Ocean heatwave destroys Tasmania’s unique underwater jungle

The last giant kelp forest on the east coast of Tasmania has been lost, report divers and scientists

Giant kelp forests can grow up to 45m tall, but scientists have told senators that it will not survive into next century at current rates of warming. (Photo: Emma Flukes)


It was one of Australia’s great marine ecosystems; a must-see spectacular on many divers’ lists, sheltering a multitude of fish, algae and crustaceans.

A natural wonder, which this year was smashed into oblivion by a massive underwater heatwave.

This is not the Great Barrier Reef, but its southern equivalent; an underwater jungle that in the middle of last century ran 250 kilometres along Tasmania’s east coast. The trees, up to 45m tall, were Macrocystis pyrifera – giant kelp – the world’s largest seaweed.

In pictures: creatures of Tasmania’s disappearing kelp forests

Last week, Mick Baron, a dive operator and marine biologist, went to search for a patch on the inner coves of Munroe Bight at the extreme southern end of the east coast. It was the last patch remaining of the great eastern forest that once choked the unbroken 250km stretch of coast from Eddystone Point to the Tasman peninsula. But when Baron arrived, an almighty storm had ripped the trees from the rocks below.

Baron has dived on the east coast since the 1970s. Back then it was impossible to get a boat through the thick mats of canopy it left floating on the surface. “All those years ago it was everywhere. I mean it was common as muck,” he says. “Now it’s just gone.”

Tasmanian kelp forest. Photo: Emma Flukes

This kelp forest in Lagoon Bay on the east coast was destroyed this winter by a combination of warm water stress and heavy storms. Photo: Emma Flukes

It has been an extraordinarily rapid decline. But unlike deforestation on land, these forests are neither being cut nor burned. They are being starved.

The Australian arm of the huge gyre that moves water around the Pacific is the East Australian Current (known to Finding Nemo fans as “the EAC dude”). Traditionally it pushed warm water south along the coast of the mainland before turning east toward South America long before it hit Tasmania.

In recent decades, something has gone awry. The warming global climate has discombobulated this once-reliable system. Huge eddies of hot, nutrient-poor water keep spinning down toward the Tasmanian coast.

Because of this, eastern Tasmania has some of the fastest warming ocean water on earth, rising two to three times faster than the global average. Over the last two decades, says Baron, the ocean has been getting “more and more rapidly mad”. Tiger sharks, marlin and Queensland grouper have all been recorded in places where they have no right to be. This February, one tuna fisherman had caught 500 southern bluefin before their normal season had even begun.

The current is bringing change, but it doesn’t carry the nitrogen that the forests need to fuel their prodigious growth rate.

“You get a double-whammy for the giant kelp. They get stressed because of heat and they get nutrient-starved and that combination is lethal,” says Thomas Wernberg from the University of Western Australia.

Weedy sea dragon, Tasmania. Photo: Emma Flukes

Weedy sea dragon, Tasmania (Photo: Emma Flukes)

Last year, the EAC sent down its biggest belch of hot water yet: an extreme and unprecedented heatwave that sent temperatures soaring through December and staying high for the whole summer. In those conditions, the kelp simply cannot regrow after the winter storms.

The warm eddies have not yet turned past the Tasman peninsula, leaving some giant kelp beds on the island’s remote southern and western coastlines. Craig Johnson, associate director of the Institute for Marine and Antarctic Studies in Tasmania, says he feels optimistic that those will remain for a while longer.

“But you only need to have one or two of those heatwave conditions happen and they’ll disappear quickly enough,” he says.

Wernberg calls the giant kelp the panda of Australia’s temperate waters, “because it’s big and charismatic and probably doomed for extinction”. He is modelling giant kelp’s future and initial results suggest the warming climate will eliminate all giant kelp from Australia by the end of the century.

Tasmanian kelp forest. Photo: Emma Flukes

Tasmanian kelp forest (Photo: Emma Flukes)

Johnson agrees with Wernberg’s rough timeframe. The crash, he says, brings an end to an ecosystem that has dominated Tasmania’s east coast for tens of thousands of years.

“It’s been the iconic shallow water rocky reef ecosystem. They are phenomenal places, both from a scientific and aesthetic point of view,” he says.

Giant kelp is abundant in other parts of the world, including California and South Africa. But it is not just a single species at risk. Like the eucalypti that line Tasmania’s coastline above the water, the kelp trees are themselves a habitat.

“You imagine the water between five and twenty metres in depth in semi-sheltered areas all the way up the east coast of Tassie filled with eucalyptus trees,” says Baron. “Imagine how much surface area all that massive forest is offering to all the little beasties that settle on it.”

Those little beasties are a group of marine animals and plants that Wernberg says is the “most unique in the world in terms of endemic species”. Only in these waters can you find the weedy sea dragon, the delicate parrot of the kelp jungle, flitting in slow-motion among the branches. Around 30% of southern Australia’s fish species exist nowhere else. For seaweeds that number goes up to around 80%.

Video taken in 2012 and 2013 in Fortescue Bay and Munroe Bight, eastern Tasmania. These forests have now been confirmed lost. Video:
Rebecca Ramaley

In 2012, giant kelp forests were listed as an endangered ecological community by Australia’s government, the first marine community to be considered as such.

“[In the media] it’s all about the tropical coral reefs, but temperate reefs are actually equally important and bio-diverse,” he says.

As the kelp forests decline, other forms of smaller kelp can replace them. The complex structure of the forest is lost along with the massive capacity for capturing nutrients and recycling them into the surrounding waters. But with increasing frequency, the forests are being replaced with nightmarish “urchin barrens”.

The warming seas are now warm enough to support the spawning of the long-spined sea urchin, an invasive pest that scours the seafloor. Giant kelp normally booms and busts, ripped away by storms before reclaiming the territory. But now the urchins move in like a herd of underwater goats, nibbling away the new strands of kelp before they can grow beyond their reach. The result is acres of bare rock, covered with black, spiny invaders.

Overgrazing by the long-spined sea urchin results in the formation of sea urchin “barrens” – vast moonscapes of bare rock totally denuded of kelp growth. Formation of urchin barrens results in loss of biodiversity and ecosystem function for reef inhabitants that depend on kelp beds for food and shelter. Deal Island, Bass Strait, Tasmania. Photo: Emma Flukes

Overgrazing by the long-spined sea urchin results in the formation of urchin barrens. Deal Island, Bass Strait, Tasmania. Photo: Emma Flukes

Johnson believes that overfishing of the local rock lobsters – known down here as crayfish – has allowed the urchins to establish themselves in plague proportions.

All of this spells disaster for Baron, who is of a breed of unimpeachably frank Tasmanians and doesn’t try to gloss the details. The loss of the last forest from their stretch of coast means a business built on their beauty will inevitably decline. Already his Eaglehawk Dive Centre has had cancellations. Despite many other diving attractions, it was the forests people wanted to see.

“It won’t be long before I’m doing other things,” he says.

Tasmanians that Climate Home spoke to were traumatised to hear the news that this great ecosystem had been so categorically destroyed. Divers who had seen it returned misty-eyed accounts, describing a feeling of flight as they drifted through the trunks. It’s cold and challenging, says Baron, but ever so worth it.

“Once you get down underneath it it’s a totally different world. And most people never see it unfortunately.”

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