Great Barrier Reef tested for flood damage

Authorities are monitoring for tell-tale signs of damage as muddy flood plumes smother 10% of the GBR.

A NASA satellite shows a muddy plume heading for the GBR from the Burdekin River on 4 Jan (Photo: NASA/Norman Kuring).

TURBID FLOODWATERS FLOWING into the Great Barrier Reef (GBR) may cause an explosion in algal blooms and coral bleaching, authorities have warned.

The Fitzroy, Burnett and Thompson rivers have flushed floodwaters into the reef's inshore areas, particularly off the central Queensland coast near Rockhampton.

Though the reef runs for 2300 km down the coast of Queensland, research from James Cook University has revealed that the muddy plumes are already covering more than 10 per cent of its surface area.

The Great Barrier Reef Marine Park Authority (GBRMPA) is mapping the floodwaters and testing samples for pesticides, salinity, turbidity and temperature anomalies. So far the plumes are not affecting popular tourism locations in the Whitsundays, Cairns or Port Douglas, it says.

Floods killing the coral

The most immediate threat is from the freshwater itself which kills coral; nutrient- and pesticide-rich waters can also smother corals and encourage blooms of algae and other competitors.

The risk doesn't end when the floodwater stop flowing, according to Dr Britta Schaffelke, with the Australian Institute of Marine Science in Townsville. "After flooding we see an increased incidence of disease," she told the British science journal Nature this week.

"So even if the coral initially survive, over the next few months they might still die, or not reproduce, or reduce their growth rate," she said. "They would also be less resilient to any subsequent bleaching events caused by periods of very warm weather, an event that has already struck the reef twice in the past decade and is predicted to become more common due to climate change." 

Extent of damage on Great Barrier Reef not known

"It will be some time before we know the full extent of damage caused by the flood plume," says GBRMPA spokesman Andrew Skeat. "[But] even when ecosystems are exposed to freshwater plumes they do not necessarily die."

The flood run-off, full of sediment and nutrients, could spark increased algal blooms, coral bleaching and coral diseases, he agrees. It could also increase the productivity of some inshore species such as barramundi, mangrove jack, some prawns and sponges.

"Many plants and animals have mechanisms to cope ... however, this event has unusually large amounts of flood run-off with suspended material and the prevailing conditions may be different to previous events."

Significant impact to be seen on marine life

Environmental groups have also expressed wide concerns.

"The plumes of sediment and debris generated by flooding on this scale can have a wide range of impacts on marine habitats and species," said a statement released by the Australian Marine Conservation Society. "From entanglement of marine life in debris such as plastic bags to the smothering effects of large amounts of deposited sediments on sensitive habitats like seagrass meadows and coral reefs."

WWF-Australia, based in Sydney, has warned against the "disastrous impact" on corals and species including dugongs and turtles.

"In addition to the terrible costs to farmers and communities in Queensland, we will also see a major and extremely harmful decline in water quality on the Great Barrier Reef," says Nick Heath, program leader for water.

"Today's floods are bigger, dirtier and more dangerous from excessive tree clearing, overgrazing and soil compaction. As a result less water infiltrates deep into the soil, increasing the size and erosive intensity of floods," he adds.

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Home to a warm climate and the crystal clear waters of the Whitsunday Islands, Queensland is a tropical paradise. Off the coast lies the Great Barrier Reef, a breathtaking coral system abounding in exotic fish and spectacular colours. The lush World Heritage-listed Daintree forest in the far north provide some relief from the heat, while further inland, the Simpson Desert’s earthy red dunes offer a stark change of scene.