The Great Barrier Reef (GBR) is in the grip of the 5th mass coral bleaching event in only 8 years. Widespread mass bleaching of the Great Barrier Reef was first seen in 1998 and happened again in 2002, 2016, 2017, 2020, 2022 and now in 2024.
Current Bleaching
- The bleaching was being driven by global heating and an El Niño climate pattern. The scientist observed that climate change is the greater threat to the GBR and other coral reef ecosystems across the world’s oceans.
What are corals?
- Corals are invertebrate animals belonging to a large group of colourful and fascinating animals called Cnidaria.
- Each individual coral animal is called a polyp, and most live in groups of hundreds to thousands of genetically identical polyps that form a ‘colony’.
- Hard corals extract abundant calcium from surrounding seawater and use this to create a hardened structure for protection and growth.
- Coral reefs are created by millions of tiny polyps forming large carbonate structures, and are the basis of a framework and home for hundreds of thousands of other species.
- Coral reefs are the largest living structure on the planet, and the only living structure to be visible from space.
- Coral polyps have developed this relationship with tiny single-celled plants, known as zooxanthellae. Inside the tissues of each coral polyp live these microscopic, single-celled algae, sharing space, gas exchange and nutrients to survive.
What is coral bleaching?
- Coral and algae depend on each other to survive. Corals have a symbiotic relationship with microscopic algae called zooxanthellae that live in their tissues.
- When corals bleach due to higher than average ocean temperatures, they expel the algae that lives inside them and gives them much of their nutrients and colour.
- Without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease.
- If temperatures fall, corals can survive but scientists say they tend to be more susceptible to disease and struggle to reproduce. In extreme cases of heat stress, corals can die.
Causes of coral bleaching?
- Increased ocean temperature caused by climate change is the leading cause of coral bleaching.
- Runoff and pollution Storm generated precipitation can rapidly dilute ocean water and runoff can carry pollutants — these can bleach near-shore corals.
- When temperatures are high, high solar irradiance contributes to bleaching in shallow-water corals.
- Exposure to the air during extreme low tides can cause bleaching in shallow corals.
Great Barrier Reef
- The Great Barrier Reef in Australia is the biggest coral system in the world.
- It is about 2,300km long, covers an area bigger than the size of Italy and is made up of about 3,000 individual reefs.
- It is a UNESCO World Heritage site.
(Sources: NOAA, icriforum, The Guardian)
