Back-To-Back Mass Bleaching Decimates Australia's Great Barrier Reef

While U.S. President Donald Trump, who pulled out of the Paris climate agreement on June 1, is convinced global warming is a “hoax,” the deteriorating condition of the world’s coral reefs seems to suggest otherwise. Often called “rainforests of the sea,” the incredible ecosystems that occupy less than 0.1 percent of ocean’s surface are home to almost 25 percent of all marine species. Unfortunately, the rising ocean temperatures caused by global warming are wreaking havoc on these fragile organisms.

As you may know, the colorful coral reefs that we all admire, are calcium carbonate exoskeletons that provide shelter and protection to colonies of hundreds of thousands of tiny polyps that live and grow together. To survive, the sedentary animals have developed a symbiotic relationship with the zooxanthellae. The coral polyps give the algae a home in exchange for the beautiful colors and nutrition. However, when ocean temperatures rise, the coral polyps reject the zooxanthellae, losing both their food source and vivid coloring; a phenomenon researchers refer to as “bleaching.” While the tiny animals can recover from mild bleaching, they are unable to survive when it continues for an extended period.

Though the warmer temperatures are impacting coral reef systems worldwide, none have been as devastated as the Great Barrier Reef, that lies off the coast of Queensland, Australia in the Coral Sea. Over the past twenty years, the beautiful ecosystem that is home to over 1,500 species of fish has suffered through four mass “bleaching” events – 1998, 2002, 2016 and now again in 2017.

The 2016 bleaching was the result of the El Niño, a natural warm weather condition which occurs periodically every 3-5 years across the equatorial Pacific Ocean. Initial aerial and in-water surveys indicated that it damaged 22 percent of the shallow water corals, the most destruction recorded in the history of the Great Barrier Reef.

In March and April 2017, the ecosystem suffered a second mass bleaching event. This time around, however, there was no El Niño, and the phenomenon is entirely attributed to warmer ocean temperatures caused by climate change. Current estimates peg the damage to 500 km (310 miles) of the central portion of the reef which was largely spared last year. Additionally, a report released on May 29 found that the 2016 damage was even worse than had been previously believed, impacting an astounding 29 percent of the 2,300 km (1,400 mile) long World Heritage site reef.

To make matters worse, tropical cyclone Debbie, which could have rescued the reefs by cooling the waters, not only came in late but also added to the destruction by causing structural damage to a section which had miraculously escaped the worst of the bleaching. Marine experts say almost half of the reef is now "extremely" bleached, and 91 percent shows at least some signs of bleaching.

Given that it takes more than a decade for the bleached corals to be re-colonized by the algae after the water temperatures return to normal, researchers believe it is unlikely that the Great Barrier Reef will ever fully recover. Great Barrier Reef Marine Park Authority (GBRMPA) Chairman Russell Reichelt says, "We're very concerned about what this means for the Great Barrier Reef itself and what it means for the communities and industries that depend on it,"

While local measures such as preventing water pollution and restricting port development can help, they are not enough to save the the reef, which is already under extreme heat stress. The only solution, therefore, is a global action to reduce greenhouse gas emissions by curbing fossil fuel burning, something that the 194 countries still part of the Paris climate agreement have vowed to do. If they do not live up to their promise, we may become the only generation in history to have witnessed both the beauty and death of the largest living structure on Earth – the Great Barrier Reef!

Resources: news.nationalgeographic.com, guardian.co.uk, phys.org