As muddy river water swept through parts of Australia, inundating more than 20,000 homes and claiming at least 15 lives, it also poured into the ocean, where it now threatens one of the country’s most precious natural ecosystems: The Great Barrier Reef.
The reef’s already vulnerable coral and marine life is getting flushed with fresh water carrying massive amounts of dirt and mud, nutrients and pesticides from farm runoff.
The Great Barrier Reef is long and vast, stretching 1,430 miles along Australia’s northern coast. Its coral reefs provide habitat and hiding places for tens of thousands of species. The shoreline is the hardest hit by the floods, with flood plumes remaining pressed against the shore by winds and tide.
Coral reefs have endured flooding in the past, but today’s floods are bigger, dirtier and more dangerous, scientists say.
“Freshwater discharge has always occurred but not with the loads of pollutants we now see,” says Jon Brodie, Principle Researcher for James Cook University’s Australian Centre for Tropical Freshwater Research.
Corals are sensitive to any environmental disturbance, and the high level of sediments, mass amounts of fresh water and nutrients from fertilizers and other toxic chemicals all pose high risk. And coral is already weakened by destructive fishing, ocean acidification and warming water temperatures, which cause bleaching, and death.
“The coral reefs now affected have been seeing floods for many hundreds of years,” says Katharina Fabricius, principal research scientist for the Australian Institute of Marine Science. “What has changed is that the loads of nutrients, and sediments have increased four to tenfold.”
Fresh water reduces the seawater’s salinity, killing coral. All topsoil carries nutrients, which can smother and clog the corals and block photosynthesis. And sediments remaining for a long time in the system could lead to the unchecked growth of algae blooms and reduced biodiversity, as well as an outbreak of crown-of-thorns starfish, a sea star that preys upon coral, Fabricius says.
Each female starfish produces 60 million eggs, and scientists are concerned that a flood might produce the first outbreak in 15 years.
Plus, seagrass beds and mangroves, which also may be damaged from the floods, normally help to filter out dangerous sediments, says Helen Fox, senior marine scientist in the World Wildlife Fund’s conservation science program. “And you can imagine how big flooding events literally swamp their ability to do that.”
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