Coral Bleaching

Published on 04 Apr 2025

Coral bleaching is a phenomenon whereby symbiotic algae called zooxanthellae, which reside within coral tissues, are expelled, causing coral colonies to lose their vivid colours.

Ideal Conditions for Coral Growth

• Sunlight: Shallow water with sunlight is ideal for coral growth. Corals rarely grow in depths greater than 165 feet (50 meters).

• Temperature: The ideal temperature range for the development of coral reefs is 23°C to 25°C. Water should not be warmer than 35°C.

• Saltwater: Clear saltwater is ideal for coral growth. Highly saline water and freshwater are not suitable for growth.

• Clean water: Corals are vulnerable to sediments and pollution. Sediments can create dirty water, obstructing the sun's light and damaging the polyps within.

Causes for coral bleaching

• Ocean Acidification: Increased CO2 levels in the atmosphere result in increased CO2 absorption by oceans, causing ocean acidification.

• Example: The Great Barrier Reef is facing the challenges of ocean acidification, primarily driven by the absorption of carbon dioxide (CO2) by seawater.

• Temperature Stress: High temperatures disrupt the symbiotic interaction between corals and zooxanthellae.

• Example: High temperatures and relentless marine heat waves triggered widespread coral bleaching and die-offs in the Florida Keys.

• Extreme Weather Events: Extreme weather events such as hurricanes and cyclones can physically harm coral reefs and raise stress, which increases the risk of bleaching.

• Example: In 2015, bleaching of the Chagos Archipelago in the Indian Ocean due to warming water and El nino conditions.

• Pollution: Coral bleaching may be worsened by water pollution from industrial discharges, agricultural runoff, and other human activities.

• Example: According to Cornell University, approximately 11 billion plastic items could be entangled in coral reefs in the Asia-Pacific region.

• Sedimentation: Construction near islands and the coast causes soil erosion, which raises the sedimentation and results in dirty water.

• Example: Red soil pollution on Coral Reefs in Okinawa, Japan

• Infectious Diseases: Bacterial infection may inhibit the photosynthesis of zooxanthellae which results in coral bleaching. 

• Example: Yellow-band disease on a coral formation off the coast of Samae San island in Sattahip district in the coastal Thai province of Chonburi.

Impacts of coral bleaching

• Reduced Light Penetration: Light penetration into coral reefs is decreased by suspended sediments in the water column which impacts the exchange of nutrients and energy between corals and algae.

• Example: Mass coral bleaching events of the Great Barrier Reef.

• Loss of Biodiversity: Bleaching events can disrupt the delicate ecological balance of these ecosystems, leading to declines in fish populations and other marine species.

• Example: According to journal Global Change Biology, shows that coral bleaching in 1998 has led to changes in biodiversity and permanent shifts in the range of fish species coexisting on coral reefs.

• Economic Consequences: Reduced coral health and the disappearance of vibrant underwater landscapes can deter tourists, which would result in economic losses.

• Example: The death of coral represents a huge loss—as much as $375 billion annually—for the local economies along the globe they support.

• Reduced Reproduction and Growth: Coral bleaching can have a detrimental effect on a coral's ability to reproduce, which can alter the quantity and quality of coral larvae produced.

• Disruption of food chain: Corals are the base of food chain in ocean, they support wide range of organisms.

• Example: A study in Papua New Guinea ref showed a decline in fish communities following declines in associated coral communities.

• Habitat loss: As dead coral colonies decompose, the three-dimensional complexity of the reef decreases, diminishing habitat availability for a variety of marine creatures.

• Example: Massive coral bleaching in Coastal Andaman Sea resulted in a rapid decline in coral calcification.

• Increased mortality: The entire reef ecosystem may be significantly impacted by severe or prolonged coral bleaching, which can cause coral death.

Government initiatives and policy measures

• Coastal Regulation Zone Notification (CRZ) 1991 under the EPA: No new construction is allowed in the CRZ-I (ecologically sensitive areas like mangroves, coral reefs, biosphere reserves etc.).

• Marine Protected Areas (MPAs): To protect certain areas of the nation’s waters, including some areas with coral reefs.

• Coral Bleaching Alert System: INCOIS uses satellite-derived Sea Surface Temperature (SST) to assess the thermal stress accumulated in the coral environs.

• National Committee on Mangroves and Coral Reefs: It was constituted in 1993 to advise the Government on relevant policies and programmes regarding marine species.

International initiatives

• International Coral Reefs Initiative (ICRI): It is an informal partnership between Nations and organizations which aims to preserve coral reefs and related ecosystems around the world.

• Global Coral Reef monitoring network: To provide scientific information and communication on the status of coral reef ecosystems to increase conservation and management for coral reefs.

• Coral Triangle Initiative: It is a multilateral partnership of six countries working together to sustain extraordinary marine and coastal resources.

• Glowing Glowing Gone campaign: The program is launched by UNEP on the loss of coral due to climate change.

Way Forward

• Preserve coral reef habitats: Create more marine protected zones and use sustainable fishing methods that avoid harming coral reefs.

• Water Quality Management: Set up and enforce policies to properly manage wastewater, minimize chemical contamination, and regulate industrial discharges.

• Climate Change Mitigation: Address the core causes of climate change, such as reducing greenhouse gas emissions, to mitigate the combined impact of pollution and climatic stresses on coral reefs.

• Monitor and assess coral health: Monitoring and evaluating coral health can help identify regions most vulnerable to coral bleaching and govern conservation efforts.

• Encourage public awareness: Spreading knowledge about the importance of coral reefs and encouraging eco-friendly practices like cutting back on carbon emissions and plastic waste.

Case study

Belize Coral Bleaching Response and Management Plan: To save the vibrant coral reef through community-based conservation.

Tags:
Environment

Keywords:
Corals Ecosystem Biodiversity Conservation Coral Bleaching

Syllabus:
General Studies Paper 3

Topics:
Biodiversity and Wildlife Conservation