The Great Barrier Reef, the world’s largest coral reef system, is characterized as the biggest structure ever built by living creatures. It is home to over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometers. Each of them was formed for over millions of years from the skeletons and skeletal waste of a mass of living marine organisms. Hundreds of life forms which include a great variety of marine life rely on the Great Barrier to survive.
Severe Mass Bleachings Throughout the Years
Unfortunately, just like other ecosystems, the Great Barrier Reef is extremely threatened by the climate crisis. Previous reports showed that severe regional bleaching used to hit the reef about every 27 years. But, since the 1980s, the pace has accelerated to every six. Even in the best conditions, badly damaged reefs take at least 10 years to rebound. Mass coral bleaching is the major reason why the Great Barrier Reef is at risk of dying. It occurs when unnaturally hot ocean water destroys a reef’s colorful algae, leaving the coral to starve.
Since 2016, half of the Great Barrier Reef has been bleached to death. As a result, much of the marine ecosystem along the reef’s north coast has become barren and skeletal with little hope of recovery. A 2019 study published in Nature revealed that the number of new corals on the Great Barrier Reef crashed by 89% after the climate change-induced mass bleaching of 2016 and 2017. Lead author Terry Hughes, a coral scientist from the ARC Centre of Excellence for Coral Reef Studies at James Cook University, said that the results showed an uncertain picture for the reef in years to come.
According to The Guardian, a British daily newspaper, the researchers have measured how many adult corals survived along the length of the world’s largest reef system as well as how many new corals they produced in 2018 in the aftermath of severe heat stress and coral mortality. “We’ve told the story of coral dying, we’ve told the story of some being winners and losers. Now we’ve got the next phase where species have a chance to recover. But what we’re seeing is that it’s happening a lot slower because we only have 10% of the babies,” Hughes said.
The researchers found out that while there has been a small increase in new corals in the southern-most sections of the reef, they measured an 89% drop in new corals across the entire reef. The mix of species that make up the pool of coral babies has also shifted dramatically. Acropora, for instance, the reef’s dominant species, declined by 93%. “We’re not saying the Barrier Reef is doomed, but it is on a new trajectory. The way it’s connected, the mix of species, it’s all changing,” Hughes said.
The Worst Bleaching To Date
Unfortunately, mass bleachings don’t stop there. Recently, scientists reported that the Great Barrier Reef experienced a third mass coral bleaching event in five years. This follows the worst outbreaks of mass bleaching on record on the world’s biggest reef system in 2016 and 2017. The team, also led by Hughes, assessed bleaching levels on 682 reefs from a spotter plane flying at about 500 feet. Results of the aerial surveys revealed a mixed picture of the Great Barrier Reef: some severe bleaching on reefs are closer to shore, while outer “ribbon reefs” in the far north escaped damage.
The findings of the report suggested that majority of tropical coral reefs would disappear even if global temperature was limited to 1.5 Celsius. “We know enough now that [the bleaching] is more severe than in 1998 and 2002. How it sits with 2016 and 2017 we are not sure yet,” Hughes said.
According to EcoWatch, a leading environmental news site engaging millions of concerned individuals every month, the 1998 and 2016 bleachings occurred during El Niño events, while 2002, 2017, and 2020 events did not. This suggests that warmer temperatures caused by the climate crisis are ultimately driving these events. “As summers grow hotter and hotter, we no longer need an El Nino event to trigger mass bleaching at the scale of the Great Barrier Reef,” Hughes said.
"It's now clear that we can have major bleaching events caused by global climate change alone with no tropical forcing," Mark Eakin, coordinator for the National Oceanic and Atmospheric Administration's Coral Reef Watch program, added.
The results also showed that the Great Barrier Reef has suffered its most widespread coral bleaching on record. This is the first time that severe bleaching has affected all three regions of the reef: the northern, central and now large parts of the southern sectors. According to Phys.org, an internet news portal that provides the latest news on science, this is mainly due to the increased global temperature last February, which brought the highest monthly sea temperatures on the Great Barrier Reef since Australia began keeping records in 1900.
But, researchers have anticipated this news. In early March, David Wachenfeld, chief scientist at the Great Barrier Reef Marine Park Authority, reported that the reef was facing a critical period of heat stress over the coming weeks, and that this would be followed by the most widespread coral bleaching the natural wonder has ever endured. Later on, reports show that ocean temperatures across most of the reef were 0.5 to 1.5 degrees Celsius above the March average.
“The forecasts ... indicate that we can expect ongoing levels of thermal stress for at least the next two weeks and maybe three or four weeks. So this still is a critical time for the reef and it is the weather conditions over the next two to four weeks that will determine the final outcome,” Wachenfeld said.
The researchers also found out that the color of the 25% of reefs have disappeared, suggesting that it is severely bleached, with another 35% having recorded modest bleaching. The findings showed that some of the staghorn corals in the south are expected to die in the months ahead, while those that will survive would be less resilient and aren’t likely to make it next time bleaching hits.