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Coral reefs and their formation | Zoology Optional Notes for UPSC PDF Download

Coral Reef Definition

  • Coral reefs are elevated biogenic structures in tropical seas, primarily composed of calcium carbonate, constructed predominantly by reef organisms.

Biome Characteristics of Coral Reef:

  • Coral reef biome is a distinct subdivision of terrestrial or aquatic ecosystems.
  • It encompasses the entire plant and animal life assembly and their interactions within the life layer.
  • The coral reef biome includes reef-building corals, diverse organisms, and their ecological interactions.

Reef Building Corals and Other Organisms


(A) Madreporarian (Stony) Corals:

  • Imperforate corals: Astraea, Flabellum, Favia, etc.
  • Perforate corals: Porites, Madrepora, Montipora, Acropora, etc.
(B) Other Corals:
  • Milliporans, Tubipora, Heliopora, alcyonarians like Fungia, gorgonarians.
(C) Non-coral Animals:
  • Mollusks, Foraminifera, sponges, sea anemones, various marine life like shrimps, crabs, lobsters, octopuses, etc.
  • Reef fishes including sharks, eels, and rays.
(D) Plants:
  • Calcareous coralline seaweeds such as Lithophyllum, Lithothamnion, and Melobasia.
  • Various algae like Ulva, Sargassum, Turbinaria, Gelidiella, Gracillaria, etc.
  • Sea grasses like Halophilia, Thalassia, Cymodocea, Enhalus, etc.

Conditions for Coral Reef Formation

  • Temperature: Ideal growth temperature between 20°C to 30°C, with the range of 25°C—29°C being most favorable.
  • Depth of the Sea: Typically grows in shallow water; optimum depth is related to sunlight penetration for photosynthesis.
  • Sunlight: Essential for photosynthesis of zooxanthellae in coral polyps; required for the growth of reef-building corals.
  • Clear Water: Water must be clear to permit sunlight penetration, crucial for photosynthesis.
  • Suspended Particles and Sedimentation: Clear water is necessary; sedimentation can inhibit coral growth.
  • Salinity: Tolerates salinities between 30 and 40 ppt.
  • Nutrient: Thrives in nutrient-poor areas; excess nutrients can smother corals.
  • Precipitation of Calcium: Necessary for the formation of coral skeletons.

Fossil Corals and Reefs of the Geologic Past:

  • Over 6,000 fossil coral species recorded in different oceans.
  • Tabulate corals and rugose corals formed reefs during the Palaeozoic era, replaced by Madreporarian corals during the Coenozoic era.
  • Fossils found in temperate and polar regions.

Types of Coral Reefs


(1) Fringing Reef or Shore Reef:

  • Extends directly from the shore into the sea; surrounds tropical islands or continental coastlines.
  • Comprises reef front, reef crest, and back reef areas.
  • Examples: Gulf of Mannar, Palk Bay, Andaman, Nicobar Islands.

Coral reefs and their formation | Zoology Optional Notes for UPSC

(2) Barrier Reef:

  • Resembles fringing reef but grows in deeper water.
  • Separated from the land by a lagoon.
  • Notable example: Great Barrier Reef off Australia.

Coral reefs and their formation | Zoology Optional Notes for UPSC

(3) Atoll:

  • Circular or horse-shoe shaped reef enclosing a central lagoon.
  • Usually forms around submerged volcanic islands.
  • Example: Lakshadweep Islands.

Coral reefs and their formation | Zoology Optional Notes for UPSC

Additional Types:

  • Table reefs, patch reefs, apron reefs, and bank reefs.

Theories Regarding Coral Reef Formation


(1) Darwin-Dana Subsidence Theory:

  • Fringing reefs transform into barrier reefs and then atolls due to land subsidence.
  • Supported by observations during Darwin's voyage.

(2) Semper-Murray Solution Theory:

  • Corals grow on high ocean peaks; deposition of sediments and solution lead to barrier reefs and atolls.
  • Controversial but still favored by some researchers.

(3) Submerged Bank Theory:

  • Coral reefs form on flat surfaces that submerge slowly, advocating independent origins for different reef types.

(4) Daly Glacial-Control Theory:

  • Suggests coral growth during glacial periods; rising ocean levels support reef formation.
  • Supported by calculations on the age of existing coral reefs.

Distribution of Coral Reefs


(A) Geographic:

  • Primarily found in tropical and subtropical Western Atlantic and Indo-Pacific oceans.
  • Regions include the Caribbean Sea, Red Sea, East Coast of Africa, Indian Ocean islands, and Pacific Islands.

