Australia’s National Coral Bleaching Taskforce has released its first comprehensive map of the Great Barrier Reef’s bleached corals—revealing that a large portion of the reef has been slightly to severely damaged.
Published after extensive dives and flyovers, the map paints a devastating picture of the damage that the Great Barrier Reef—a 2,300-kilometer string of reefs along Australia’s northeast coast—has sustained in recent months.
The bleaching is caused by abnormally hot waters warmed by El Niño and climate change. The temperatures cause corals’ symbiotic algae—their crucial food source—to short-circuit and become toxic, forcing the corals to expel it. Kicking out the algae turns the coral bone white and potentially sets it on a path to starvation.
The Great Barrier Reef is made up of 2,900 smaller reefs. Of the 911 individual reefs that researchers surveyed, a whopping 93 percent—843 reefs—experienced some form of bleaching. What’s more, between 60 to 100 percent of corals were bleached on 316 reefs, many in the remote, pristine northern half of the reef. The Great Barrier Reef’s southern half has mostly avoided severe damage.
Even now, it’s clear that the fallout will be tremendous. The Great Barrier Reef is home to more than 1,500 species of fish, six of the world’s seven marine turtle species, and 30 species of whales and dolphins. What’s more, the UNESCO World Heritage site is a tourism powerhouse, supporting about 70,000 jobs and pumping more than five billion dollars into the Australian economy.
“It’s extremely depressing,” says Mark Eakin of the National Oceanic and Atmospheric Administration’s Coral Reef Watch program. “Having such a large area of the [Great Barrier Reef] affected this severely by bleaching, especially in the northernmost region, where the corals are least affected by local human impact, is very troubling.”
Researchers have yet to finalize the corals’ death tolls, but early estimates suggest that in the northern Great Barrier Reef, about half of the bleached corals are dying. In some areas, the final death toll probably will exceed 90 percent, says Andrew Baird of Australia’s ARC Centre of Excellence for Coral Reef Studies in a press release.
“When bleaching is this severe it affects almost all coral species, including old, slow-growing corals that once lost will take decades or longer to return,” he says.
Most troublingly, the Great Barrier Reef’s current suffering represents a fraction of a much broader regional epidemic: Corals have been bleaching continuously across the Pacific Ocean since mid-2014, as warm waters have assailed reefs from American Samoa to Kiribati and French Polynesia.
The problem, Eakin says, is that climate change has warmed baseline ocean temperatures, which increases the frequency of warming events severe enough to cause bleaching. What’s more, the raised temperatures make El Niño warming events—even those too weak to be designated official El Niños—all the more dangerous.
“By the middle of the 21st century, we’re going to be seeing mild bleaching on most reefs around the world,” says Eakin. “If it takes decades for reefs to recover even under the best conditions, and bleaching events become more and more frequent, it doesn’t necessarily give reefs time to recover.”
And if carbon emissions continue unabated, Eakin warns, temperatures will continue to rise, threatening coral reefs worldwide with increasingly intense, frequent bleaching.
Eakin notes, however, that the UN’s ambitious Paris Agreement could help, if it were immediately and boldly implemented. The international pact calls for containing global warming to 1.5 degrees Celsius above pre-industrial averages, a threshold that could save at least some of the world’s corals from a bleak, bleached future.
“We really need to limit warming to 1.5 degrees or less,” Eakin says. “Coral reefs don’t stand much of a chance on the trajectory we’re currently on.”