Danger signs from a warming ocean

Jokes aside, our oceans are changing dramatically and permanently. [15 September 2014 | Peter Boyer]

As immigration minister Peter Dutton observed last week, for all the wrong reasons, time matters little when water is lapping at your door.

A seagrass meadow, an invaluable part of coastal marine ecosystems. PHOTO Heather Dine, Florida Keys National Marine Sanctuary

A seagrass meadow, an invaluable part of coastal marine ecosystems. PHOTO Heather Dine, Florida Keys National Marine Sanctuary

It was a bit of a joke that got a laugh out of Tony Abbott, but it’s no joke out in the Pacific where a rising ocean is making islands uninhabitable and threatening a refugee crisis.

The occasion was last week’s announcement by Messrs Abbott and Dutton that the government would be allowing in more Middle East refugees. It would be nice to think they’ve now grasped the irony of that situation.

But it bothers me that our political leaders treat such matters so lightly. The global ocean, the primary home of life on Earth, is today changing more rapidly and profoundly than for over 50 million years.

It’s bad enough that absorbing extra carbon dioxide from human emissions has made it more acidic, with big consequences for the marine food web.

But warming makes things much worse. Storing over 90 per cent of the sun’s heat energy reaching Earth, the ocean is now warming at great depth, and this will endure for many centuries. Rising sea level – warmer water takes up more space – is just one of many global implications.

A deadly consequence of a warming ocean is a lack of oxygen, which dissolves less readily in seawater as it warms. Like us, marine animals need oxygen to survive, and low ocean oxygen levels can wipe out entire ecosystems. In 2004 the UN Environment Programme reported 146 such “dead zones”, mostly inshore areas; four years later over 400 had been identified. Today these regions are estimated to extend over 10 per cent (and rising) of all ocean waters by surface area.

Dead zones occur where water circulation is poor, whereas most Tasmanian seas contain strong currents and are exposed to plenty of wind. But the warm East Australian Current is strengthening, creating a global ocean “hotspot” that’s dramatically changing marine life off our east coast.

Nature Climate Change has just published a seminal study by US and Australian-based scientists looking at changing distribution patterns of almost 13,000 fish and other marine species. It described huge changes to coastal marine habitats as a result of ocean heating.

Species living in a “thermal niche”, a narrow range of water temperature, must move to escape water that’s too warm. Species that can’t adapt or relocate to cooler waters will become extinct. If you’re a Tasmanian coastal species, for instance, there’s no escape to the south.

The arrival of species from warmer waters is a primary indicator that Tasmanian seas are warming. We know this because of Redmap, an outstanding citizen science program devised in Hobart and now tracking species distribution around Australia.

Observation records uploaded to the Redmap site show that sightings of immigrant species are on the increase around Tasmania. A notable recent addition was the gloomy octopus, normally found in waters off Sydney and further north but now breeding off Tasmania’s north coast. Associate Professor Gretta Pecl from Hobart’s Institute of Marine and Antarctic Studies says Redmap sightings are being used to guide future research strategies.

One of these is a program to control the long-spined sea urchin, another NSW invader now found right around the state. The urchin’s expanding range is creating “barrens” by destroying kelp and other vegetation – a bad omen for many dependent species. Large rock lobsters feed on the urchin, and IMAS scientists are currently studying how they can be utilised to control the invader.

Marine plants provide much more than a buffer against species loss and seabed erosion. Seagrass beds capture far more carbon than an equivalent area of rainforest and keep it locked away in ocean sediment for much longer. We really need a healthy ocean.

Next February, IMAS will host “Species on the Move”, an international conference in Hobart about the responses of species to climate change. It will include a public forum.

The annual Environmental Film Festival Australia (EFFA) is in Hobart for the first time this year (Friday till Sunday), showing the best of current environmental cinema at Village Cinemas and UTAS Sandy Bay. MORE INFORMATION.

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