Topic– Part of static series under the heading – “Coral reef and marine ecosystem”
6) Explain the factors that impact the formation of coral reefs? Also, distinguish between fringing reef, barrier reef and atoll?(250 words)
Key demand of the question
The question expects to bring out the various factors such as temperature, salinity etc that are conducive to the formation of coral reefs. Next, we need to explain the difference between various types of coral reefs ie fringing reef, barrier reef and atoll.
Structure of the answer
Introduction – Explain that coral reefs are considered to be the tropical forests of marine ecosystem. Coral reefs are built by and made up of thousands of tiny animals coral polyps.
- Explain the factors that lead to the formation of coral reefs – sunlight; clean, clear and warm ocean water, temperature generally between 20-42 degrees C; depth of water; salinity requirement of 27-40 ppm; adequate food supply to nourish the polyps etc
- Draw a diagrammatic representation of fringing reef, barrier reef and atoll.
- Fringing reef – Fringing reefs are reefs that grow directly from a shore. They are located very close to land, and often form a shallow lagoon between the beach and the main body of the reef.A fringing reef runs as a narrow belt [1-2 km wide]. This type of reef grows from the deep sea bottom with the seaward side sloping steeply into the deep sea. Coral polyps do not extend outwards because of sudden and large increase in depth.The fringing reef is by far the most common of the three major types of coral reefs, with numerous examples in all major regions of coral reef development.
- Barrier reef – Barrier reefs are extensive linear reef complexes that parallel a shore, and are separated from it by lagoon. Mention that it is largest in size of the three. Barrier reefs are far less common than fringing reefs or atolls, although examples can be found in the tropical Atlantic as well as the Pacific.
- Atoll – An atoll is a roughly circular (annular) oceanic reef system surrounding a large (and often deep) central lagoon.
The lagoon has a depth 80-150 metres and may be joined with sea water through a number of channels cutting across the reef. Atolls are located at great distances from deep see platforms, where the submarine features may help in formation of atolls, such as a submerged island or a volcanic cone which may reach a level suitable for coral growth.