The Great Barrier Reef’s One Million Ton Sludge Problem by Darby Knight

Coral reefs, the rainforests of the oceans, are oases in the marine abyss, the most diverse and productive of natural ecosystems. Yet they can’t seem to catch a break. With oceans warming, more frequent extreme weather and marine waters acidifying, reefs globally are close to a potentially irreversible tipping point. Scientists and conservationists collectively wept when two back-to-back warming events caused coral bleaching in over 90% of the 1429-mile long Great Barrier Reef, with coral deaths ranging from 50-90%. Many media outlets printed eloquent obituaries for the fallen giant. The biggest of all reefs, you may presume we’ve since pulled our finger out to safeguard it from a further environmental onslaught. So, with another bleaching event thought to be imminent, why has the Australian government decided to dump one million tons of sludge on this world heritage site?

First let’s clarify what exactly coral is, and what bleaching does to it (it has nothing to do with cleaning chemicals). Coral reefs are made up of thousands of coral polyps, marine invertebrates related to jellyfish that live inside self-constructed exoskeletons. Inside each polyp lives symbiotic, photosynthetic algae that give the coral its colour and food. When ocean temperatures increase under extreme weather, stressed corals expel these algae, leading to the loss of food and ‘bleaching’ of colour. Corals start to die off, but the rate and intensity depend on the increase in temperature and how long the conditions persist. Thankfully, because they live in colonies of many thousands of clone individuals, corals are considered as modular organisms, meaning if some areas die they can recover later, making them somewhat resistant to the occasional bleaching event, but not immune to recurrent bleaching.

So, Australia: the Queensland government want to dredge out sediment to deepen one of the world’s largest coal loading ports, Hay Point, to ensure safe and reliable access for boats. In 2015, the Australian Federal government banned the dumping of sludge within the Great Barrier Reef’s boundaries, but that excluded sludge from maintenance projects, a small legal loophole that’s now being exploited. North Queensland Bulk Ports Corporation, who is responsible for Hay Point, state they’ve done a three-year, peer-reviewed study and worked closely with the Queensland government to keep the environmental risks low, but acknowledge they exist. The report suggests risks are “predominantly low with some temporary short-term impacts” which can be reduced if the sludge is dumped offshore where it will only (slightly) impact bottom-dwelling marine life.

What are these ‘small’ risks? There are fears the sludge may cause more coral bleaching if sediment blocks sunlight the symbiotic algae need to photosynthesise food for the corals, which will reduce coral growth and may lead to coral death. If the sediment is dumped in shallow waters, all organisms in the shallow seas will be smothered by sediment as nutrient cycles, water clarity and temperature are all disrupted. If reef-building corals are killed, the local reef framework risks collapse, though the immensity of the Great Barrier Reef makes the collapse of the entire reef highly unlikely. The sludge, regardless of where it is dumped, will contain toxic heavy metals. Corals can accumulate pollutants through filter feeding, and these metals can reduce or inhibit coral reproduction, further impacting reef regeneration after bleaching events. As for other reef-dwelling species, sedimentation drives reef fish out of their habitat as the number of shelters is reduced. As sedimentation is one of the main global threats to coral reefs, it defies logic why anyone would dump one million tons of it on the greatest reef in the world.

What’s even more mind-bending is last year the Australian government pledged AUS$500mn to protect the Great Barrier Reef. They listed sediment and agricultural runoff as a major threat. The recent flooding in Queensland has already washed masses of sediments, riddled with pesticides, into the Great Barrier Reef, which could smother corals or lead to algal blooms (of marine algae, not the important symbiotic algae). The $500mn plan itself was the result of threats by the United Nations to list the Great Barrier Reef marine park as ‘in danger’, so the funding is meant to be going towards reducing sedimentation, nitrogen deposition, run-off deposition and improving water quality. But scientists criticised the plan, saying the focus should be on climate change and that $500mn was 10% of the money needed to adequately protect the Reef. Water quality will only worsen with this dumping of sludge.

What was the point of banning sludge dumping and investing in a big-money conservation initiative if the government is going to exploit loopholes and ignore their own bankrolled schemes? As far as opposition goes, Greens Senator Larissa Waters has argued that the permit should be overturned, but it may be too late for that. It’s not just sludge being dumped as waste, but also the money put aside to give the Great Barrier Reef a future. The Reef’s problems aren’t going to get much easier.


Ali, A-h. A. M., Hamed, M. A. and El-Azim, H. (2011), Heavy metals distribution in the coral reef ecosystems of the Northern Red Sea, Helgol. Mar. Res., Vol 65, pp.67–80

Barus, B. T., Prartano, T. and Soedarma, d. D. (2018), CORRELATION OF SEDIMENTATION WITH PERCENT COVER CORAL REEF IN LAMPUNG BAY, Jurnal Ilmu dan Teknologi Kelautan Tropis, Vol 10(1), pp. 49-57

BBC News (2019), Great Barrier Reef: One million tonnes of sludge to be dumped, [Last Accessed 05/03/2019]

Bell, P. R. F., Greenfield, P. F., Hawker, D. and Connell, D. (1989), THE IMPACT OF WASTE DISCHARGES ON CORAL REEF REGIONS, Wul. Sci. Tech., Vol 21(1), pp.121-130

Coral Reef Studies (2016), 2016 global coral bleaching: Never a greater need for coral reef research, ARC Centre of Excellence, Annual Report 2016, [Last Accessed 05/03/2019]

Daley, J. (2019), Australia Allows One Million Tons of Sludge to Be Dumped on Great Barrier Reef, Smithsonian Magazine, [Last Accessed 05/03/2019]

Graham, N. A. J., McClanahan, T. R., MacNeil, A. et al. (2008), Climate Warming, Marine Protected Areas and the Ocean-Scale Integrity of Coral Reef Ecosystems, PLoS ONE, Vol 3(8), e3039, DOI: 10.1371/journal.pone.0003039

This site was designed with the
website builder. Create your website today.
Start Now