Tasmanian kelp forest (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.

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

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