Conditions for the Survival of Coral Reefs

What are Corals and Coral Reefs?

  • Coral or coral polyps are lime secreting small marine invertebrates. Their dead bodies result in built up of coral reefs.
  • They live in large colonies.
  • When these corals die, their skeleton accumulate on one site.
  • The continued accumulation and compaction of these skeletons leads to the formation of coral reefs and atolls.
  • These reefs become home to a lot of sea organisms such as fish, urchins, crabs, shrimps etc.
  • GK: These coral reefs are more diverse than the tropical rainforests and have 1 million species of organisms. Hence, they are also called rainforests of the ocean.

Conditions for the Survival of Coral Reefs

Following conditions are necessary for survival of coral reefs.

  1. Warm waters: The corals are mainly found in tropical waters because they need 20°-21°C mean annual temperature of water to survive but they can survive in 23°-29°C too. Toot high or too low temperature of water is fatal for coral polyps which leads to bleaching of coral reefs.
  2. Shallow waters: Coral polyps thrive in shallow waters i.e. between 200 and 250 feet of depth. This is so because they need sunlight and oxygen for survival. The deep water are deficient of sunlight and oxygen. The deep sea water is deficient in calcium carbonate or lime. So, if coral reefs are exposed to lime deficient water, they will dilute in the sea water quickly.
  3. Clean and Sediment-free Water: Sediments clog coral mouth. So, they can not intake food or oxygen properly leading to ultimate death. This is why, the coral reefs are not located near the mouths of the large sediment-laden rivers.
  4. Fresh Water is Injurious: The fresh water is more acidic than sea water. It also changes the salinity of seas water. The presence of fresh water lead to increase in acidity and decline in salinity leading to erosion of coral reefs.
  5. Corals need Calcium as food and Habitat: The water with very high salinity and very low calcium is deadly to corals. The highly saline water and low calcium water will dilute the coral reefs. Hence, the corals are not found in areas of too high or too low salinity. Such areas are deficient in calcium.
  6. Currents and Waves: The currents and waves are favorable to corals as they supply fresh food (planktons) to polyps.
  7. Extensive Submarine Platform: An extensive submarine shallow platform, of about 250 feet depth, is ideal for the growth of coral polyps’ colony.

What is Coral Bleaching?

Corals live in symbiosis with algae. Corals provide the algae with a safe platform and compounds for photosynthesis. In return, the algae provide corals with oxygen and also removes waste products from reefs. When the conditions around polyps’ colonies are not suitable, they expel the algae and the corals turn white. This even is called coral bleaching. The coral bleaching puts the corals in stress. The corals may survive short period of bleaching. If the underlying cause of bleaching continues to prevail, the corals start to die. El Nino has led  to many coral bleaching events in the past.