The Third Mass Bleaching Event on the Great Barrier Reef
Sophie McDonald
This summer (in the southern hemisphere), a quarter of the Great Barrier Reef was severely bleached in the third mass bleaching event in five years. Immediate climate action is the solution to these back-to-back tragedies. We delve into the main causes of this mass bleaching event, why these events threaten ocean ecosystems, and what we as individuals can do to help.
Coral reefs house the highest biodiversity of any ecosystem on Earth and directly support half a billion of the world’s population. The iconic Great Barrier Reef is the world’s largest coral reef system. It is recognised as one of the seven natural wonders of the world, which means it is our shared responsibility to preserve it.
Our beautiful Great Barrier Reef is home to a wide array of marine life. Photo: Underwater Earth / XL Catlin Seaview Survey / Christophe Bailhache.
In March of this year Prof Terry Hughes, director of the Centre of Excellence for Coral Reef Studies, completed surveys of the reef and found one quarter of the Great Barrier Reef was severely bleached. Corals were affected in all three regions (north, central, south) of the reef, making this the most widespread bleaching event since mass bleaching outbreaks were first reported in 1998. This is the fifth mass bleaching event to hit the Great Barrier Reef. Following outbreaks in 2016 and 2017, this event was the third to take place within the last five years.
What exactly is coral bleaching?
Firstly, what are corals? Corals are animals and those that most people are familiar with are tropical, shallow water, reef-building corals, comprised of a calcium carbonate skeleton. They have a symbiotic relationship with tiny, colourful algae called zooxanthellae that live in their tissues which provide essential nutrients.
Bleaching takes place when there are extreme changes in water conditions, such as a change in temperature, light, or nutrients. When this occurs corals become stressed and they expel their zooxanthellae, which causes them to turn completely white.
Bleached corals are not dead, as they can recover if conditions rapidly return to normal. However, if the stress continues and the algae loss is prolonged, the coral will eventually die due to a lack of nutrients.
Corals get their distinctive bright appearance from the colourful algae living in their tissues. These algae are expelled during bleaching, causing corals to turn white. Photo: Underwater Earth / XL Catlin Seaview Survey / Lynton Burger.
Why did this mass bleaching event happen?
Human activities have caused average global temperature to rise about 1°C above pre-industrial levels, causing marine heatwaves and triggering more frequent and more severe mass bleaching events. The UN has warned that 1.5°C warming will result in up to 90% of the world’s coral reefs being lost.
In February 2020, the Great Barrier Reef was subjected to the hottest sea surface temperatures since records began in 1900, leading to a widespread bleaching event.
Current trends suggest that we are heading towards more than 3°C of warming. In this scenario we send all of the world’s tropical corals to a colourless grave. We cannot allow this to happen.
Why does it matter?
Losing our biologically rich coral reefs means losing a devastating amount of ocean life. Although reefs cover less than 0.1% of the ocean floor, they house over a quarter of all marine fish species as well as a whole host of other marine animals.
Coral reef ecosystems also provide a wide range of economic and social services including fisheries and coastal protection as well as recreation and tourism. Calcium carbonate reef-building organisms have an important role as a carbon sink (as CaCO₃) with rates of up to 90 million tonnes of carbon per year. Reefs are also medicinal treasure troves and their chemical compounds have yielded treatments for cardiovascular diseases, ulcers, and cancers.
Protesting is a great way to involve yourself in climate action. When it is safe to do so, why not get involved in a climate protest in your local area? Photo: Markus Spiske (Unsplash).
What can we do to help?
To save our corals we must combat climate change.
In order to save our precious corals we have to get serious about bringing a halt to global warming by turning off the tap of greenhouse gas emissions. There is no stopping global warming at this point, however we must act now to reduce its impact as much as possible. As climate activist Greta Thunberg puts it, we must “try to save what we can save”.
Climate action must be complimented with combative measures such as improving water quality and controlling outbreaks of harmful crown of thorns starfish (which eat coral) to improve reef resilience, as well as continuing research into coral heat tolerance.
Each of us must ramp up our climate activism and weave it into every aspect of our daily lives, making drastic changes in our personal lives as well as calling on our governments to act. As an individual you can also make your life more coral-friendly by using reef-friendly sunscreen, supporting reef-friendly coastal businesses, and supporting marine conservation organisations.
Our corals are sending a bright, white cry for help. Let’s answer it.
Find out more about what you can do to tackle climate change.