8.3 Coral Reefs

Question 1

Distribution of Coral Reefs

Answer 1

Mostly between Oceania and South East Asia.
Mostly between the Tropics.
North Australia and Indonesia.

Question 2

Fringing Reefs

Answer 2

Low, narrow bands of coral next to the coast.
The surface is slightly concave and filled by a shallow lagoon between the land and the outward edge of the reef.
Seaward edge is often highest due to breaking waves oxygenating water providing food for polyps.

Question 3

Barrier reefs

Answer 3

Similar to fringing reefs but several km from the land.
The land is separated from coral by a wide deep lagoon.
The floor of the lagoon is made of coral suggesting they used to be fringing reefs.

Question 4

Atoll reefs

Answer 4

A type of coral reef that forms when a volcanic island sinks beneath the sea, leaving a ring of coral around a lagoon.

Question 5

Development of atoll reefs (Darwin theory)

Answer 5

By subsidence, Fringing reefs are succeeded by barrier reefs and then by atoll reefs.
As an island subsides, the corals continue to grow keeping pace with subsidence.
Coral growth is more vigorous on the outer side of the reef creating a higher rim, the inner parts form a wide and deep lagoon.
The inner island is submerged forming a ring of coral that is the atoll.

Question 6

Development of atoll reefs (stand still Murray)

Answer 6

The subsidence of submarine platforms.
Submarine platforms could be erosion or built up by deposition until it was a suitable height for corals to grow.

Question 7

Development of atoll reefs (Daly’s glacial theory)

Answer 7

The ice age caused a lowering of the sea level by 125-150m.
When the ice age ended, temperatures started rising, and corals started growing over the platforms, which were lowered due to marine erosion.

Question 8

Conditions required for coral growth

Answer 8

Temperature (between 23-25 degrees)
Depth (majority of reefs withing 25m but can grow up to 30m)
light (shallow water as 98% of nutrition from photosynthetic algae)