A marine heatwave has wiped out a swathe of WA’s undersea kelp forest

Scott Bennett, Curtin University; Julia Santana-Garcon, and Thomas Wernberg, University of Western Australia

Kelp forests along some 100km of Western Australia’s coast have been wiped out, and many more areas damaged, by a marine heatwave that struck the area in 2011.

The heatwave, which featured ocean temperatures more than 2℃ above normal and persisted for more than 10 weeks, ushered in an abrupt change in marine plant life along a section of Australia’s Great Southern Reef, with kelp disappearing to be replaced by tropical species.

As we and our international colleagues report in the journal Science, five years on from the heatwave, these kelp forests show no signs of recovery.

Instead, fish, seaweed and invertebrate communities from these formerly temperate kelp forests are being replaced by subtropical and tropical reef communities. Tropical fish species are now intensely grazing the reef, preventing the kelp forests from recovering.

Kelp forest before (left) and after (right) the marine heatwave.
Author provided

Assessing the damage

We and our team surveyed reefs along 2,000km of coastline from Cape Leeuwin, south of Perth, to Ningaloo Reef between 2001 and 2015.

Up until 2011, temperate reefs were clearly defined by the distribution of kelp forests which formed dense, highly productive forests as far north as Kalbarri in WA’s Mid West.

Since 2011, the boundary between these temperate reefs of southern WA and the more tropical reefs (including Ningaloo) to the north has become less clear-cut. Instead, the sharp divide has been replaced by an intermediate region of turf-dominated reefs.

Infographic illustrating the impacts of the heatwave, kelp loss and tropicalisation of temperate reefs.
[Produced by Awaroo]((www.awaroo.com))

This has implications for the Great Southern Reef (GSR), which extends more than 8,000km around the southern half of Australia from the southern half of WA all the way to southern Queensland – a coastline that is home to around 70% of Australians.

Kelp forests are the GSR’s “biological engine”, feeding a globally unique collection of temperate marine species, not to mention supporting some of the most valuable fisheries in Australia and underpinning reef tourism worth more than A$10 billion a year.

But our research shows that on the GSR’s western side, kelp forests are being pushed towards Australia’s southern edge, where continued warming puts them at risk of losses across thousands of kilometres of coastline because there is no more southerly habitat to which they can retreat.

While the 2011 marine heatwave affected some 1,000km of Western Australia’s temperate coastline, it was a stretch of roughly 100km extending south of Kalbarri on the state’s Mid West coast that was most severely affected.

In this area alone an estimated 385 square km of kelp forest have been completely wiped out.

Further south, from Geraldton to Cape Leeuwin, the extent of kelp loss was less severe, despite an estimated total area of 960 square km having been lost in the region.

Northern regions towards Kalbarri were more severely affected because these kelp forests were closer to their limit, and also because this area is closer to the tropical regions like Ningaloo Reef, meaning that tropical species could more easily move in.

A school of tropical rabbitfish moves through the affected area.
Thomas Wernberg, Author provided

The problem was exacerbated by the southward-flowing Leeuwin Current, which helps tropical species move south while making it harder for temperate species to move north and recolonise the affected areas of the GSR.

The combination of these physical and ecological processes set within a background warming rate roughly twice the global average, compounds the challenges faced by kelp forests in the region.

The plight of WA’s kelp forests provides a strong warning of what the future might hold for Australia’s temperate marine environment, and the many services it provides to Australians.

The Conversation

Scott Bennett, Marie Curie Fellow at the Spanish National Research Council (CSIC), Curtin University; Julia Santana-Garcon, Postdoctoral research associate in Marine Ecology, and Thomas Wernberg, ARC Future Fellow in Marine Ecology, University of Western Australia

This article was originally published on The Conversation. Read the original article.


Why Antarctica depends on Australia and China’s alliance

Nengye Liu, University of New England

Antarctica’s early history was marked by national rivalries – think of Britain and Norway racing to the South Pole in 1911. But since the signing of the Antarctic Treaty in 1959, collaboration has become more important than competition. And the relationship between Australia – Antarctica’s biggest territorial claimant – and China, the emerging superpower, is among the most crucial of all.

