One of the most common questions we receive about the Great Barrier Reef is ‘what is coral bleaching?’ In recent years the Great Barrier Reef has been subject to media reports of large scale bleaching events. This article aims to provide you with a coral bleaching 101! Covering what bleaching is, what causes corals to bleach, as well as busting a few myths and misconceptions that we hear whilst out on the water!
To fully understand coral bleaching, you must first understand what coral is. We recommend reading this short article ‘What is Coral?‘ before going too much further!
Coral bleaching is a stress response. When the coral is stressed, the relationship between the polyp and the algae begins to weaken. The chemicals produced by the algae that typically feed the polyp change, and actually become harmful to the animal. As a result, the polyp expels the algae as a defensive response. No algae, no colour, and the corals appear a vibrant white colour, hence the name bleaching.
What causes Coral Bleaching?
So, what causes coral bleaching? Coral is an incredibly intricate system and environmental change can cause a great deal of stress to coral reefs. For example, an increase or decrease in temperature, too much or too little sunlight, an abundance of nutrients or excessive fresh water can all cause coral bleaching. However, the only thing we know to cause large scale mass bleaching is temperature stress.
Is Bleached Coral Dead Coral?
No, it is not. A common misconception with coral bleaching is that bleached coral is dead coral. That’s not the case. However, a coral polyp without the algae is essentially like me removing up to 90% of your food. Before long, you will get hungry, and you’re not going to survive for a sustained amount of time. If, however the conditions improve, the polyps can once again recruit the algae and can continue the process of growing on the reef. If the circumstances remain unfavourable for an extended period of time, unfortunately that coral is unable to survive.
Why is this important?
In 2016 and 2017, we saw widespread coral bleaching. Unfortunately, in many parts of the Great Barrier Reef, large sections of the reef did not survive. The less coral we have on the reef, the less diversity, and the less reproduction of future corals during coral reproduction events (Coral Spawning). Once again, this does not mean the reef in these parts are dead. However, the fewer surviving corals are responsible for repopulating a larger area. If the conditions are not optimal for a substantial amount of time, it becomes tough for these reefs to recover.
The long-term effect of these mass bleaching events are devastating, and managing global issues such a Climate Change is essential for the future of coral reefs all across the world. In 2020 another mass bleaching event was announced by the Great Barrier Reef Marine Park Authority, however, here in the Whitsundays, we are pleased to report a good success rate in terms of coral recovery. For information on this recovery see the relevant Whitsunday Reef Health Update.
How can you help?
As mentioned before, bleached coral, does not mean dead coral! It is now more important than ever to ‘See the Reef, Love the Reef and Protect the Reef’. Jump on either our Northern Exposure or Southern Lights tour to see the wonders of the Whitsundays and the Great Barrier Reef and see for yourself that the reef remains a vibrant environment well worth protecting.
In terms of protecting it, everyone can play their part, no matter how small. Engage in citizen science projects like Eye on the Reef, reducing your carbon footprint or cut out single-use plastics. Everyone can play their part to ensure the Great Barrier Reef remains a beautiful environment for future generations to enjoy.