Reportage

A subantarctic sentinel

Solving the mystery of Macquarie Island’s dieback

IN A BACK corner of the Royal Tasmanian Botanical Gardens in Hobart is an unassuming but very special teardrop-­shaped pale-­yellow building. Made of thick concrete and roughly fourteen metres long by six metres wide, it is reminiscent of a small wartime bomb shelter. Grey rocks and grasses line its base and above its double-­layer clear polycarbonate roof is a white metal frame that supports a large sunshade. Beside the glass entrance door is a sign inviting visitors to ‘come inside and step ashore on a subantarctic island’.

The subantarctic region, located a few degrees of latitude either side of the Antarctic Convergence, mightn’t have the same mythical status – the same hold on the collective human imagination – as the icy continent further south does, but it does contain numerous islands that are havens of life in the middle of the huge oceanic desert that is the Southern Ocean. The Subantarctic Plant House, as this building is known, is modelled on one of these islands: Macquarie Island, a cold, wet and windy speck of land located halfway between Tasmania and Antarctica.

The carefully controlled environment inside the Subantarctic Plant House attempts to re-­create the one on Macquarie Island – or ‘Macca’, as it is more affectionately known. It is grey and dim. Freezing air blasts out of four vents beside the door and occasionally a cool mist blows around the room. Covering the wall is a hand-­painted mural featuring scenes from the island: petrels nesting on cliff faces, king penguins waddling across a shingle beach pounded by huge waves, and rain pouring down onto a cloud-­shrouded plateau. The stream that trickles through a patch of mire into a small pool and the field recordings of grunting and bellowing elephant seals playing from speakers make it even easier to imagine that you have indeed suddenly stepped ashore on Macca.

As does the collection of beautiful plants – the lush green ferns, megaherbs, mosses, grasses and liverworts. Situated on either side of a small wooden boardwalk that leads around the room, they – along with the rocks and gravel they are growing in, over and between – were all collected from Macquarie Island in the 1990s. Having evolved in such a harsh environment, none of them are particularly large; among the biggest is Stilbocarpa polaris, a megaherb commonly known as Macquarie Island cabbage that reaches only a metre in height and whose saucer-­sized, leathery leaves are covered in fine white hairs – just like the thin stems they grow on – that help trap heat.

But the Subantarctic Plant House isn’t a complete microcosm of the flora on Macquarie Island. One plant that is missing is the endemic Azorella macquariensis. Once confused with the closely related Azorella selago found on other subantarctic islands, it is a very slow-­growing and very compact semi-­deciduous cushion plant with diminutive flowers that lives in just the top two centimetres of soil and depends on a consistently wet and misty environment to thrive. In many parts of Macquarie Island, it forms giant, iridescent-­green terraces and undulating carpets that can be hundreds of years old and collect significant amounts of carbon, prevent erosion and support a diverse range of epiphytes and microarthropods. Because of this, the plant is considered a keystone species – an ecosystem engineer – just as eucalypts are in so many forests throughout the Australian continent.

There was a brief period when the Royal Tasmanian Botanical Gardens did have one specimen of Azorella macquariensis in its subantarctic collection. But – as Lorraine Perrins, curator of the Conservation Collections and Subantarctic Flora at the gardens explains – mimicking the exact environmental conditions found on Macquarie Island is ‘practically impossible’ and as a result the plant ‘struggled’; it was very etiolated and did not form the tight canopy that characterises the species. Then, in 2011, the cooling system of the Subantarctic Plant House broke down and was disabled for several weeks. Despite their best efforts, Perrins and her colleagues could not save the already-­struggling Azorella macquariensis specimen. Its death, Perrins says, was ‘devastating’.

It was also symbolic of a far more devastating and ongoing rapid mass-­mortality event affecting the entire population of Azorella macquariensis on Macquarie Island. Although much mystery still surrounds the widespread dieback of the cushion plant and the associated ecosystem collapse, scientists know enough about it already to confidently say it is further proof that nowhere, no matter how protected or free of other environmental pressures, is safe from catastrophic climate change – and to fear for the future of other subantarctic islands and the rare and beautiful life forms that live on them.

 

THE DIEBACK OF Azorella macquariensis is another tragic chapter in Macquarie Island’s extraordinary history.

Roughly thirty million years ago and 4,000 metres below sea level, the Indo-Australian and Pacific tectonic plates started to tear apart. Molten rock surged through the rift between them and solidified as it cooled, forming a new oceanic crust. Over time the two plates started to crash together, creating a ridge in the crust that gradually rose through the lightless depths until, approximately 600,000 years ago, its crest broke through the waves.

