Heatwaves Are Destroying Kelp Forests As Well As Coral Reefs

A diver hugs some of the fast vanishing kelp off Western Australia. (C) Joan Costa 2013

Coral reefs are not the only marine ecosystem under threat from hot summers. A study of Western Australia's kelp forests has found nearly half died out during recent extreme summers. Other seaweeds moved in and are proving hard to displace.

North of Perth, the Western Australian coastline is one of the least populated on Earth, and as such free of many of the marine stresses seen in other parts of the world. It is also home to a rich array of ecosystems, including kelp forests that stretch for 800 kilometers (500 miles). At least it was in 2001, when a team began monitoring this coastline. The project gave researchers a rare ringside view of the ways ecosystems change.

“The Indian Ocean adjacent to western Australia is a 'hot spot' where the rate of ocean warming is in the top 10 percent globally,” University of Western Australia's Dr Scott Bennett and co-authors report in Science. Average temperatures at any point are the same as they were 20 to 50 kilometers (12 to 30 miles) north 10 years earlier.

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Researchers explore the kelp forests that survive. (C) Joan Costa 2013

While the slow warming set the stage, it has been the hot summers that leave a legacy. “In December 2010, immediately before an extreme marine heatwave, kelp forests covered over 70 percent of shallow rocky reefs in the midwest,” the paper reports. “By early 2013, only two years later, our extensive surveys found a 43 percent (963 kilometers squared/372 miles squared) loss of kelp forests on the west coast.”

Dividing the coastline into blocks 0.4 degrees of latitude, Bennett found near total extinction of kelp north of 29º, and almost complete survival south of Perth (32º). In between, a little more than half the kelp survived until 2015. Bennett told IFLScience that while most of the world experienced a record hot start to 2016, the Western Australian coast was relatively cool. “There are no signs of recovery but at least the damage was not compounded.”

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