Before the heat wave, the kelps stretched over 800 kilometers of Australia’s western flank and cover 2,200 square kilometers. After the heat wave, Wernberg and Bennett found that 43 percent of these forests disappeared, including almost all the kelps from the most northerly 100 kilometers of the range. “It was just heartbreaking,” says Bennett. “It really brought home to me the impact that climate change can have on these ecosystems, right under our noses.”

“They have provided alarming and detailed evidence for one of the most dramatic climate-driven ecosystem shifts ever recorded,” adds Adriana Verges from the University of New South Wales.

Joan Costa

Indeed, if you think “reef” and “Australia” and you’ll probably picture the Great Barrier Reef—a wonderland of corals off the country’s eastern flank. It’s also experiencing an annus horribilis: a bleaching event that is breaking records and reducing staunch marine scientists to tears and cursing. But while the corals rightly capture attention, far fewer people know about Australia’s other reef—the Great Southern Reef, where kelps, not corals, are king.

The Great Southern Reef envelops the bottom half of Australia in a W-shaped embrace. At 8,000 kilometers, it’s over three times the size of the Great Barrier Reef. It’s also worth more. Recently, Wernberg, Bennett, and their colleagues estimated that it feeds $10 billion dollars into Australia’s economy every year through tourism and fishing. The country’s two most valuable fisheries, for rock lobster and abalone, are critically dependent on kelp, and bring in four times the wealth of all the commercial fishing in the Great Barrier Reef combined. Both are now under threat.

And yet, the kelp reefs are “completely neglected in terms of funding, political, and public awareness,” says Bennett. “Over 70 percent of Australians live adjacent to these things and use them every day, but they’re just not in the public perception.”

Like the corals, the kelp forests host thousands of species, many of which are found nowhere else. Part the wavy fronds and you’ll find a thriving menagerie of crayfish, sponges, crabs, cuttlefish, and colorful fish. Theirs is a three-dimensional world full of layers and hiding places. Since the 2011 heat wave, that high-rise metropolis is gone, replaced by a flattened sprawl. The local flora and fauna have also changed, with the former temperate inhabitants swapped for more tropical species.

Five years later, nothing has changed—a profoundly troubling sign. “The reason we haven’t heard a ton about kelps and climate change in the popular press is because they are the rock stars of marine resilience,” says Jarrett Byrnes from the University of Massachusetts Boston. “Hit them with storms and nutrient-poor water, and within a handful of years they will rebound. Let urchins have at them for decades, and as soon as sea otters come back and remove the urchins, boom, kelp pops back shortly thereafter. If kelps don’t bounce back from a big disturbance after a few years, you know something is deeply wrong.”