Since that moment, the piece of raised oceanic crust that is Macquarie Island has continued to be uplifted at a rate of several millimetres per year; characterised by an undulating alpine plateau dotted with lakes that sits atop steep scarps, its highest point is presently 435 metres above sea level. Although it is only thirty-four kilometres long and 5.5 kilometres wide, the vast submarine mountain range of which it’s the subaerial tip stretches 1,600 kilometres from the South Island of New Zealand to near the Antarctic continent. Known as the Macquarie Ridge, it is significantly steeper than the Himalayas, the Andes and all of the world’s other great terrestrial mountain ranges.

Being the only known place where rocks from the Earth’s mantle, six kilometres below the ocean floor, are being actively exposed above sea level – and that contains a complete and distinct sequence of rocks from the upper mantle to the upper crust – Macquarie Island is invaluable to understanding the geological features and processes of oceanic crust formation and plate boundary dynamics. Indeed, its unique geomorphology was one of the main reasons why, in 1997, UNESCO agreed that it had outstanding universal value and inscribed it on the World Heritage list.

Another was the array of flora and fauna it supports. Despite its small size, Macquarie Island is home to nearly fifty vascular plant species as well as eighty-­six species of mosses and fifty-­one species of liverworts – all of which arrived via long-­distance dispersal on the wind or on the wings of birds. It also provides critical feeding and breeding grounds for a plethora of wildlife, including 100,000 seals and four species of penguins totalling four million birds that form vast colonies on its shingle beaches and tussocky coastal platform and slopes.

Since the ageing research station on the isthmus was built in 1948, Macquarie Island has been used as a base for globally significant scientific research. But earlier human visitors to the island used it for a very different reason.

One of the earliest human visitors was Frederick Hasselborough, who was captaining the Perseverance on a voyage to sealing grounds south of New Zealand in July 1810 when it was blown off course. While the charted course was lost, Hasselborough spotted an island in the distance. Although evidence was later found indicating Polynesian sailors had previously visited this island, Hasselborough believed it was undiscovered and took the liberty of naming it in honour of the then Governor of New South Wales, Lachlan Macquarie.

Upon seeing that the island’s shores were teeming with fur seals, Hasselborough put a small gang of men ashore to begin harvesting their pelts while he sailed north to Sydney for extra provisions, determined to keep secret what he had found. He succeeded in doing so until – as the tale goes – the evening before he returned to Macquarie Island, when he attended a farewell party that had been organised by a merchant and sealing master named Joseph Underwood.

Unbeknown to Hasselborough, the party was part of Underwood’s plan to try to dupe him into revealing the location of his recent discovery. When it was in full swing, Underwood proclaimed that he had known about the island for several years and bet Hasselborough £20 that he could name its precise position. Too drunk on rum and his own ego to realise he was being hoodwinked, Hasselborough accepted the challenge and doubled the stakes before writing in chalk on the underside of the table – as had been agreed – the island’s exact co-ordinates: 55ºS, 159½ºE. Underwood then took the chalk and, pretending to stoop down to write his entry in the competition, simply looked at the figures Hasselborough had written. He feigned disappointment, crying out ‘I have lost’, but he knew the knowledge he had just gained was worth significantly more than the money he gladly handed over to Hasselborough.

It didn’t take long for this knowledge to spread wider – and for Macquarie Island to become an open-­air slaughterhouse. By December 1810, another three Sydney-­based sealing gangs were operating there and, within the first eighteen months of operation, roughly 120,000 fur seals had been killed for their fine pelts. Within a decade, fur seals were effectively wiped out on the island and sealing gangs then turned their clubs on the elephant seals and, later, penguins, the blubber of which was stripped and boiled down for the oil it contained, then shipped around the world to illuminate houses and entire cities.

In 1920, following a sustained environmental campaign led by Sir Douglas Mawson and other members of the Australian Antarctic Expedition who established the first major scientific base on Macquarie Island in 1911, the commercial exploitation of its wildlife finally ceased. Thirteen years later, it was formally declared a wildlife sanctuary, and the seal and penguin populations slowly started to recover. But the sealers left behind not just their huge rusting try pots, digesters and boilers but also a destructive environmental legacy in the form of numerous invasive species, such as mice, rats, cats, wekas and rabbits, which voraciously preyed on seabird chicks and eggs and stripped entire coastal slopes of native vegetation. This led to significant erosion and loss of nesting habitat long after the last penguins and seals had been clubbed to death.

