Coral Bleaching

Imagine a beautiful underwater garden filled with colourful corals, bustling with marine life. Suddenly, this vibrant ecosystem turns pale, as if all life is draining away. This is coral bleaching, a phenomenon that signals extreme distress in coral reefs.

What is Coral Bleaching?

Coral bleaching occurs when corals lose their symbiotic algae, called zooxanthellae. These microscopic algae provide corals with:

1. Food (through photosynthesis), and
2. Colour (giving corals their bright hues).

When stressed, corals expel these algae, leading to:

• Loss of colour → Corals appear white or “bleached.”
• Loss of food → Corals weaken, and if stress continues, they die.

Causes of Coral Bleaching

Corals are extremely sensitive to changes in their environment. Here’s what triggers bleaching:

1. Global Warming

• Corals thrive within a narrow temperature range (23-29°C).
• Rising sea temperatures due to climate change stress corals, forcing them to expel zooxanthellae.
• Even a 1-2°C rise can cause widespread bleaching!

2. Ocean Acidification

• Excess CO₂ dissolves in seawater, forming carbonic acid, which:
  • Lowers pH levels → Oceans become more acidic.
  • Weakens coral skeletons, making them more fragile.

3. Silt Deposition from Rivers

• Increased glacial melting (due to climate change) leads to more silt (fine soil particles) flowing into the ocean.
• This clogs coral pores, blocking sunlight and reducing oxygen supply.

4. Freshwater Dilution (Due to Heavy Rainfall)

• More rainfall = More freshwater in oceans, reducing salinity (salt content).
• Corals are adapted to a specific salinity level; lower salinity stresses them, leading to bleaching.

5. El Niño Events

• El Niño causes unusual warming of ocean waters, leading to:
  • Extreme sea temperature rise → Mass coral bleaching.
  • Lower upwelling of nutrients, reducing coral health.

6. Subaerial Exposure (Temporary Exposure to Air)

• If corals are suddenly exposed above water due to:
  • Extreme low tides, or
  • Tectonic uplift (land rising due to earthquakes, etc.),
  • They dry out and bleach.

7. Eutrophication (Nutrient Overload in Water)

• Excess fertilizers from agriculture run into oceans, increasing nutrient levels.
• This causes algae overgrowth, blocking sunlight and choking corals.

8. Marine Pollution

• Oil spills, industrial waste, sewage discharge, and plastic pollution degrade coral health.
• Toxins poison corals and their zooxanthellae, leading to bleaching.

9. Coral Mining & Destruction

• Corals are often mined for:
  • Decorative purposes (jewelry, souvenirs).
  • Building materials (used in cement and construction).
• Mining directly kills corals, while dredging disturbs the ecosystem.

Why Should We Care?

Coral reefs are not just pretty underwater structures—they are essential for marine life and humans! 🌏

Ecological Importance

• 25% of all marine species depend on coral reefs.
• They act as barriers against coastal erosion and protect shorelines from storms and tsunamis.

Economic & Human Impact

• Reefs support fishing & tourism industries.
• Their destruction leads to loss of livelihood for millions.

Can Coral Bleaching Be Reversed?

🔄 If stressors disappear quickly, corals can recover by reabsorbing zooxanthellae.
❌ If stress continues, corals die, leading to irreversible reef loss.

Australia’s Great Barrier Reef

• The Great Barrier Reef, with over 2,900 individual coral reefs, is the world’s largest reef system, located in the Coral Sea, off Queensland, Australia.
• It is the largest single structure made by living organisms and is visible from outer space.
• The reef is a habitat for the dugong (sea cow) and green turtle. It was inscribed as a World Heritage Site in 1981.
• According to IUCN, the Great Barrier Reef is in a “critical state and deteriorating” due to climate change and warming waters.
• Its conservation status has been downgraded from “significant concern” to “critical” because of frequent mass bleaching events (four in the past six years).
• An UN-backed mission has recommended that the reef be added to the list of endangered World Heritage sites (not yet implemented).

The Threat of Coal Mining

• Australia is one of the largest exporters of fossil fuels. The reef faces threats from coal mining, gas extraction, and port construction for mining ships.
• In 2018, the Australian government approved Adani’s $16.5 billion Carmichael coal-mining project in the Galilee Basin, Queensland — one of the largest untapped coal reserves.
• The mine is connected to Abbot Port (operated by Adani) and produces thermal coal (for power generation) and metallurgical coal (for steel making). The project sparked massive protests.
• In February 2023, Australia — highly dependent on coal for electricity — rejected a new coal mining application for the first time, citing its potential harm to the Great Barrier Reef.
• The proposed open-pit mine would have damaged fragile seagrass meadows, vital feeding grounds for dugongs.

Biorock Technology for Coral Restoration

• The Zoological Survey of India attempted coral reef restoration using biorock technology in the Gulf of Kachchh.
• Biorock is formed by mineral accretion (electro-accumulation of minerals) on steel structures placed on the seabed and connected to a power source (e.g., floating solar panels).
• A small electric current flows between the anode (+) and cathode (–) on the sea floor.
• This causes calcium ions to combine with carbonate ions, depositing calcium carbonate (CaCO₃) on the cathode. The electro-accumulated CaCO₃ is termed biorock.
• Fragments of broken corals are tied to the biorock structure. Coral larvae adhere to the CaCO₃ and grow faster, as they need not expend energy building their skeletons.

Final Thought ⏳

Coral bleaching is a warning sign from the ocean—a cry for help. If we don’t act now, we may lose these natural wonders forever.

What Can We Do?

• Reduce carbon emissions (limit global warming).
• Prevent marine pollution (reduce plastic waste, regulate industrial discharge).
• Protect coastal ecosystems (stop deforestation & unsustainable fishing practices).

Saving coral reefs isn’t just about preserving beauty—it’s about securing our planet’s future! 🌍✨