PREVIEW

Just offshore of the Tasman Peninsula in southern Australia, giant kelp plants used to compose a dramatic seascape which drew divers the world over.

By 2024, Eaglehawk Dive Centre heads Karen Gowlett-Holmes and Mick Baron reported that the original underwater forest was not only “threatened” – as described by the Australian Government – but had disappeared entirely.

“In southern Australia, just looking at shallow water – and I’m talking here from… 20-30 metres – we can probably put names on possibly 30% of the species that we have. The other 70%, we do not have names for,” Karen explained in the short documentary Reviving Giants: A Journey into the Restoration of Tasmania’s Giant Kelp Forests by the Great Southern Reef organisation. “They are undescribed, and as the climate’s changing so fast, they’re actually becoming extinct before we even know that they’re there.”

Mick added, “The giant kelp used to be so thick down here, you couldn’t drive a boat through it, you couldn’t put a pot in it, you couldn’t set a net in it, you couldn’t operate a hooker diving gear through it. So, basically, it acted as a natural nursery of its own accord.

“And then over a period of about 15 to 20 years, it’s all disappeared… By the end of March 2016, there was not a single plant left.”

However, a restoration project in one bay on the southern tip of Tasmania has been bringing these giants back to life.

Mick, alongside biologist Craig Sanderson, began the project seven years ago.

They started hand-planting juvenile giant kelp by tying the plants to bricks so they would anchor to the sea bed.

“Lo and behold, some of them grew,” Mick celebrated to ABC News. “They went from things you could hardly see on the strings to plants over 10 metres high in 18 months.”

But over the years, both juvenile and adult plants were continually washed away.

“They were so thin and sparse and had a lot of buoyancy, and the buoyancy would lift the bricks,” Mick explained. “They'd float away and get destroyed on the shore.”
A group of Institute of Marine and Antarctic Studies (IMAS) scientists have refined the approach.

Instead of acquiring juvenile plants and tying them to bricks, the scientists have been growing the giant kelp from seeds in a laboratory, then tying them with twine to PVC piping and grafting the arrangement to smaller kelp species which are already established in the reef.

“(The roots) hold fast to existing kelp and are fantastic,” project coordinator Scott Bennet gushed. “That pins the twine in place, and the giant kelp grows quickly… and attaches itself to the rock and substrate underneath.”

Eighteen months after attempting this new method, the giant kelp has grown – and hasn't floated away.

Now, a field of giant kelp spanning 3,500 square metres has covered this Tasmanian bay.

But the burgeoning underwater forest remains vulnerable to rising ocean temperatures.

Though the Tasman Peninsula waters usually measure at 16-17 degrees Celsius, a marine heatwave which began in December saw the bay at 20 degrees Celsius by late February.
“A lot of the large established plants are very stressed and have died back from the surface,” Scott said of the heatwave’s impact. “However, importantly, the lower parts of the kelps are surviving. So we are hopeful they will bounce back over autumn, once temperatures recede.”

He concluded, “It's mind-boggling when we think back to how rich and productive these reefs were, and now that is entirely gone. At the same time, there is a lot of hope that we can bring back some of that.”