Recovery of Corals on Great Barrier Reef Pauses Due to Bleaching and Disease
A recovery in the number of corals growing on the Great Barrier Reef over recent years has come to a standstill, as government scientists blame bleaching, disease, and attacks by starfish. Results from the latest annual surveys of more than 100 individual reefs show a small drop in coral cover over the northern and central parts of the reef over the past year.
The Great Barrier Reef, the world’s biggest coral reef system, faces an uncertain future as the ocean continues to accumulate heat caused by the burning of fossil fuels. The heat has caused a series of mass coral bleaching events over the reef, including four in the past seven years, that can weaken corals and affect their ability to reproduce.
The report from the Australian Institute of Marine Science details the results of in-water surveys of 111 reefs carried out between August 2022 and May this year. The surveys came after the summer of 2022, which saw the first mass coral bleaching on record to occur during a La Niña – a climate pattern that usually brings cooler conditions.
According to the report, “The effects from the 2022 bleaching event, the fourth in seven years, caused some coral loss on some reefs. It is likely that those corals which survived bleaching have been affected by reduced growth and reproduction.” Last year’s report mentioned three years of relatively benign conditions that produced record levels of coral cover in the reef’s northern and central areas. However, the recent data suggests a pause in coral growth.
Dr. Mike Emslie, who leads the long-term reef monitoring program at Aims, expressed surprise at the data, stating, “This demonstrates that even less-severe bleaching events are enough to cause a pause in coral cover.” He also highlighted the continued risks faced by the reef, including the possibility of another mass bleaching event, as well as the threats posed by crown-of-thorns starfish and coral disease.
When corals are exposed to unusually warm water for prolonged periods, they separate from algae that live inside them. The algae provide nutrients to the corals and give them their vibrant colors. Although corals can recover if temperatures are not too extreme, scientists warn that there are also “sub-lethal” effects from bleaching.
Reef experts are concerned that an El Niño climate pattern could take hold this summer, further raising the risk of another mass bleaching event. Dr. David Wachenfeld, the research program director at Aims, emphasized the precarious state of the reef, saying, “However, we are only one large-scale disturbance away from a rapid reversal of recent recovery.”
The report indicated that hard coral cover in the northern section of the reef, from Cape York to Cooktown, was estimated at 35.7%, down from 36.5% in 2022. In the reef’s central region, between Cooktown and Proserpine, coral cover was estimated at 30.8%, down from 32.6% last year. In the southern region, from Proserpine to Gladstone, coral cover was at 33.8%, virtually unchanged from the previous year, although some reefs in this section were affected by disease and crown-of-thorns starfish attacks.
The future of the Great Barrier Reef hangs in the balance as it grapples with the impacts of climate change and other threats. As scientists continue to monitor and assess the situation, urgent action and concerted efforts are needed to protect and preserve this natural wonder for future generations.