The amount of coral has increased in the northern and central parts of Australia‘s Great Barrier Reef. In the 36 years that the Australian Institute of Marine Sciences has been researching the state of the reef annually, coral cover there has never been higher. Nevertheless, the researchers are afraid that this positive development due to climate change is only short-lived.
In the southern part of the reef, coral cover decreased slightly last year, due to the presence of crowns of thorns. These starfish eat the coral.
According to the research report, the reef has been able to grow in the northern and central parts because, in the past twelve months, there have been relatively good living conditions for the coral polyps, the small critters that make up the coral. For example, there were few devastating cyclones in the area, and also fewer crowns of thorns than in previous years.
Lead researcher Mike Emslie tells Reuters news agency that it “has shown coral to be strong and resilient enough to recover when there are no disruptions”. Still, he warns for the future: “The higher ocean temperatures cause stress to the coral and can lead to large-scale bleaching.”
Coral bleaching occurs when the water temperature becomes too high for the algae that live in the coral’s tissue. These plants convert sunlight into important nutrients for the coral. Without these nutrients, the coral tissue becomes transparent and the coral‘s white calcareous skeleton becomes visible.
Swipe to see the difference between healthy and bleached coral:
This process is dangerous, because the coral can die if the algae and color stay away for too long. The last bleaching was in March. It was exceptional at the time that this happened during the climatic phenomenon of La Niña, a period when the oceans are usually cooler.
According to the researchers, this shows that the sea temperature is rising and large-scale bleaching will occur more and more frequently. Due to the favorable conditions, the coral was able to recover quickly this time, but this does not happen every time. In 2017 and 2018, for example, large parts of the Great Barrier Reef died after bleaching.
According to the researchers, the rapid recovery of the reef is mainly due to Acropora corals. This species is growing rapidly and is now the most common in the Great Barrier Reef. But Acropora are also more prone to bleaching than other species.
The investigation report therefore ends with a warning. “Our predictions for the future point to increasing and prolonged marine heat waves, as well as an ongoing risk of tropical cyclones and thorn-crown star outbreaks.”
The researchers call their finds good news for the current state of the reef, but are afraid it won’t last long.