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Coral Bleaching

By: Ying Zhu

In recent years, Australia’s Great Barrier Reef has been hit by widespread coral bleaching repeatedly. It was reported that large parts of the reef had turned a ghostly white.

What is coral bleaching? Corals are usually light or golden brown, some may be bright blue, green, or even red and that can fluoresce. Their bright and vibrant colors are derived from the microalgae living within the coral. These microalgae help the coral survive by providing it with food resulting from photosynthesis. However, when the ocean environment changes, for example, if there are marine heat waves, the coral becomes stressed and expels the microalgae. Once the algae leave, the coral fades and turns white. It looks like it’s been bleached. Bleached corals are not necessarily dead. Corals can recover if conditions improve before they die. But when the water temperature stays high for a more extended period leaving no time for the coral to recover, the coral won’t let the algae grow back and eventually the coral will die. Once these corals die, reefs rarely come back.

Why does coral bleaching matter? Because coral reefs support the most biodiverse ecosystems in the world. They are often called the “rainforests of the sea”. Thousands of marine animals depend on coral reefs for survival, including sea turtles, fish, crabs, shrimps, jellyfish, birds, and many more. Coral reefs provide them shelter and protection from predators. They also provide food for the microorganisms at the base of ocean food chains. Once the reef ecosystems deteriorate and collapse, all the marine wildlife will be impacted. It will subsequently impact human food security regarding the availability of fish and crustaceans. Over half a billion people around the world depend on reefs for food, income, and protection. Coral reefs also protect coastlines from storms and erosion, provide jobs for local communities, and offer recreation opportunities. 

Australia’s Great Barrier Reef Bleaching is not an isolated phenomenon. Between 2014 and 2017, unusually warm waters (partially associated with a strong El Nino) affected 70% of coral reef ecosystems worldwide. The vast majority of the world’s coral reefs are at risk of disappearing. Scientists believe climate change is a whole host of bad things for corals. Back-to-back bleaching events have become more common in recent years as the climate gets hotter. However, researchers also observed some recovery in 2019 indicating that coral reefs are still resilient and will have the capacity to recover to pre-1998 if the pressure on the ecosystems can ease. We as a global community should make more environmentally conscious decisions to combat climate change. Our small, daily actions such as conserving energy, spreading the word, and continuously learning to find scientific, technological, and economic solutions to the present situation will make a difference and help to protect coral for future generations.

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