Tropical Sydney: Corals in the Harbour?

September 15th, 2014 · No Comments · Updates


Montage image presented at the recent 88th Australian Coral Reef Society conference in Brisbane.

By James Woodford

Welcome to Tropical Sydney, where a Manly Ferry ride could one day be a coral reef cruise.

Towards the end of her keynote address, at the 88th Australian Coral Reef Society conference in Brisbane, Dr Adriana Vergés, a marine ecologist at the University of New South Wales, flashed a slide onto the screen behind her.

It was a manipulated image of Sydney Harbour, half above and half below the water. The photo looked stereotypically glorious until the audience’s eyes wandered to what lay beneath the surface – a magnificent coral seascape in crystal clear water. There were plate and staghorn corals along with a cloud of tropical fish.

What made Dr Vergés’ montage of Sydney with a scene of coral reef from One Tree Island, off the southern Great Barrier Reef, so disconcerting was the fact that this was what the potentially ‘beautiful’ face of climate change might look like.

The picture’s message was this: The Great Barrier Reef is coming to Sydney, and bad is not necessarily ugly.

The image that Dr Vergés, presented to the nation’s leading coral ecologists led to an instant inhalation of shock followed by nervous giggles, then an outbreak of whispering among the scientists.

Dr Vergés talk was based on a scientific paper she recently wrote about the fact that seaweed-eating tropical fish are now able to survive in southern temperate waters and emerging evidence suggests they may be able to smash apart marine ecosystems in states like NSW. At the same time that fish from the tropics are starting to invade temperate rocky reefs, vast swathes of kelp forests are disappearing around the world.

While semis, high rise apartments and houses are fodder for land- based property booms, bare rock and reef beneath the water is an ecological housing bubble that never bursts. As soon as there is an empty space beneath the ocean, life competes fiercely to colonise it.

Dr Vergés demonstrated her point dramatically in her presentation with photographs from Tosa Bay in southern Japan. There, she says, seaweed has been replaced by coral colonies. At Tosa Bay there is no need to manipulate underwater photographs to demonstrate that corals are spreading into areas where they were previously unknown.

In the early 1990s the rocky reefs of Tosa Bay look like the kind of seaweed habitats that a scuba diver would see anywhere off southern NSW. By 2013 most of Tosa Bay’s kelps were toast and, in their place, magnificent corals that divers travel the world to see.

And the images of Tosa Bay are spectacular. Looking at them it is easy to imagine that many people would say that it is an improvement but it is a dramatic and enormously significant change. Seaweeds are marine algae and coral are animals. When you change who holds the reef real estate – seaweed or coral – then you dramatically change the reef.

After her talk I asked Dr Vergés about her slide and whether it was a joke.

“The ‘tropical Sydney’ slide I put up is really only half a joke – we certainly do expect marine communities to become increasingly tropical in the next few decades,” she said.

She added that other factors may prevent corals ever growing in Sydney Harbour, such as pollution and run-off.

Dr Alex sen Gupta, from UNSW’s Climate Change Research Centre said: “Using published, state-of-the art climate models and assuming ‘business as usual’ CO2 emissions, the projection is that ocean temperatures in the Sydney region will become ‘tropical’ – above 18 degrees in the winter and above 25 degrees in the summer – in just a few decades. More specifically, winter temperatures will probably consistently start exceeding 18oC between 2020 and 2030 while summer temperatures will probably start exceeding 25oC consistently between 2040 and 2060.”
According to Dr Vergés: ‘We already have evidence of coral expanding their distribution polewards along the east coast of Australia, and, again, the prediction would be that they will continue to do so.’

While the corals may not yet be establishing in Sydney it appears that tropical fish species are. The President of the Australian Coral Reef Society and University of Technology Sydney marine ecologist, Professor David Booth, has, for over a decade, been monitoring the arrival and increasing survival of fish that are normally associated with the Great Barrier Reef.

Dr Vergés joked to the scientists that while they may like the idea of coral reefs in Sydney, it would be an ecological catastrophe for all of the species that are displaced by warmer sea temperatures. And this massive shift in the world’s marine ecosystems is a story being repeated off coastlines around the world.


-James Woodford’s reporting was funded in part by the Pew Charitable Trusts


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