Over the past 25 years, the Great Barrier Reef coral has more than halved. Marine biologists from the ARC Centre of Excellence for Coral Reef Studies have been tracking the coral communities and their size since 1995. They assessed the data between then and 2017 and found the number of coral (small, medium, and large) fell over 50%. The study has prompted scientists to warn the world yet again that the famous landmark will soon become unrecognizable if we fail to reduce greenhouse gas emissions immediately.
The study’s co-author, Terry Hughes, a James Cook University professor, and marine biologist, said:
There’s not much time to lose. I think if we can control warming somewhere between 1.5-2C [above pre-industrial levels], as per the Paris agreement, then we’ll still have a reef. But if we get to 3-4C because of unrestrained emissions, then we won’t have a recognizable Great Barrier Reef.
We used to think the Great Barrier Reef is protected by its sheer size, but our results show that even the world’s largest and relatively well-protected reef system is increasingly compromised and in decline.
The researchers found that the four mass bleaching events had the most significant impact on coral depletion. Record-breaking water temperatures trigger bleaching events. The research didn’t even consider the severe bleaching event that happened earlier this year, meaning the coral reduction may be more than estimated. During the study period, the reef also experienced several local cyclones and two significant outbreaks of the crown-of-thorns starfish.
Hughes said:
I began surveying the reefs in 1995, and what subsequently unfolded certainly wasn’t planned for. There have been five major bleaching events since then, including three in just the past five years. I am very concerned about the shrinking gap between bleaching events.
The research covered all 2,300 kilometers (1,429 miles) of the Great Barrier Reef and found loss at every level. This is dangerous because looing older coral could have a cascading effect on the entire reef system.
Hughes continued:
While small, medium, and large corals had each been depleted, the decline in larger corals was the greatest threat to the reef’s ability to repair as they spawn more babies. The loss of medium and large colonies is particularly worrisome, as they could possibly stunt reproduction and stop older corals from replenishing shrinking populations. At the same time, the disproportionate loss in smaller colonies suggests a reduction in tiny coral larvae being spread about.
The species of corals to have suffered the most significant decline were staghorn corals, also known as branching corals, and table corals. Those two types of corals are the most three-dimensional – they form habitats. The loss of habitat affected fish numbers and the productivity of coral reef fisheries. The reef is flatter and less three dimensional now.
To make matters worse, the window for recovery is getting narrow. The more frequent the bleaching events are, the harder it is for the reef to rebound. Eventually, it won’t be able to recover at all. If emissions aren’t cut by the end of the century, bleaching events will likely occur annually.
Andy Dietzel, a researcher from the ARC Centre of Excellence for Coral Reef Studies, added:
A vibrant coral population has millions of small, baby corals, as well as many large ones – the big mamas who produce most of the larvae. Our results show the ability of the Great Barrier Reef to recover – its resilience – is compromised compared to the past, because there are fewer babies, and fewer large breeding adults.
In 2019, the Great Barrier Reef Marine Park Authority downgraded the reef system’s outlook in its five-yearly reef health report to “very poor.” It warned that the climate crisis is the single greatest challenge facing the reef system. Escalating atmospheric greenhouse gases causes global heating, which is a significant threat to all coral reef ecosystems worldwide. The only way to preserve them is by reducing emissions.
