Understanding Coral Bleaching: Threats to the Great Barrier Reef
Context: A recent study published in Geophysical Research Letters highlights the Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO) as major factors influencing coral bleaching in the Great Barrier Reef (GBR).
Key Findings
- Corals in the GBR are susceptible to weather conditions, with sunny, calm weather leading to increased ocean temperatures and higher risks of coral bleaching.
- Conversely, stormy and rainy weather can cool the ocean by promoting the mixing of cooler deeper waters with warmer surface waters, providing some protection to corals.
- The study highlights that while the ENSO influences GBR weather seasonally, the MJO affects weather on shorter timescales, causing unexpected fluctuations in ocean temperatures that impact coral health.
Implications for Future
- Understanding the influences of ENSO (El Niño and La Niña) and MJO on weather patterns is crucial for predicting coral bleaching events in the GBR.
- ENSO phases traditionally affect ocean temperatures, with El Niño often leading to increased coral bleaching risk and La Niña potentially providing cooler conditions, though recent observations challenge this expectation.
- The MJO, influencing sub-seasonal weather variability, can disrupt typical ENSO patterns that impact coral health.
What is Coral Bleaching?
When corals are under stress, they expel the microscopic algae that live in their tissues. Without these algae, corals’ tissues become transparent, exposing their white skeleton. This process is called coral bleaching. Bleached corals are not dead but are more at risk of starvation and disease.
Causes of Coral Bleaching:
- The primary cause of coral bleaching is rising ocean temperatures due to climate change. Even a temperature increase of just one degree Celsius for four weeks can trigger bleaching.
- Other Environmental Stressors: Changes in water quality, increased sun exposure, and extremely low tides can also cause corals to bleach.
- Climate Patterns and Coral Bleaching: El Niño Southern Oscillation and Madden-Julian Oscillation.
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- ENSO, a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean, influences weather patterns over the GBR on a seasonal scale.
- MJO, a major fluctuation in tropical weather on shorter, sub-seasonal timescales, can alter weather patterns over the GBR unexpectedly. It impacts ocean temperatures and corals.
Recent Mass Bleaching Events:
- 2024: The fifth mass bleaching event on the GBR was confirmed in March 2024. It occurred during an El Niño year and followed the hottest year on record.
- 2022: Bleaching occurred along the length of the Reef, with extreme bleaching in the Northern and Central regions. The event was particularly concerning because it occurred during a La Niña summer.
- 2020: Widespread severe bleaching affected many regions of the GBR. On-water monitoring capabilities were restricted due to the COVID-19 pandemic.
The Great Barrier Reef (GBR) spans nearly 350,000 square kilometres along Australia’s northeastern coast, making it the largest coral ecosystem globally.
- This reef is located between 9 degrees south to 22 degree south latitudes and stretches for a length of 1200 miles and covers about two-thirds of the coastal length of Queensland province of Australia.
- It is known for its rich biodiversity, cultural importance, and economic significance.
- It contributes approximately $6.4 billion annually to the Australian economy.
- They are facing significant threat challenges from rising ocean temperatures caused by climate change.
- Important habitat for endangered species such as dugongs and green turtles.
- Balancing conservation with tourism, fishing and other human activities is a complex challenge.