Efforts to eradicate the huge number of invasive animals on Macquarie Island began in earnest in the mid-­twentieth century. Cats were finally eradicated from the island in 2000 following a fifteen-­year program (although not before they had helped drive two native birds – the Macquarie Island parakeet and the Macquarie Island rail – to extinction). But this had the unintended consequence of causing rabbits to dramatically multiply, as they were no longer preyed upon, prompting the establishment in 2007 of a new $25 million project to simultaneously eradicate rabbits, mice and rats from the island using a combination of baits, skilled hunters and specially trained dogs. Seven years later, the project was declared a success, making it the largest successful island pest-­eradication program ever attempted.

This was a major cause for celebration among the scientists working on the island. But by then they had a fresh cause for major concern: the widespread dieback of Azorella macquariensis.

 

AS WHEN FREDERICK Hasselborough stumbled upon Macquarie Island, Dr Dana Bergstrom discovered the dieback of Azorella macquariensis by chance.

An award-­winning applied ecologist with the Australian Antarctic Division, Bergstrom has soft blue eyes, curly salt-­and-­pepper hair, and a vast knowledge of the Antarctic and subantarctic regions that she’s gained over the nearly three decades she’s spent researching them. She first visited Macquarie Island – ‘a little jewel in the ocean’ – as a twenty-­one-­year-­old master’s student in 1983 to research fossil peats. The trip was challenging – she didn’t have proper boots, a proper raincoat and suffered hypothermia – but it left a deep and lasting impression on her.

‘I fell in love with the place then,’ she says. ‘It got into my blood.’

On many subsequent research trips to Macquarie Island, Bergstrom became very familiar with Azorella macquariensis. To her, it is one of the most bizarre plants on the planet – ‘like a whole bunch of balloons blown up with water and sandwiched together’ – and one of the most beautiful. She likens the vast terraces and carpets it forms over the landscape to ‘old-­growth forests’.

One specimen of Azorella macquariensis Bergstrom became particularly familiar with was located on the northern end of the island, near the beginning of the descent from the plateau to the research station. Shaped like the island itself, it always gave her joy whenever she spotted it on her way back from being out in the field. ‘No matter how bad the weather was, you’d see it and think, “I’m almost there.” It was a little signpost, which is helpful because sometimes you can’t see ten metres because of the fog and the mist.’

In December 2008, Bergstrom was on the island mapping vegetation when she saw that this particular plant was not vibrant green – as it should have been at that time of year, having emerged from its winter senescence – but brown and covered in holes. From this she knew the plant was dead. And once she had investigated further, she noticed there were many other cushion plants that had suffered the same fate. So too had the mosses and megaherbs that depend on Azorella macquariensis for their own survival.

‘It was a really holy fuck moment,’ Bergstrom says. ‘No one had seen it before because it is such a patchy landscape. It’s only because I had been going there since I was twenty-­one that I was able to notice what was going on.’

Back at the station, Bergstrom picked up the phone. The person she called was Dr Jennie Whinam.

Like Bergstrom, Whinam’s connection to subantarctic islands stretches back a long time. Her first visit to one was in 1987, when she travelled to Heard Island, 4,000 kilometres south-­west of Perth, as part of her PhD researching the ecology of peats. This was, she says, ‘the start of a lifelong passion for subantarctic islands’. The following year, she visited Macquarie Island for the first time and over the next three decades travelled to subantarctic islands roughly once every two years as part of her work with Tasmania’s Department of Primary Industries, Parks, Water and Environment.

‘Subantarctic islands are the places that grab my heart,’ she says. To her, they are ‘wild and sublime’. Indeed, she loves them so much that when she visits Hobart from her home, a thirty-­minute drive away, she will often make a concerted effort to go to the Subantarctic Plant House at the Royal Tasmanian Botanical Gardens ‘just to have that feeling of instantly being back’.

Whinam thinks of the vegetation on Macquarie Island as being like a ‘more extreme version of a Japanese garden. Everything is in miniature, so beautifully in place.’ And for her, the vast rolling cushions and terraces of Azorella macquariensis are intrinsic elements of the island’s floristic beauty. So when she answered Bergstrom’s call that day in December 2008 and learnt about the dieback, she was ‘immediately’ alarmed – especially because she had been on the island the previous year and hadn’t observed a hint of it at any of the sites Bergstrom had.

