Catastrophic Coral Bleaching in the Great Barrier Reef

In May 2024, the southern Great Barrier Reef (GBR) experienced a catastrophic coral bleaching event. This event resulted in a shocking 44 per cent mortality rate among corals in protected areas. This mass bleaching was triggered by heat stress linked to the fourth global coral bleaching (GCBE4) event that began in January 2023. This incident surpassed previous bleaching events, with 77 per cent of global reefs suffering from heat-induced stress.

Coral Bleaching Explained

Coral bleaching occurs when corals expel the symbiotic algae known as zooxanthellae. This process is a response to environmental stress, particularly increased water temperatures. When corals bleach, they turn white and lose their primary source of nutrition. While some corals can survive bleaching, prolonged stress can lead to death.

Impact of Heat Stress

In January 2024, researchers monitored 462 coral colonies at One Tree Reef. They recorded peak temperatures of 30.55°C. By February, 66 per cent of the colonies showed signs of bleaching. This figure increased to 80 per cent by April. By May, 44 per cent of the bleached colonies had died. Mortality rates increased to 53 per cent by July.

Extent of Damage

Certain coral genera, such as Acropora, faced catastrophic mortality rates of up to 95 per cent. Even corals previously deemed resilient, like Porites, experienced bleaching. The heat stress made corals more susceptible to diseases, exacerbating mortality rates. For instance, Goniopora corals developed black band disease, contributing to the high death toll.

Coral Health Decline

The rapid decline in coral health is unprecedented for the GBR. By July, mortality rates soared, particularly in Isopora and Goniopora colonies. As coral colonies collapsed, parts of the reef transformed into rubble. The structural integrity of the reef was compromised, with Acropora and Seriatopora showing alarming mortality rates.

Consequences for Ecosystems

Frequent bleaching events challenge the reef’s ability to recover. This leads to shifts in species composition and overall ecosystem structure. The research puts stress on the urgent need for effective management strategies to safeguard coral reefs. These ecosystems play important role in biodiversity, food security, and coastal protection.

Urgent Calls for Action

Scientists, including lead author Maria Byrne, stress the need for immediate action to protect coral reefs. Despite being in protected areas, the GBR was severely impacted by extreme heat stress. Researchers advocate for prioritising strategies that enhance the resilience of coral reefs against climate change.

Questions for UPSC:

1. Critically analyse the implications of coral bleaching on marine biodiversity and coastal economies.
2. What strategies can be implemented to enhance the resilience of coral reefs against climate change? Discuss.
3. Point out the relationship between sea surface temperature rise and the frequency of coral bleaching events.
4. Estimate the potential long-term impacts of coral reef degradation on global fisheries and food security.

Answer Hints:

1. Critically analyse the implications of coral bleaching on marine biodiversity and coastal economies.

1. Coral reefs are biodiversity hotspots, providing habitat for numerous marine species; their decline threatens these ecosystems.
2. Loss of coral leads to reduced fish populations, directly impacting local fisheries and food supplies for coastal communities.
3. Tourism, heavily reliant on healthy reefs, suffers from bleaching events, leading to economic losses in coastal regions.
4. Coral bleaching undermines ecosystem services such as coastal protection, increasing vulnerability to erosion and natural disasters.
5. Long-term biodiversity loss can disrupt ecological balance, leading to shifts in species composition and function.

2. What strategies can be implemented to enhance the resilience of coral reefs against climate change? Discuss.

1. Establishing marine protected areas (MPAs) to limit human activities that stress coral ecosystems.
2. Implementing restoration projects, such as coral gardening and artificial reefs, to rehabilitate damaged areas.
3. Enhancing monitoring and research to understand coral responses to climate stressors and improve management practices.
4. Reducing local stressors, like pollution and overfishing, to help corals withstand global climate changes.
5. Promoting community engagement and education to encourage conservation efforts and sustainable practices among coastal populations.

3. Point out the relationship between sea surface temperature rise and the frequency of coral bleaching events.

1. Increased sea surface temperatures directly correlate with coral stress, leading to bleaching events.
2. The fourth global coral bleaching event (GCBE4) was triggered by elevated temperatures, surpassing previous records.
3. As global temperatures rise due to climate change, the frequency and severity of bleaching events are expected to increase.
4. Heat stress from temperature spikes causes corals to expel zooxanthellae, resulting in bleaching and potential mortality.
5. Monitoring sea surface temperatures helps predict and manage coral bleaching risks, informing conservation efforts.

4. Estimate the potential long-term impacts of coral reef degradation on global fisheries and food security.

1. Coral reefs support about 25% of global marine species, and their degradation threatens fish populations crucial for food security.
2. Declining fish stocks from reef degradation can lead to increased food scarcity and economic instability in coastal communities.
3. Loss of biodiversity affects ecosystem resilience, reducing the ability of fisheries to recover from overfishing and environmental changes.
4. Coral reef degradation can disrupt breeding and nursery habitats for many fish species, impacting future populations.
5. Long-term impacts may include increased reliance on alternative protein sources, affecting nutrition and health in vulnerable populations.