The Great Barrier Reef is Experiencing Its 6th Mass Bleaching Event
Bleaching indicates that corals are under extreme stress, often from warming water. Despite their plant-like appearance, corals are animals made up of hundreds to thousands of tiny creatures called polyps that rely on photosynthetic algae that live in their tissues to produce food. But when corals are stressed by warm marine waters, they will expel their algal partner in a process called coral bleaching. The corals turn a stark white, and if stressed for too long, they will die.
The Great Barrier Reef is the largest coral reef system in the world, stretching for 1,429 miles over an area of approximately 133,000 square miles. The sprawling ecosystem is made up of individual reefs formed over thousands of years, which have been repeatedly stressed by recent marine heatwaves. While they can recover if temperatures cool, roughly 30 percent of the corals on the Great Barrier reef died after the last mass bleaching in 2016. Corals are under increasing stress from climate change and greenhouse gas emissions, which helped make the last year the hottest on record for the world's oceans. Between 2009 and 2019, 10% of the world's coral reefs were lost.
Water temperature on the reef soared as high as seven degrees Fahrenheit above average in recent weeks. This year’s intense bleaching event is the first since 2020 when over a third of corals had moderate bleaching and a quarter had severe bleaching. Because the previous heatwave was short-lived, many of the bleached corals were able to recover.
Longer and more frequent bleaching events are only expected to become increasingly common as human-caused climate change warms the planet. The more severe a marine heatwave, the less likely corals are to recover from bleaching. We need to really learn from these bleaching events and change business as usual.
There is good progress happening to address coral challenges, such as focusing on corals with robust genes that could make them natural candidates for restoration projects. For example, in the Bahamas, a research biologist from Chicago’s Shedd Aquarium, is focusing on corals with robust genes that could make them natural candidates for restoration projects. He recently published a study of two Bahamian reefs, one that seemed to survive an intense 2015 heat wave, and one that didn’t. There is also evidence of corals evolving more quickly in the past two decades to withstand rapidly warming temperatures. The big question scientists are now investigating is whether there’s a cap on how much more heat corals can adapt to. These regions with heat-adapted corals are referred to as “super reefs,” and some advocate for using marine reserves to protect them.
