Murky freshwater run-off from Australia’s worst flooding in decades is adding to stresses from pollution and warming seas on the Great Barrier Reef, one of the world’s most fragile ecosystems.
Researchers say it is too early to know exactly how much of the reef has been affected by the flooding, which carved a wide path of destruction on land before draining into the sea off the country’s north-east coast.
So far, the signs are that damage will be isolated to relatively small portions of the reef, a popular dive site and network of coral structures rich in marine life that stretches more than 1,800 miles along the coast.
A narrow band of the reef was battered by a massive cyclone that passed overhead earlier this month and struck the coast with winds of up to 170 miles per hour, though the Great Barrier Reef Marine Park Authority that manages the area said damage such as coral breakage was probably limited.
More worrying than the cyclone are the effects of the recent floods, which sent huge plumes of muddy fresh water over coastal portions of the reef, said Ove Hoegh-Guldberg, a reef expert from the University of Queensland.
Floodwater can hurt reefs in many ways, as coral becomes stressed when the level of salt in the water drops, the high concentration of soil nutrients in floodwater provides food for coral competitors such as certain types of algae, and pesticides in the water can kill the coral outright.
In recent years, the reef has suffered from mass bleaching, in which coral under stress expels the colourful algae living in its tissues, and many scientists believe rising sea temperatures are responsible for the bleaching, which can eventually kill the coral.
Drenching rains that pounded Queensland for months sent swollen rivers over their banks, inundating communities as the water made its way downstream to the ocean. Entire towns were swamped, 35 people were killed and more than 35,000 homes damaged or destroyed.
Nick Graham, a senior research fellow at Queensland’s James Cook University, said many parts of the reef closer to shore have adapted to floodwaters, which have become common in the rainy summer season, although it’s too early to say for certain what additional damage may have been done by the recent floods.
Coral ecologist Alison Jones has been examining several reefs in the Keppel Islands, an area in the reef’s southern tail where floodwaters spilled into the sea, and found isolated damage to coral in waters less than 2 metres deep.