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Coral Restoration

2020 JAN 27

Preliminary   > Environment and Ecology   >   Biodiversity   >   Coral bleaching


The Zoological Survey of India (ZSI), with help from Gujarat’s forest department, is attempting for the first time a process to restore coral reefs using biorock or mineral accretion technology. A biorock structure was installed one nautical mile off the Mithapur coast in the Gulf of Kachchh.


  • Biorock is the name given to the substance formed by electro accumulation of minerals dissolved in seawater on steel structures that are lowered onto the sea bed and are connected to a power source, in this case solar panels that float on the surface.
  • When a positively charged anode and negatively charged cathode are placed on the sea floor, with an electric current flowing between them, calcium ions combine with carbonate ions and adhere to the structure (cathode). This results in calcium carbonate formation. Coral larvae adhere to the CaCO3 and grow quickly.
  • The fragments of broken corals are tied to the biorock structure, where they are able to grow at least four to six times faster than their actual growth as they need not spend their energy in building their own calcium carbonate skeletons.
  • The location for installing the biorock had been chosen keeping in mind the high tidal amplitude in the Gulf of Kachchh. The low tide depth where the biorock has been installed is four metres, and at high tide it is about eight metres.
  • India has four coral reef areas, Andaman and Nicobar Islands, Lakshadweep, Gulf of Mannar and the Gulf of Kachchh.
  • The ongoing initiative of coral restoration using biorock technology could potentially help to sustain the earlier successes. The technology helps corals, including the highly sensitive branching corals, to counter the threats posed by global warming.


  • Coral are made up of genetically identical organisms called polyps. These polyps have microscopic algae called zooxanthellae living within their tissues.
  • The corals and algae have a mutualistic relationship.
  • The coral provides the zooxanthellae with the compounds necessary for photosynthesis.
  • In return, the zooxanthellae supply the coral with organic products of photosynthesis, like carbohydrates, which are utilized by the coral polyps for synthesis of their calcium carbonate skeletons.
  • In addition to providing corals with essential nutrients, zooxanthellae are responsible for the unique and beautiful colors of corals.
  • They are also called the “rainforests of the seas”.
  • There are 2 types of corals:
  • Stony, shallow-water corals—the kind that build reefs.
  • Soft corals and deep water corals that live in dark cold waters.


  • When corals face stress by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae zooxanthellae living in their tissues, causing them to turn completely white. This phenomenon is called coral bleaching.
  • The pale white colour is of the translucent tissues of calcium carbonate which are visible due to the loss of pigment producing zooxanthellae.
  • Corals can recover if the stress-caused bleaching is not severe.
  • Coral bleaching has occurred in the Caribbean, Indian, and Pacific oceans on a regular basis.
  • Causes of Coral Bleaching
  • Rise in Sea Temperature: Most coral species live in waters close to the warmest temperature they can tolerate i.e., a slight increase in ocean temperature can harm corals. El Nino elevates the sea temperature and destroys coral reefs.
  • Ocean Acidification: Due to rise in carbon dioxide levels, oceans absorb more carbon dioxide. This increases the acidity of ocean water and inhibits the corals ability to create calcareous skeletons, which is essential for their survival.
  • Solar radiation and ultraviolet radiation: Changes in tropical weather patterns result in less cloud cover and more radiations which induce coral bleaching.
  • Infectious Diseases: Penetration of bacterium like vibrio shiloi inhibits photosynthesis of zooxanthellae. These bacteria become more potent with elevated sea temperatures.
  • Chemical Pollution: Increased nutrient concentrations affect corals by promoting phytoplankton growth, which in turn supports increased numbers of organisms that compete with coral for space.
  • Increased Sedimentation: Land clearing and coastal construction result in high rates of erosion and a higher density of suspended silt particles which can
  1. smother corals when particles settle out (sedimentation),
  2. reducing light availability (turbidity) and
  3. potentially reducing coral photosynthesis and growth.
  • Human Induced Threats: Over-fishing, pollution from agricultural and industrial runoff, coral mining, development of industrial areas near coral ecosystems also adversely impact corals.

Prelims Question

Q. Consider the following statements regarding Coral Reefs:
1.The corals and algae have a mutualistic relationship.
2. Zooxanthellae are responsible for the unique and beautiful colors of corals.
3.The recent initiative of coral restoration using biorock technology helps corals, including the highly sensitive branching corals, to counter the threats posed by global warming.
Which of the statements given above is/are correct?
a)1 only
b)2 and 3
c)1 and 3
d)All of the above

Answer to the Prelims Question