No, this island of pumice will not help save the Great Barrier Reef

It's a stunning picture: a raft of pumice the size of a city floating along the Pacific Ocean. But it's not the solution for the dead and dying coral of the world's reefs, as some have suggested.

The only way to save the world's reefs is through mitigating climate change, experts say

This image from the Landsat 8 satellite shows a large island of pumice floating in the Pacific Ocean near Late Island in Tonga on Aug. 13. ( U.S. Geological Survey)

It's a stunning picture: a raft of pumice the size of a city floating along the Pacific Ocean. While some news outlets have hailed it as a possible answer to saving the dead and dying coral of the Great Barrier Reef off the coast of Australia, it's by no means an answer to coral reefs' battle against warming waters as global ocean temperatures rise.

"No," said Mark Eakin, director of Coral Reef Watch, a program that monitors global coral reef systems. "Floating pumice is not going to save the Great Barrier Reef. It's that simple."

Coral is a single animal made up of hundreds to thousands of small creatures called polyps. Microscopic algae live inside the coral's tissue and provide coral with their colour and about 90 per cent of the energy they need to grow.

But these algae, called zooxanthellae, are extremely sensitive to their surrounding water temperature. A difference of even 1 C of warming can cause the algae to leave the coral, leaving behind only the skeleton, what's called a bleaching event. That doesn't mean the coral is dead, but over time, because it is more susceptible to disease, it can die. 

The misguided idea that has been perpetuated by some media outlets is that some of the algal larvae — or other marine life — can latch onto something like pumice and hitch a ride then be deposited onto coral, which could help revive it.

"This floating pumice moving from Tonga to the Great Barrier Reef has been going on for decades," said Eakin, who is also a coral reef specialist with the U.S. National Oceanographic and Atmospheric Administration (NOAA). "We've known about it for decades. So this is nothing new."

Watch and listen as a boat sails through the pumice "raft" in the Pacific Ocean.

While the images are fascinating — and the size of the raft of pumice is impressive — there are a couple of reasons why it won't save or help the Great Barrier Reef in any way.

For one, as Eakin explained, this has been going on for decades and reefs are still facing major die-offs and bleaching events. 

Second, the raft of pumice just doesn't transport enough marine life to make a difference.

"It's not really a good way to bring new recruits in," Eakin said. "It's not going to bring in anywhere near the number of corals that a local spawning event will."

Finally — and definitely the most concerning to marine biologists — is that ocean temperatures are rising with climate change. Parts of the Great Barrier Reef faced major bleaching events in 2016 and 2017 due to unseasonably warm summer ocean temperatures. It's estimated that a 700-kilometre area of the northern region lost an average of 67 per cent of its shallow-water corals in 2016 alone.


James Porter, a professor at the University of Georgia's Odum School of Ecology, said that corals around the world are facing a grim future along our current climate path.

"The two main problems facing the Great Barrier Reef — which are elevated temperatures and lower pH — are not going to be addressed by pumice," Porter said.

A lowering of pH levels in the water, due to warming in the oceans, is causing ocean acidification, which in turn depletes the oceans of the minerals essential to marine life, including corals.

This image from the Australian Research Council's Centre of Excellence illustrates the coral bleaching of 2017 near Orpheus Island in the Great Barrier Reef off the coast of Australia. It was the second year in a row that the reef experienced a major bleaching event. (Greg Torda/ARC Centre of Excellence Coral Reef Studies)

Roughly 93 per cent of all global warming heat is stored in the oceans, Porter noted. 

"The oceans are our punching bag when it comes to climate change," he said. "If the oceans had not absorbed the CO2, the average temperature of Earth would be 122 F [50 C]."

And that's the real problem. With the oceans warming, any algal larvae that reach the coral can't grow because the coral can't provide them with the nutrients they need.

Porter said he worries that this misinformed story about how the island of pumice could help replenish the Great Barrier Reef makes it appear that humans don't have to battle the real issue: climate change.

"I think what happened is that a scientifically interesting story was hyped and blown out of proportion and scale," he said. "It worried me a little when I saw it because I knew it was incorrect."

'Nowhere to run'

The sea surface temperature along the Great Barrier Reef has risen by roughly 0.12 C over the past 30 years. And the Australian government's Great Barrier Reef Marine Park Authority said that, as of 2016, research on corals suggests that the ocean temperature in the reef is "warmer than it has been over the past three centuries.

But when extreme warming events occur during the summer, for example, it can warm the water by 1 C or more.

Though the pumice raft won't be the rescue the Great Barrier Reef needs, it is true that it will transport larvae and other marine life along in its voyage. But in order to save the reefs of the world — and recent data shows another major bleaching event is in its early stages in Hawaii — Eakin and Porter say we need to reduce CO2 emissions and stop the planet from further warming. 

"In order for the pumice transport to work, the stowaway larvae have to be transported to a healthy ocean," Porter said. "But global warming and ocean acidification affect all oceans, so there's nowhere to run."


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at


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