Introduction to Coral Reefs
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- Coral reefs are hard, intricate, and colourful three-dimensional structures providing habitats for thousands of marine species including fish, invertebrates, sea turtles, and many other animals.
- Coral reefs are habitats for 25% of all marine species and are crucial for ecosystem balance.
- Found mostly in shallow coastal zones of tropical and sub-tropical oceans, coral reefs are among the world’s most diverse and productive ecosystems.
- Corals are formed by colonies of tiny organisms called polyps, which secrete layers of calcium carbonate to create protective crusts. These structures remain even after the polyps die, allowing other organisms to continue building the reef.
- Coral polyps and microscopic algae called zooxanthellae have a symbiotic relationship: polyps provide shelter while zooxanthellae provide food through photosynthesis and contribute to the reefs' colors.
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Types of Reefs
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Fringing Reefs
- Located near emergent land, they are shallow, narrow, and recently formed. They can be separated from the coast by a navigable channel.
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Barrier Reefs
- Broader and lie farther from the coast, separated by a stretch of water that can be several miles wide and tens of meters deep. Sandy islands sometimes form on top of these reefs.
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Atolls
- Ring-shaped reefs with a lagoon in the middle, often developed near the sea surface on underwater islands or sinking islands. The emergent part is typically covered with sediments and vegetation like coconut trees.
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Coral Reefs Distribution
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- Located in more than 100 countries, mostly between the Tropics of Cancer and Capricorn, including the Pacific Ocean, Indian Ocean, Caribbean Sea, Red Sea, and Persian Gulf.
- Cover an estimated area of 284,000 sq. km.
- Three major regions of development: Indo-Pacific, Wider Caribbean, and Red Sea.
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Cold Water Corals
- Have a hard skeleton and form huge reef structures in dark, deep, and cold waters. Lopheliapertusa is the only reef-forming coral in British waters.
- Found mainly on continental slopes off the west coast of Scotland at depths of 200-400 meters.
- United Nations Environment Programme reports more cold-water coral reefs worldwide than tropical reefs.
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Coral Reefs in India
- Located in the Gulf of Mannar, Palk Bay, Gulf of Kachchh, Andaman and Nicobar Islands, Lakshadweep Islands, Malvan coast, Netrani Island, and Gaveshani bank off the Mangalore coast.
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Factors Affecting Reefs
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- Sunlight: Corals need shallow water where sunlight can penetrate for the zooxanthellae algae to survive.
- Clear Water: Corals need clear water for sunlight to reach them; sediment and plankton can cloud water and reduce sunlight.
- Warm Water Temperature: Corals require warm water conditions (68–90°F or 20–32°C) to survive.
- Clean Water: Corals are sensitive to pollution and sediments, which can block sunlight and harm polyps.
- Saltwater: Corals need saltwater with a specific salt-to-water ratio to survive.
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Conservation Efforts in India
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- Environment (Protection) Act, 1986: Prohibits the use of corals and sands from beaches and coastal waters for construction.
- Coastal Regulation Zone Rules: Ban the collection and destruction of corals, along with dredging and underwater blasting.
- Marine Protected Area Network: Includes the Gulf of Mannar and Great Nicobar Biosphere Reserves, and Marine National Parks in the Gulf of Kachchh, Mahatma Gandhi Marine National Park, and Rani Jhansi Marine National Park.
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Threats to Coral Reefs
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- Coral reefs are vulnerable due to their slow growth and sensitivity to environmental changes.
- Coral Bleaching: Caused by ocean warming, leading to stress, ejection of zooxanthellae, and the death of corals.
- Sea-Level Rise: Slows coral growth and reduces sunlight exposure.
- Ocean Acidification: Hinders the ability of polyps to create reefs, making them weaker and more vulnerable.
- Storms: Frequent storms can damage reef structures faster than they can regrow.
- Other Threats: Destructive fishing, water pollution, unsustainable tourism, coastal development, sediment runoff, and coral mining.
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Causes of Coral Bleaching
- Solar Irradiance: Bleaching often occurs during summer at maximum sunlight exposure, especially in shallow waters.
- Sub-aerial Exposure: Sudden exposure to air during extreme low tides or tectonic uplift can cause bleaching.
- Sedimentation: Sediment loading can increase the likelihood of bleaching.
- Fresh Water Dilution: Storm-generated precipitation and runoff can cause bleaching, typically in small, near shore areas.
- Inorganic Nutrients: Increased nutrient concentrations can boost zooxanthellae densities, potentially leading to bleaching.
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Epizootics
- Pathogen-induced bleaching differs from other types; most coral diseases cause patchy or whole-colony death, resulting in a white skeleton rather than bleached tissues.
- Bleaching due to pathogens can affect a diverse range of coral hosts.
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Anthropogenic Impacts
- Human-induced disturbances like pollution, nutrient enrichment, and sedimentation are harmful to coral reefs.
- Human activities such as deforestation and poor land use practices increase the flow of freshwater, sediments, and pollutants to reef ecosystems.
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