Climate Change: Tropical Heatwave Wipes Out Ocean Forests Off WA

The Australian - Victoria Laurie

Rocky reefs in Kalbarri in 2005, and in 2013 after a heatwave wiped out extensive underwater forests of kelp. Picture: T. Wernberg

Kelp forests off the coast of Western Australia have been wiped out by a heatwave, providing a strong warning of what the future might be like for Australia's temperate marine environment.
A team of marine scientists led by The University of Western Australia uncovered the extinction along 100km of Western ­Australia's coastline following a heatwave in 2011.
Kelp forests in the state's southern coastal waters, which contain huge diversity in seaweed species, have not experienced a heatwave of this significance ­before.
Lead author Thomas Wernberg from the UWA's Oceans Insti­tute and School of Plant ­Biology said the heatwave had ­followed decades of ocean warming, and the kelp forest showed no signs of recovery five years later.
"Temperatures exceeded anything previously experienced by these kelp forests and they collapsed, allowing turf algae, tropical and subtropical fish, seaweed and coral to increase rapidly," Professor Wernberg said.
The appearance of turf seaweeds and grazing fishes now prevented the return of kelp forests, he said, leading to a fundamental change in the coastal ecosystem. "Five years after the heatwave, many cool water fishes, seaweeds and invertebrates have disappeared and been replaced by reef communities from more typical tropical regions."
Professor Wernberg said the kelp forests were a key element of the ecosystem, like trees in a forest or corals on a coral reef.
"Kelp forests are the biological engine of Australia's Great Southern Reef, where they support ­globally unique temperate marine biodiversity, some of the most valuable fisheries in Australia and reef-related tourism worth over $10 billion per year," he said.
Co-lead author Dr Scott ­Bennett, from the Spanish ­Research Council, said tropical grazing fish were seen only rarely in the region before the heatwave, but had proliferated.
"The impact has been particularly prominent at northern reefs, where kelp forests have disappeared completely," he said.
"Recovery is unlikely because of the large grazing pressure, continued warming and like­lihood of more heatwaves in the future."
The research team, including scientists from CSIRO, WA Museum and overseas ­researchers, analysed data collected between 2001 and 2015 along 2000km of the West Australian coast.

Links

• Forests of the sea in Western Australia slashed by marine heatwave
• Massive kelp forests off Western Australia have been destroyed in a marine heatwave
• A marine heatwave has wiped out a swathe of WA's undersea kelp forest
• Australia's vast kelp forests devastated by marine heatwave, study reveals