An independent study has revealed the significant effect dredging has on coral reefs, contradicting claims made by the federal government and port developers that dredging at Abbot Point would have ''minimal impact'' on the Great Barrier Reef.
A world-first survey examining the link between dredging and coral diseases found double the amount of diseased coral at reefs nearby dredging sites.
Joe Pollock, the study's leader from the ARC Centre of Excellence for Coral Reef Studies, said dredging increased water turbidity, meaning there was less light for corals to photosynthesise. Dredging also increased the level of sediment falling on coral that could interfere with their feeding.
''Just like in any other organism, it seems that chronic stress can lead to increased levels of disease in corals,'' said Mr Pollock, whose study was conducted near Barrow Island, off the West Australian coast, close to where 7 million cubic metres of silt and sand was dredged.
As part of the port expansion at Abbot Point near Bowen in north Queensland, 3 million cubic metres of sand and silt will be dredged and dumped in the World Heritage-listed marine park area, a decision criticised by UNESCO's World Heritage Committee, who will decide whether to classify the reef as "in danger" next year.
In an interview last year with ABC's 7.30, Environment Minister Greg Hunt said the scientific advice he had received suggested the port expansion would have "minimal impact" on the reef. Port authorities also claim any dredging impacts are local.
Mr Pollock's survey, published in the journal PLoS One on Thursday, found reefs exposed to the sediment plume for more than 290 days had double the amount of disease, mostly white syndrome, where tissue peels off the coral's skeleton, a condition that can kill the entire colony. The study, conducted one month after the 18-month dredging project finished, also measured a 10-fold increase in bleaching.
Evidence from another recent study has also refuted the claim that port activities only have a localised impact on the reef.
Kathryn Burns from James Cook University found evidence of coal dust originating from coastal coal terminals had spread across a vast stretch of the Great Barrier Reef.
Professor Burns' research, published in the journal Estuarine, Coastal and Shelf Science, found the chemicals from the shoreline out to 100 kilometres off the coast. In some locations, chemicals exceeded international toxicity guidelines.
Professor Burns said given her samples were collected in 2009 and 2011 before the present port expansions, further contamination of the GBR lagoon was likely following the expansion of coal ports at Abbot Point and Hay Point.
Terry Hughes, the director of the coral reef studies centre, said the findings were a "game changer".
"It's not just a case of lifting up sand and putting it somewhere else where it stays put," Professor Hughes said.
He said the findings of both studies showed how dredge spoil travelled a long way, could contain toxic chemicals and increased the rate of coral diseases.
"It's not coincidental that this new information from the west coast and the east coast is coming from the scientific community, not people with a vested interest in dredging," he said.
One of the conditions of the government's approval for the Abbot Point dredging was that developers had to achieve a 150 per cent improvement in water quality in the marine park overall.
But a UNESCO report released in May says the federal government's plan to achieve a 150 per cent net benefit in the reef's overall water quality to compensate for the impact of dredging at Abbot Point ''appears inappropriate'', partly because of the ''uncertainty about the impacts of dredge material plumes beyond the disposal site''.
Minister Hunt said developers were required to meet strict conditions on water quality, and regularly demonstrate their adherence.
"The disposal of sediment will occur over 40 kilometres away from significant coral reefs to ensure that those coral reefs are not exposed to the high sediment and turbidity levels that occurred in the marine waters of Western Australia," he said.