- Both aerial and in-water surveys have shown that the southern section of the Great Barrier Reef is undergoing extensive coral bleaching.
- Surveys have also shown “limited bleaching” in the northern part of the Great Barrier Reef.
- However, scientists and reef managers plan to conduct more air and in-water surveys to further assess the coral bleaching across all parts of the Great Barrier Reef.
- Scientists suspect but have not yet confirmed that a seventh mass bleaching event since 1998 is currently underway; the last mass bleaching event on the Great Barrier Reef happened in 2022.
The southern section of the Great Barrier Reef is undergoing extensive coral bleaching, according to researchers who recently surveyed the region. The discovery has raised fears that this fragile coral reef system is on the brink of a seventh mass bleaching event since 1998.
In late February, scientists from the Australian Institute of Marine Science (AIMS), a tropical marine research center in Townsville, Queensland, and staff from the Great Barrier Reef Marine Park Authority (also known as the Reef Authority), the federal agency that manages the reef, conducted a series of helicopter surveys to assess the health of dozens of reefs along the southern region of the Great Barrier Reef.
The surveyed reefs included 27 inshore reefs of the Keppel Islands and the Gladstone region and 27 offshore reefs in what’s known as the Capricorn Bunker group.
The Reef Authority reported that coral bleaching was “extensive and fairly uniform” across all surveyed reefs and aligned with observations of accumulated heat stress.
“In the reef communities surveyed most coral cover displayed some level of bleaching with white and fluorescent colonies observed in shallow reef areas,” Mark Read, the director of reef health at the Reef Authority, said in a statement.
Neal Cantin, a senior research scientist at AIMS, said the team also observed “limited bleaching” further north, affecting coral reefs above the city of Mackay and even into the Whitsunday Islands, during additional surveys.
Cantin also said that calm conditions in the region provided good visibility, and that the team had observed “bleached corals at depth quite clearly across the reef slope from the air.” However, he added that further in-water surveys will be needed to better assess the extent of the bleaching.
Researchers from James Cook University’s Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) have already conducted some in-water surveys around the Keppel Islands as part of a separate study process, and they reported moderate to severe coral bleaching in the southern section of the Great Barrier Reef.
“I have been working on these reefs for nearly 20 years and I have never felt the water as warm as this,” Maya Srinivasan, a scientist at TropWATER, said in a statement.
“Once we were in the water, we could instantly see parts of the reef that were completely white from severe bleaching,” Srinivasan added. “Some corals were already dying.”
In the coming weeks, scientists and reef managers plan to conduct further air and in-water surveys to assess the coral bleaching across all parts of the Great Barrier Reef, including the northern section.
The Great Barrier Reef is the world’s largest coral reef, extending across 348,000 square kilometers (134,000 square miles) and comprising nearly 3,000 individual reefs. The reef system is a biodiversity hotspot, providing a home to about 1,500 fish, 400 coral, 4,000 mollusk and 240 bird species, as well as a diversity of sponges, anemones, marine worms, crustaceans, and other species. Dozens of marine mammals can also be found along the Great Barrier Reef, from humpback whales to dugongs to bottlenose dolphins.
Yet this region has been experiencing frequent marine heat waves brought on by human-induced climate change. Heightened sea temperatures have then led to widespread coral bleaching. This happens when heat-stressed coral expels life-sustaining algae from its tissues, effectively starving the coral. Some corals can recover from coral bleaching, but if heat stress continues for too long, the corals will eventually die.
The Great Barrier Reef system has experienced six previous mass bleaching events: in 1998, 2002, 2016, 2017, 2020, and 2022. Scientists suspect but have not yet confirmed that a seventh mass bleaching event is currently underway.
While these mass bleaching events have been detrimental to the Great Barrier Reef, monitoring efforts have shown that some coral and fish communities have been able to recover.
“We have seen fish abundance decline as coral cover declines in this region following past impacts like this,” Srinivasan said. “But we have also seen the recovery of coral and fish communities on many areas of reef — there just needs to be enough time between impacts to allow this recovery to occur.”
Banner image caption: Coral bleaching in the Great Barrier Reef in 2017. Image by The Ocean Agency / Ocean Image Bank.
Elizabeth Claire Alberts is a senior staff writer for Mongabay’s Ocean Desk. Follow her on Mastodon, @ECAlberts@journa.host, Blue Sky, @elizabethalberts.bsky.social, and Twitter @ECAlberts.
https://news.mongabay.com/2023/10/will-we-lose-most-of-the-great-barrier-reef-by-february/