By the end of the following year, Whinam’s alarm had grown significantly after further surveys conducted by her and her colleagues revealed dieback at 88 per cent of 115 Azorella macquariensis sites. The worst examples of the dieback were located in the northern section of the island, where many of the cushion plants had completely died and been blown or washed away by the wind and rain, leaving nothing but gravel, or had been colonised by native grasses such as Agrostis magellanica.

This data ultimately led to the Australian Government listing the cushion plant as critically endangered in August 2010. ‘As far as I know, it was the first plant species to go from non-­listed to critically endangered in one leap,’ Whinam says.

The rapid speed at which the dieback was occurring was particularly shocking given that the incredibly harsh environment of Macquarie Island generally means that, as Whinam explains, ‘things grow slowly, and they die slowly. Until you get to a tipping point, and then everything suddenly falls over.’

Bergstrom and her colleagues hypothesised that the primary cause of this particular tipping point for Azorella macquariensis was seventeen consecutive years of drought that occurred in the larger context of Macquarie Island’s changing climate: over the past four decades, it has seen increased but more episodic rainfall, higher wind speed, less cloud cover and more sunshine hours, which has made it drier and warmer overall. This is problematic for a species such as Azorella macquariensis, which is particularly vulnerable to climate change because, as Bergstrom explains, it ‘has just thrown away features that would make it able to survive in drought’. Weakened and water-­stressed, the cushion plants were then more susceptible to pathogenic infection, which the chlorosis band on their canopies suggested was occurring.

In 2009, Whinam conducted sampling on multiple sites across Macquarie Island to try to identify the particular pathogen – or pathogens – in question. ‘We were under a lot of pressure because people wanted answers,’ she recalls. It didn’t help that poor weather limited the amount of time she and colleagues were able to spend in the field collecting samples. ‘We were frantically digging in the gravel and mud while it was pouring rain and howling wind,’ she recalls. ‘It was no spring picnic.’

A wide range of pathogens were detected in the samples Whinam collected. One that popped up in multiple samples was Pythium splendens. But like all of its counterparts, it wasn’t known to be fatal on its own. Adding to the mystery was that no evidence was found indicating that the rangers working on the pest eradication program had introduced a foreign pathogen to the island and were spreading it as they scoured the landscape for rabbits, rats and mice, which was what Whinam, Bergstrom and their colleagues had initially feared.

During the next few years it became clear that the mysterious soil-­borne pathogen had overtaken drought as the predominant cause of the dieback, with the telltale ‘yellow line of death’, as Whinam calls it, sweeping across the compact, green canopies of more and more cushion plants. Although they didn’t know what the pathogen was scientists such as Whinam came to believe that it had been latent on the island until it had started to flourish as a result of the recent shift in climate.

As concern about what was happening to Azorella macquariensis mounted, so too did the quest to properly quantify the health of the entire population and work out a conservation plan for it. Indeed, this was the focus of a multi-­year collaborative research project launched in 2015. Funded by the Australian Antarctic Division, the project was managed by Professor Melodie McGeoch from the Department of Ecology, Environment and Evolution at La Trobe University. Whinam and Bergstrom were among those involved in it, as was Dr Catherine Dickson, an experienced applied ecologist with a passion for threatened species and a background in environmental conservation in South Australia, who came on board as the lead field researcher.

Dickson’s first field trip to Macquarie Island as part of the project was in the summer of 2016–17 to survey the extent of the dieback across the island and determine the distribution and abundance of potential refugia for Azorella macquariensis. It was an especially wet and windy trip, with three monthly weather records on Macquarie Island broken in December 2016, and Dickson quickly learnt that conducting field work on a subantarctic island comes with unique risks – like falling into a putrid elephant-­seal wallow full of mud, urine, faeces, shed hair and moulted skin.

By the end of the trip in February 2017, Dickson had, with the help of colleagues including Bergstrom and Whinam, deployed microclimate data loggers, collected leaf samples and surveyed the cover and dieback of Azorella macquariensis at sixty-­two sites in various locations across the island – from very steep exposed slopes to more gentle sheltered ones and to fellfield peaks. The following summer she returned for two months to collect the microclimate data loggers and resurvey the condition of the critically endangered cushion plant at an additional twenty sites.