(B) Bathymetric:

  • Limited vertical distribution due to declining sea temperature with depth.
  • Occupies less than one-tenth of one percent of the world ocean.

9. Role of Symbionts in Coral Reefs:

  • Coral polyps harbor symbiotic brown algae (zooxanthellae) in their gastrodermis.
  • Symbiotic relation involves mutual benefits, including sugar and oxygen production through photosynthesis.

10. Genera of Reef Building Corals in India:

  • C.S. Gopinath Pillai recorded 71 genera, including 199 species from various Indian regions.
  • Notable locations include Gulf of Kachchh, Palk Bay, Gulf of Mannar, Lakshadweep, Andaman, and Nicobar Islands.

Factors contributing to the destruction of coral reefs

  1. Excessive Siltation: Industrial discharges, waste disposal, and runoff carrying pollutants lead to the death of reefs.
  2. Salinity Changes: Large volumes of freshwater from rivers reduce salinity, threatening coral reefs.
  3. Tropical Storms: Severe storms and hurricanes cause widespread coral mortality.
  4. Exploitation for Commercial Purposes: Removal of larger corals for industrial use, such as in cement factories, damages reefs.
  5. Mining and Quarrying: Coral reef mining conditions should be strictly enforced to prevent destruction.
  6. Human Activities: Firewood collection, grazing, trawling, dynamite fishing, and careless tourism contribute to reef damage.
  7. Souvenir Collection: Collection of shells and corals for ornamental trade, sometimes using dynamite, poses a threat to reefs.
Conservation Measures
  1. Legislation and Marine Parks: Establishing conservation legislation, marine parks, and reserves to protect coral reef areas.
  2. Awareness Programs: Forming marine conservation committees, conducting educational programs for various groups, and using audiovisual aids to raise awareness.
  3. Television Outreach: Conveying conservation messages to a wide audience through television.
  4. Local Initiatives: Implementing coral reef monitoring programs, scrutinizing coastal development projects, and developing local constituencies for reef protection.

Importance of Coral Reefs

  1. Coastal Protection: Coral reefs play a crucial role in protecting coastlines from erosive actions of sea waves.
  2. Habitat for Marine Species: Provide a habitat for numerous marine species, serving as areas for hiding, feeding, and reproduction.
  3. Resource Bank: Act as a source of food and medicine and store genetic resources.
The document Coral reefs and their formation | Zoology Optional Notes for UPSC is a part of the UPSC Course Zoology Optional Notes for UPSC.
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FAQs on Coral reefs and their formation - Zoology Optional Notes for UPSC

1. What is the definition of a coral reef?
A coral reef is a marine ecosystem formed by reef-building corals and other organisms, such as algae and sponges. It is characterized by a complex structure made up of calcium carbonate skeletons secreted by the corals.
2. How are coral reefs formed?
Coral reefs are formed over long periods of time through the accumulation and growth of coral polyps. These tiny animals secrete calcium carbonate to build their skeletons, which form the framework of the reef. As more and more corals settle and grow on top of the existing structures, the reef continues to grow.
3. What are the types of coral reefs?
There are three main types of coral reefs: - Fringing reefs: These are located close to the shore and directly attached to the coast or islands. - Barrier reefs: These are parallel to the coastline but are separated from the shore by a lagoon. - Atolls: These are circular or horseshoe-shaped reefs that surround a central lagoon and are usually found in the open ocean.
4. What are the factors contributing to the destruction of coral reefs?
Several factors contribute to the destruction of coral reefs, including: - Climate change and rising sea temperatures: Increased water temperatures can lead to coral bleaching, where the corals expel the algae living within them, causing them to turn white and become more susceptible to disease and death. - Pollution: Runoff from land, including sediment, chemicals, and nutrients from agriculture and urban areas, can negatively impact coral reefs by reducing water quality and promoting the growth of harmful algae. - Overfishing and destructive fishing practices: Overfishing can disrupt the delicate balance of the reef ecosystem, while destructive practices like using dynamite or cyanide to catch fish can directly damage the corals. - Coastal development and habitat destruction: Construction of resorts, ports, and other coastal infrastructure can lead to the destruction of coral reefs through dredging, sedimentation, and physical damage.
5. Why are coral reefs important?
Coral reefs are incredibly important for both marine and human life. They provide critical habitat for a wide variety of marine species, supporting biodiversity and acting as nurseries for many commercially important fish species. Coral reefs also act as natural barriers, protecting coastlines from erosion and storm damage. Additionally, they contribute to global carbon cycling by absorbing and storing large amounts of carbon dioxide, helping to mitigate climate change. Economically, coral reefs are valuable for tourism and fisheries, providing livelihoods for millions of people around the world.
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