A world-first study has found that dredging can more than double the level of coral disease in reefs.
Scientists have known for decades that dredging can smother corals, but researchers say this is the first time it has been linked to diseases.
With dredging approved in the world heritage listed Great Barrier Reef Marine Park, the scientists hope their work draws attention to the pressing issues facing the region.
The study by the Australian Research Council’s Coral Reef Studies Centre of Excellence looked at the 7 million cubic metres of dredging done for Chevron’s Gorgon Gas Project off Western Australia’s coast.
“There was a fair bit of dredging going there and this was an ideal opportunity to use this natural experiment to look at the impacts of dredging, sediment and turbidity on coral health,” lead author Joe Pollock said.
“What we’ve found is that you get two times as much coral disease near the dredge sites as you do at nearby control sites.”
Not all diseases are fatal but Mr Pollock said they can have a significant impact on reef health.
“When you have disease, once that disease lesion’s passed over a bit of coral, it’s completely dead and it’s never recovering,” he said.
“They don’t get attention as much as they probably should but within scientific communities it’s known that coral disease actually kills more corals every year on the Great Barrier Reef than bleaching does.
“They’re something that’s critical to understand if you want to be able to manage different sorts of dredging projects or other sorts of developing projects.”
Chevron said it always anticipated some coral would be impacted by dredging activities.
“[The] coral loss remains a third less than the limit approved by the government regulator,” the company said.
Study backs Great Barrier Reef dumping projections
This research will be crucial, with dredging already approved in the Great Barrier Reef Marine Park Area.
North Queensland Bulk Ports Corporation has approval to dredge and dump 3 million cubic metres of sand and silt in the marine park.
The dumping is currently the subject of a legal challenge and it is not clear whether dredging will go ahead next year.
The ports corporation said it welcomed the study and that its dredging and dumping would not be so close to the reef.
Environment manager Kevin Kane says the research supports the company’s internal work.
“The impacts associated with dredging are quite isolated,” he said.
“They’re local impacts, they’re certainly not regional on a scale, they’re certainly not reef-wide on a scale.
“So this research really does assist us in understanding that further. It’s really just another layer that adds to some certainty about the management options that we take.”
Mr Pollock is hopeful the work highlights the pressures that all reefs are facing.
“When we look at the Great Barrier Reef and reefs around the world, it’s not just dredging that’s impacting them,” he said.
“They have to deal with climate change, they have to deal with nutrients coming into the water column and then when you add on top of that the stress associated with dredging – sometimes it can be too much.
“The fear is you can get these coral reefs over a threshold where they shift from coral dominated to algae dominated reefs.”