By then, much of the island’s vegetation had recovered significantly, since rabbits had been eradicated nearly a decade earlier. But Dickson’s work – for which she was ultimately awarded her PhD – revealed a more sobering story for Azorella macquariensis. She found, for instance, that the dieback of cushion plants was ongoing but highly variable across the island, with some surveyed sites showing near-­complete death of cushions and associated mosses, liverworts and megaherbs; that it had moved southward and was now centred on the middle of the island; and that it was more prominent in areas with a low number of freezing days and very high humidity – conditions known to be conducive to pathogenic infection and that are expected to become more common on Macquarie Island under climate change.

The research project officially came to an end in October 2019. Since then, no further major research into the dieback of Azorella macquariensis and the associated ecosystem collapse has been conducted, and the exact pathogen now believed to be driving the dieback remains unknown.

 

ON TOP OF Wireless Hill, located at the far northern end of Macquarie Island and so named because it was the site of a wireless radio station that linked the Australasian Antarctic Expedition’s main base in Antarctica with Hobart between 1911–14, there is an ex situ population of fifty-­four Azorella macquariensis plants growing in large white, irrigated buckets. Collected from different sites around the island in 2010 and 2013, these plants are carefully monitored via monthly photographs. At present they are in good health and are considered one of the best ways of conserving the species.

Another is the Azorella macquariensis seed bank stored at the Tasmanian Seed Conservation Centre, located in the Tasmanian Royal Botanical Gardens, a short stroll away from the Subantarctic Plant House. The seed bank contains just over 4,000 seeds, which horticultural botanist Natalie Tapson meticulously harvested by hand from 365 healthy cushion plants on Macquarie Island over several weeks in 2016. However, there is one major problem with the seeds: to date, scientists have been unable to work out how to break their inbuilt dormancy – to replicate the precise combination of conditions required for them to germinate.

But even if scientists are able to crack the secret germination code someday in the future – and even if they are able to identify the mysterious lethal pathogen and can then develop an effective fungicide – it is very unlikely that Azorella macquariensis will ever return to its former glory on Macquarie Island. That, at least, is Bergstrom’s belief, and she bases it on the fact that no serious action is being taken to mitigate the underlying driver of the dieback and the colonisation of areas once dominated by Azorella macquariensis by more resilient native grasses – that driver being climate change. Indeed, since the dieback was first discovered more than a decade ago, Macquarie Island has gotten even hotter: on 8 February 2022, it recorded its highest ever temperature of 17 degrees Celsius, more than 8 degrees hotter than the mean temperature for that time of year. The previous maximum temperature recorded on the island was 14.4 degrees Celsius in December 1984.

‘We’re so used to thinking we’re in control of nature and can come up with solutions to problems,’ Bergstrom says. ‘But I don’t think there is a solution here. I don’t think there is a happy ending.’

Looking into her scientific crystal ball, the future she pictures for Azorella macquariensis – a species with a genetic signature suggesting it has grown on Macquarie Island for roughly 200,000 years – is one where the ancient cushion plant will be locally extinct in many areas, confined to the few pockets with colder and wetter microclimates than elsewhere. Where it once formed vast terraces and carpets, there will either just be grassland or bare ground – a change that is already clearly visible across the island.

According to Bergstrom, this represents not only the transformation of an entire ecosystem but also the loss of ‘a defining component of the intrinsic wild value of the island’. It is a loss that she speaks about with tears in her eyes and a faint tremble in her soft voice – clear signs of ‘solastalgia’, the term coined by environmental philosopher Glenn Albrecht to refer to the ‘form of psychic or existential distress caused by environmental change’. And it is one that may very well be the first of many irreversible losses that occur throughout the subantarctic. As Whinam says: ‘It’s very possible that what we’re seeing on Macquarie Island, we might soon start to see on Heard Island or the other incredibly rich, biodiverse specks in the Southern Ocean.’

That this knowledge doesn’t seem to have any material impact – that so few people seem to care about it – can fill those who have been responsible for generating it over many decades with despair. ‘Sometimes I throw my hands up and say, “Fuck it. I’m just going to grow plants and spend all of my time in my garden,”’ Bergstrom says.

But – at least for the moment – she isn’t going to do this: ‘Because that’s being entirely self-­focused.’

Instead, Bergstrom and so many of her colleagues continue to direct their focus elsewhere: to science, to improving our understanding of how subantarctic and Antarctic environments are rapidly changing in a warming world – and, by extension, to holding us all to account for the environmental consequences our collective actions are having, including on one of the wildest and remotest pieces of land on Earth.

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