Kelp forests in the Great Southern Reef wiped out by marine heatwave – ‘When we went up to the northern regions and saw that everything was gone, it was devastating’

Desdemona Despair

8 July 2016 (University of Western Australia) – A team of marine scientists led by The University of Western Australia have uncovered the extinction of a kelp forest ecosystem along 100 kilometres of Western Australia’s coastline, following a heatwave that occurred in 2011.

Kelp forests in Western Australia have not experienced a heatwave of this significance before and UWA Associate Professor and lead author Thomas Wernberg from UWA’s Oceans Institute and School of Plant Biology said there were 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 research analysed data collected between 2001 and 2015 along 2,000 kilometres of the Western Australian coastline.

“It shows how the heatwave combined with decades of ocean warming has broken down long-standing biogeographic boundaries with lasting consequences.”

Professor Wernberg said like trees in a forest or corals on a coral reef, the kelp forests were the foundations of the ecosystem.

“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.

“Five years after the heatwave, many cool water fishes, seaweeds and invertebrates have disappeared and been replaced by reef communities from more typical tropical regions.”

Dr Scott Bennett, Research Fellow at the Spanish Research Council and co-lead author of the paper said that tropical grazing fishes had increased substantially in abundance and now prevented kelp forests from recovering.

“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 the likelihood of more heatwaves in the future.”

The extensive loss of kelp forests in Western Australia provides a strong warning of what the future might be like for Australia’s temperate marine environment and the many values it provide to Australians.

The study involved collaboration among CSIRO, AIMS, WA Museum, DPaW, Curtin University, The Australian National University and several international research partners.

A full report of the research can be accessed here.

Contact

Jess Reid (A/UWA Media and Public Relations Manager) (+61 8) 6488 6876 (+61 0) 413 105 200

Kelp forests in the Great Southern Reef wiped out by marine heatwave

ABSTRACT: Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests.

No turning back?

Ecosystems over time have endured much disturbance, yet they tend to remain intact, a characteristic we call resilience. Though many systems have been lost and destroyed, for systems that remain physically intact, there is debate as to whether changing temperatures will result in shifts or collapses. Wernburg, et al. show that extreme warming of a temperate kelp forest off Australia resulted not only in its collapse, but also in a shift in community composition that brought about an increase in herbivorous tropical fishes that prevent the reestablishment of kelp. Thus, many systems may not be resilient to the rapid climate change that we face.

Climate-driven regime shift of a temperate marine ecosystem

By Alice Klein
7 July 2016

Help the kelp. Rising sea temperatures have already wiped out 100 kilometres of kelp forest along the south coast of Western Australia – and this unprecedented loss looks set to worsen.

The Indian Ocean off Western Australia experienced record summer temperatures between 2011 and 2013 caused by a double whammy of global warming and a La Niña weather phase. At their peak, in 2011, sea surface temperatures reached more than 6 °C above average in some areas.

By the end of the heatwave, declines in kelp cover were observed along more than 500 kilometres of the south coast, with complete extinction in the northernmost 100 kilometres.

This rate of kelp loss is the most rapid and extensive ever documented in the world, says Thomas Wernberg at the University of Western Australia in Perth, who led the survey.

“It was quite a shock to come back to these diving locations and all of a sudden realise: ‘Wow – this is completely different’,” he says. “When we went up to the northern regions and saw that everything was gone, it was devastating.” [more]

Biggest ever die-off of ocean forests triggered by warming seas