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

• Imperforate corals: Astraea, Flabellum, Favia, etc.
• Perforate corals: Porites, Madrepora, Montipora, Acropora, etc.

• Milliporans, Tubipora, Heliopora, alcyonarians like Fungia, gorgonarians.

• Mollusks, Foraminifera, sponges, sea anemones, various marine life like shrimps, crabs, lobsters, octopuses, etc.
• Reef fishes including sharks, eels, and rays.

• 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

• 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.

(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.

(3) Atoll:

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

Additional Types:

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

Theories Regarding Coral Reef Formation

• 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

• 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.

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.