One of Australia’s key aims, as set out in its Antarctic Strategy and 20 Year Action Plan, is to strengthen the existing Antarctic Treaty system, by “building and maintaining strong and effective relationships with other Antarctic Treaty nations through international engagement”.

As Australia’s largest trading partner and a significant player in Antarctica, China is a crucial nation with which to engage if Australia is to meet its objectives. This raises the question of how the two countries might fruitfully cooperate in Antarctica over the next 20 years.

Existing ties

China began its first scientific expedition to Antarctica in 1984. It now has four Antarctic bases, two on Australian-claimed territory.

Australia and China’s Antarctic ties have thus been evolving for more than three decades, with a focus on science, logistics and operations. Bilateral relations seem to have strengthened in recent years.

In 2014, President Xi Jinping visited Hobart and signed a memorandum of understanding with Australia to collaborate in Antarctica and the Southern Ocean.

Last year, Australia’s Antarctic Climate and Ecosystems Cooperative Research Centre signed an agreement with its Chinese counterpart, the National Marine Environmental Forecasting Centre, to develop new forecasting methods to aid the challenging task of navigating Antarctic sea ice.

February 2016 saw the inaugural meeting of the China-Australia Joint Committee on Antarctic and Southern Ocean Collaboration, which arose from the 2014 agreement.

But it has not all been smooth sailing. China has strongly opposed Australia’s proposal to establish a network of marine protected areas off East Antarctica.

Proposed marine parks off East Antarctica.
Australian Antarctic Division

Australia is also concerned about China’s presence in Antarctica. For example, a news article at the time of Xi’s 2014 visit suggested that “China may eventually try to overthrow the Antarctic Treaty system underpinning Australia’s claim to 43% of the frozen continent”, while questions have been asked about the scope of China’s mining ambitions on the frozen continent.

Potential future collaborations

There are several reasons, however, to expect that China and Australia can put aside their diplomatic differences in pursuit of Antarctic science.

First, it seems more likely that China will continue to endorse the Antarctic Treaty than to undermine it. As a rising power, China has growing interests in the Southern Ocean but it has no territorial claim in Antarctica. It would certainly not be at the front of the queue in the ensuing land grab if the treaty were to end.

Realistically, China should therefore continue to support the treaty, under which the seven existing national claims (plus any prospective claim by the United States, which has a research base at the South Pole) are suspended.

This logic is backed up by China’s behaviour with regard to the even more politically fraught North Pole. By becoming an observer of the Arctic Council, China has opted to embrace rather than challenge the current Arctic regime, despite the jockeying among Arctic nations over territorial rights.

Second, to maintain Australia’s leadership and excellence in Antarctic science, it will need to collaborate with industry and other nations. As an economic powerhouse, China has both the funding and the technology to deliver things like icebreaker ships, a well as a keen interest in Antarctica, which should extend to long-term scientific collaborations.

Third, Australia wants to maintain its leadership in environmental stewardship of Antarctica. One current hurdle seems to be China’s opposition to Australia, France and the European Union over the planned marine protected areas off East Antarctica. As the world’s largest fishing nation, China’s reluctance to support “no-take zones” is hardly surprising.

Nevertheless, this issue could potentially be converted from obstacle to opportunity, perhaps by Australia inviting Chinese scientists to conduct joint scientific research in these areas of the Southern Ocean. This would not only improve understanding of unknown marine ecosystems, but would also be a useful way for Australia to exert diplomatic “soft power”.

Antarctica is increasingly attractive to the more affluent of China’s tourists.
Butterfly voyages/Wikimedia Commons, CC BY-SA

Finally, Australia has its own economic interests in Antarctica, such as sustainable fishing and tourism. Meanwhile, ever greater numbers of Chinese tourists are venturing abroad, with visits to Australia passing the 1 million mark last year. With Antarctica now also on the radar for China’s richer tourists, Australia could not only benefit economically but must also work closely with China to develop regulations that prevent this nascent industry from damaging the Antarctic environment.

All of this means we can reasonably expect Australian-Chinese ties to grow ever closer over the next two decades – even in the world’s remotest place.

This article is part of a series on Australian science and diplomacy in Antarctica. Look out for more articles in the coming days.

The Conversation

Nengye Liu, Senior Lecturer in Law, University of New England

This article was originally published on The Conversation. Read the original article.