Global Coral Bleaching Crisis

The world is currently facing an unprecedented coral bleaching crisis. The fourth global coral bleaching event (GCBE4) began in January 2023 and has surpassed previous records in scale and impact. As of April 2025, nearly 83.7 per cent of the world’s coral reefs are under severe heat stress, leading to widespread bleaching and potential coral mortality. The implications for marine biodiversity and human communities are severe, as many depend on coral reefs for food, tourism, and coastal protection.

About Coral Bleaching

Coral bleaching occurs when corals expel the symbiotic algae living in their tissues. This process is typically triggered by elevated sea temperatures. Without these algae, corals lose their colour and essential nutrients. Prolonged bleaching can result in coral death, disrupting entire reef ecosystems.

The Scale of the Current Event

GCBE4 has affected at least 15.5 per cent more reefs than the previous event, GCBE3, which occurred between 2014 and 2017. This previous event impacted 68.2 per cent of the world’s reefs. As of now, bleaching has been reported in 82 countries and territories, up from 74 just two years prior.

Data Collection and Challenges

Scientists are actively working to assess the full extent of coral mortality. In-water surveys are essential to quantify the damage accurately. Long-term monitoring at fixed sites helps establish a baseline for comparison. For instance, the Caribbean experienced severe bleaching in 2023 and 2024, and assessments are ongoing to determine coral loss.

Impact on Specific Regions

Preliminary surveys indicate coral mortality in various regions. The southern Great Barrier Reef experienced a 44 per cent loss in some protected zones. Similarly, the Chagos Archipelago reported a 23 per cent decline in live coral cover. High ocean temperatures have been recorded across multiple oceans, affecting reefs previously thought to be insulated from climate extremes.

The Role of Thermal Refugia

Thermal refugia are areas where coral reefs are less susceptible to bleaching due to cooler waters. However, even these regions, such as Raja Ampat in Indonesia and the Gulf of Eilat, have shown signs of bleaching. This marks the widespread nature of the crisis.

Assessments and Future Monitoring

Post-bleaching assessments indicate declines in coral cover. For example, Florida reported a 21 per cent drop in coral cover compared to the previous year. Studies from Mexico showed mortality rates between 50 per cent and 93 per cent across various coral species. Continuous monitoring is vital for understanding the ongoing impacts and recovery of coral ecosystems.

The Global Response

Experts stress the urgency of addressing climate change to mitigate coral bleaching. The ongoing crisis has prompted calls for immediate action to protect coral reefs globally. The situation is described as uncharted territory for the world’s reefs, necessitating concerted efforts from governments, scientists, and communities.

Questions for UPSC:

1. Discuss the implications of coral bleaching on marine biodiversity and human economies.
2. Critically examine the effectiveness of current global measures in combating climate change and its impact on marine ecosystems.
3. Explain the concept of thermal refugia in coral reefs and assess their role in resilience against climate change.
4. What are the long-term effects of coral reef degradation on coastal protection? Discuss with suitable examples.

Answer Hints:

1. Discuss the implications of coral bleaching on marine biodiversity and human economies.

1. Coral bleaching leads to the loss of habitat for numerous marine species, disrupting food webs.
2. Decreased biodiversity results in weakened ecosystem resilience, making recovery from environmental changes more difficult.
3. Human communities relying on reefs for fishing face food insecurity and economic challenges due to reduced fish populations.
4. Tourism industries are adversely affected, as coral reefs attract visitors for snorkeling and diving.
5. Coastal protection is compromised, increasing vulnerability to storms and erosion for communities living near reefs.

2. Critically examine the effectiveness of current global measures in combating climate change and its impact on marine ecosystems.

1. Current measures include international agreements like the Paris Agreement, but implementation remains inconsistent globally.
2. Many countries lack the resources to enforce climate policies effectively, leading to continued greenhouse gas emissions.
3. Marine protected areas are established but often inadequately enforced, limiting their effectiveness in preserving ecosystems.
4. Public awareness campaigns are increasing but may not translate into policy changes or individual actions.
5. Innovative solutions, such as coral restoration projects, are emerging but require substantial funding and long-term commitment.

3. Explain the concept of thermal refugia in coral reefs and assess their role in resilience against climate change.

1. Thermal refugia are areas where coral reefs are less susceptible to bleaching due to cooler water temperatures.
2. These regions provide a critical sanctuary for coral species during extreme heat events, enhancing survival rates.
3. Examples include Raja Ampat and the Gulf of Eilat, which have shown some resilience compared to surrounding areas.
4. However, recent bleaching events have affected even these refugia, denoting their vulnerability to climate change.
5. Conservation of thermal refugia is essential, but they alone cannot mitigate the broader impacts of climate change on marine ecosystems.

4. What are the long-term effects of coral reef degradation on coastal protection? Discuss with suitable examples.

1. Coral reefs act as natural barriers, absorbing wave energy and reducing coastal erosion.
2. Degradation leads to increased shoreline erosion, threatening infrastructure and habitats in coastal areas.
3. For instance, the loss of reefs in Florida has resulted in higher vulnerability to storm surges and flooding.
4. Communities that depend on reefs for protection face economic losses due to increased costs of artificial barriers and damage repairs.
5. Long-term degradation can lead to habitat loss for species that provide ecosystem services, further compounding issues related to coastal protection.