Coral Reefs

You should be able to…

• Describe the conditions required for the development of coral reefs

• Understand the global distribution of coral reefs that results from this

• Describe fringing and barrier reefs and atolls

• Appreciate that coral reefs are under threat from human activity

Coral Reef Formation• The polyp forms the basis

of life on the coral reef.• It builds reefs through the

production of a calcium carbonate skeleton which it constructs as it grows.

• Polyp growth is the result of a symbiotic relationship between the polyp and zooxanthellae (algae) which rely on photosynthesis for their growth.

• The zooxanthellae provide essential nutrients to the polyp to enable growth.

Conditions required

• Temperature: 23-25°C; • Water Depth: less than 25m but not

exposed to air; • Light: for photosynthesis; • Salinity required; • Clean, clear water, sediment free, • Well oxygenated water produced by

strong wave action;

Global Distribution

Global distribution: Tropical seas between Tropics of Cancer and Capricorn. Offshore, on eastern and western continental and island margins. 92% of total found in Indo-Pacific region.

Type of Reef• Fringing reef – reef that is directly

attached to a shore or borders it with an intervening shallow channel or lagoon.

• Barrier reef – reef separated from a mainland or island shore by a deep lagoon; see Great Barrier Reef.

• Atoll reef – a more or less circular or continuous barrier reef extending all the way around a lagoon without a central island; see atoll.

From Wikipedia

Reef Theories

• Charles Darwin postulated that fringing reef, barrier reef and atoll development happened through geological time as a result of continued reef growth and volcanic subsidence.

• James Dwight Dana (a geologist) provided evidence top support Darwin's theory of uplift and subsidence.

After Darwin

Dana’s Evidence

Reginald Daly (20th Century)

• An island emerges from the surface of the sea.• Sea levels drop significantly during an Ice Age.• Horizontal terraces and ledges are cut by

erosion during the period of low sea level.• As the Ice Age ends the sea level rises.• Coral reef growth subsequently takes place on

the newly created submerged platforms.

Daly in Diagrams

The 3D Theory of Coral Development

The modern explanation of coral reef development should correctly be called the

Darwin/Dana/Daly Theory (The 3D Theory!) of Coral Reef Formation since only the works of

these three men taken together can fully explain the characteristics observed on atolls today.

Threats to Coral Reefs

The Impacts

Coral Bleaching

Damaged Coral

Coral Reef Management

• What can be done to protect the worlds coral reefs?

• Why is protecting coral reefs important?

Case Study

• Great Barrier Reef (Australia)

Marine Park Website