2.3. Coral reefs Flashcards Preview

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Flashcards in 2.3. Coral reefs Deck (11)
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What are coral polyps?

  • 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)


Conditions for coral reefs to grow

  • 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


What are the 4 forms of reef?

  • Fringing reef
  • Barrier reef
  • Atoll
  • Patch reef


Characteristics of fringing reef

  • 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


Characteristics of barrier reef

  • 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


Characteristics of atoll

  • 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


What are the 3 theories of coral reef formation?

  • Darwin-Dana
  • Murray
  • Daly



  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



  • 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



  • 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


Coral reef management

  • 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.