What is Marine Heatwaves? UPSC

Why in News? A major 24-year-long coral reef monitoring study in the Lakshadweep archipelago, conducted by the Nature Conservation Foundation, has revealed a significant 50% decline in coral cover since 1998 due to repeated marine heatwaves driven by climate change.

Key Points:

1. Study Details:
   • Published in the journal Diversity and Distributions.
   • Title: “Local Environmental Filtering and Frequency of Marine Heatwaves Influence Decadal Trends in Coral Composition”.
   • Based on long-term monitoring (1998–2022) of coral reefs at Agatti, Kadmat, and Kavaratti atolls in Lakshadweep.
2. Key Findings:
   • Coral cover declined from 37.24% in 1998 to 19.6% in 2022.
   • Represents a ~50% decline in coral reef health over 24 years.
3. Causes:
   • Repeated marine heatwaves due to El Niño Southern Oscillation (ENSO) events in 1998, 2010, and 2016.
   • Intensified by global climate change.
4. Recovery Patterns:
   • Reduced recovery rates after each bleaching event, though coral mortality decreased with successive events.
   • Critical recovery period identified: At least six years of bleaching-free conditions are needed for significant coral regeneration.
5. Local Factors Matter:
   • Recovery varies depending on wave exposure, depth, and other site-specific environmental filters.
6. Predictive Framework:
   • Study offers a predictive model to identify vulnerable vs. resilient reefs, aiding in conservation planning.

About Marine Heatwaves:

Definition:

Marine heatwaves (MHWs) are prolonged periods of unusually high sea surface temperatures (SSTs) in a particular ocean region. These events typically last for days to months and can extend over hundreds to thousands of kilometers.

Key Features of Marine Heatwaves:

Causes of Marine Heatwaves:

1. Climate Change:
   • Increases global ocean temperatures, making heatwaves more frequent and intense.
2. Atmospheric Blocking & High-Pressure Systems:
   • Trap heat near the ocean surface and reduce cooling.
3. El Niño Events:
   • Trigger large-scale warming in the Pacific, influencing global marine heatwaves.
4. Reduced Ocean Mixing:
   • Less vertical movement of cold water weakens natural ocean cooling.

Impacts of Marine Heatwaves:

Examples of Marine Heatwaves:

• Lakshadweep Archipelago: Repeated heatwaves since 1998 caused ~50% coral decline.
• The Blob (2013–2016): A massive Pacific Ocean marine heatwave causing widespread ecological disruption.
• Great Barrier Reef (Australia): Severely bleached during marine heatwaves in 2016, 2017, and 2020.

Possible Solutions / Way Forward:

1. Global climate action to reduce greenhouse gas emissions.
2. Marine Protected Areas (MPAs) to reduce local stressors.
3. Coral restoration projects using heat-resistant species.
4. Early warning systems using satellite and ocean data.
5. Strengthening local governance and community-based adaptation.