Australia is losing the war to save the Great Barrier Reef, despite leading the world in environmental management, a leading marine scientist says.



Peter Doherty, research director at the Australian Institute of Marine Scientists, says the reef has suffered significant losses of coral, even in the years since the region has been World Heritage listed.



"These big actions we have taken certainly justify Australia's claim to have the best management of a large coral reef system," Dr Doherty told reporters at the International Coral Reef Symposium in Cairns on Monday.



"But the recent evidence is that we are not winning the war."



Dr Doherty told the conference over the last 27 years there has been an "alarming and unsustainable decline" in coral over large sections of the reef.



The United Nations Educational, Scientific and Cultural Organisation (UNESCO) recently released a report that was highly critical of Australia's management of the Great Barrier Reef.



It said the reef could be listed as a World Heritage site in danger unless high-risk coastal developments including new ports in Queensland are shelved.



The head of the Great Barrier Reef Marine Park Authority, Russell Reichelt, said his organisation was responding to UNESCO's concerns through the formation of a strategic assessment of the threats facing the reef.



"That assessment is critical for the assessment of the cumulative effects," Dr Reichelt said.



"It is decisions taken right now that will affect the next century and the potential long-term health of the Great Barrier Reef."