrier reef is formed with a lagoon between the reef and island. Coral growth is more vigorous
4. Eventually the island disappears below the sea surface, leaving an atoll consisting of a ring of small islands

• Evidence: submergence takes place in the case of drowned valleys along parts of Indonesia and along the Queensland Coast of Australia

Question 9

Murray

Answer 9

• Base of the reef consisted of a submarine hill
• Coral grows upon suitable stable submarine platforms with unchanging sea level
• If submarine platforms above sea level => subjected to wave erosion
• After getting a suitable depth of 180 feet, coral polyps start growing to form fringing reefs
• Continuous outward growing of polyps form barrier reefs
• Atolls are formed due to the outward growth of corals in all directions at the top of the submarine platform

Question 10

Daly

Answer 10

• Rise in sea level is responsible (evidence: rise took place in post glacial times as ice sheets melted due to warm conditions)
• Previous coral reefs provided a base for the upward growth

Question 11

Coral reef management

Answer 11

• Damaging fishing practices like dynamiting can be banned. It is important that this is enforced or the practices will carry on.
• Conservation zones where tourists aren’t allowed or there numbers are restricted can be created.
• Areas where coral reef cannot be farmed can be created
• Fish stocks can be enhanced and quotas imposed on amount being caught
• Sewage outlets can be moved downstream of coral reefs
• Banning the dropping of anchors on coral reef.
• Reduce the use of fertilisers near coral reefs
• Finally one of the most important is educating people about why coral reefs are important and how we can protect them.