THE Great Barrier Reef (GBR) is in excellent shape - farming and other human activity are not killing the reef, according to James Cook University's reef scientist Dr Peter Ridd.
As a physical oceanographer, his area of interest has been sediment transportation, and his conclusion is there is no significant threat to the reef from human activity and he is adamant cane farmers are not killing the GBR.
"But we are dealing with an important ecosystem so we can't be too complacent," he said.
"If you can minimise your nutrient loads (from farming), you'd be stupid not to, particularly if it reduces your cost of production without harming your crop size."
With regard to proposed legislation, he said whatever priorities are set, they need to be based on good, un-emotive science.
With 25 years of Great Barrier Reef (GBR) research behind him, James Cook University's Dr Peter Ridd has studied the reef ecosystem longer than have most 'eminent' scientists.
He recently told the Australian Cane Farmers Association conference delegates there is no better coral reef ecosystem than the GBR - itias virtually undisturbed, and most is well offshore.
He said there are scientists who say global warming will kill the reef within 60 years.
Some say nutrient and pesticide increases, crown of thorn starfish and ocean acidification will kill it within 30 years, but none of those threats can be substantiated, particularly global warming, as coral is a tropical species which improves in growth rate and health as water temperature rises.
However, getting back to human effects on the reef he said: "We are used to seeing photographs of muddy flood water along the coast and there is no doubt the sediment has increased due to agricultural activity, possibly in the order of 10 times.
"But sediment loads within river outflows are in the order of 1-10 milligrams/litre. They only last a few days each year and they never reach the outer reef.
"By contrast, our research shows the resuspension of sediment by wave action during a 25-knot SE wind is in the order of 10-100mg/L, which happens for a few days every month and it's not sediment that's been deposited in recent times. It's been there since the sea level rose 80,000 years ago.
"The amount that's been added since European settlement is only a very small fraction of what's there. So it would be difficult to make a case that the sediment in a river plume would harm the inshore corals.
"In fact, the top 20cm of sediment on the seabed of the Coral Sea (the depth to which resuspension occurs) contains 500 times the nitrogen and phosphorus of a river plume.
"Biologists tell us the inshore reefs, with only 10 to 20 coral species, are a 'degraded system' because they don't have hundreds of species like the outer reef, but that's like comparing the rainforest in the wet tropics with the desert scrub of Central Australia.
"You can't say the desert scrub is a degraded rainforest, so as the inshore reefs have a different environment, they are composed of corals that are able to thrive in water with high turbidity and nutrient loads.
"Once that was recognised (by the scientists), the focus changed to the nitrogen and phosphorus contained in the run-off from the land and how it affected the whole reef, not just the inshore corals.
"The question needing an answer was: 'Can the results of human activity increase the levels of nutrients across the entire reef for a significant period of time each year?'
"We worked out a set of calculations to discover how long it takes a drop of water to be flushed out of the reef system into the Pacific Ocean.
"We found water in the outer reef was gone within two weeks, and from a river mouth, a month or at the most, two months. And we are not talking about small amounts of water, we're dealing with cubic kilometres of water as the GBR is a very open system.
"Our other calculations, even pushing the limits of probability, show a river plume could increase the N and P levels in inshore waters by 20 percent and in the outer reef by 3pc.
"However, compared to what is already out there and the small time it is in the environment, it is insignificant.
"There is algae growing amongst the corals on the reef that act like legumes and produce more than 20 times the amount of N of a river flow.
"Then there are upwellings of nutrient-rich water from the Pacific that flood over the reef containing 100 times the N and P of the river discharges.
"So it would be virtually impossible to quantify the effect of man-induced increases in nutrients as they are so small."
Regarding herbicides in river water Dr Ridd said the dilution factor ensures it would have no effect on the outer reef but there was a slight possibility it could have an effect on inshore reefs.
"But we can't point to any single reef and say it is significantly different from what is was when Captain Cook sailed up the coast.
"It may have changed due to a flood, a cyclone or coral bleaching, but it repairs itself over time.
"By contrast, on the land we can see erosion, introduced weeds and feral animals all causing environmental degradation and funding for research and control is being reduced, whereas funding for the GBR, where no degradation is measurable, is increasing and I would like to see that reversed.
"Also, unlike most other coral reef systems of the world, herbivorous fish are not harvested on the GBR – our catch is all carnivorous fish, which leaves the herbivorous species to keep algae under control and the reef is in pristine condition."