‘Extreme Marine Heat Wave’ Wipes Out an Entire Underwater Forest in Australias’s Great Southern Reef

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This year, the tragic die-off of large volumes of coral at the treasured Great Barrier Reef has provided a climate change shock like few others. The cause was too much warm water – which seems to have pushed the corals past a thermal survival threshold. And that warm water, in turn, is tied to climate change.

Now, however, a team of researchers has revealed that another Australian coastal ecosystem that gets less attention – Australia’s kelp-dominated Great Southern Reef, which covers a huge expanse along its more temperate southern and southwestern coast – saw an equally dramatic ecosystem upheaval five years ago. And the cause was the same – what the scientists call an “extreme marine heat wave.”

“Some of the same types of drivers are behind all of this, and I think this really emphasizes the manifestation of these climate-driven events. It’s more than just the coral reefs that are being affected by this,” says Thomas Wernberg, a marine biologist at the University of Southern Australia who led the new research, which appeared Thursday in the journal Science. Wernberg conducted the research with 21 other authors from a variety of institutions in Australia and abroad.

Many Americans will be familiar with the towering kelp forests off the coast of California, where these enormous organisms can grow to be more than 30 metres tall. The kelp off Australia’s southern and southwestern coasts aren’t nearly as tall, but they are still the backbone of a rich ecosystem, and the researchers still refer to the organisms as creating a “kelp forest.” Wernberg and his colleagues estimate the Southern Reef as a whole to be worth $13 billion each year in economic terms because of tourism, fisheries and other benefits.

But in 2011, a surge of ocean temperatures between 3 and 5 degrees Celsius above normal – conditions that for the kelp represented “the hottest in recorded history, and that’s going back 215 years,” Wernberg says – took a devastating toll on a major part of this ecosystem.

In the most northern (in the southern hemisphere, the warmest) latitudes, along the southwest coast of Australia south of Kalbarri, kelp forests died off in dramatic numbers, suggesting the temperatures had “exceeded a physiological tipping point for kelp forests,” the study reports.

“When the heat wave happened, all of those northern kelp forests were basically wiped out in a couple of months,” Wernberg says. “And southwards, at least a couple hundred kilometers, there were quite substantial impacts, but you gradually got more and more kelps as you went further south.”

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SOURCE: National Post; The Washington Post, Chris Mooney