Those who are tempted to fall back on the old "sediment threat to the reef" chestnut can avoid ruining another pair of undies by reflecting on the fact that the reef has recently been a major beneficiary of anthropogenic change.

The new Dam on the Burdekin now traps just about all the silt in runoff from its vast catchment so there can be no doubt that the most populated part of the reef is now under substantially reduced pressure from both excess fresh water (which kills coral) and sedimentation.

And if anyone thinks this is not enough then all they have to do is support the construction of the Tully-Millstream Dam to do the same job further north.

To avoiding repeating myself:

http://forum.onlineopinion.com.au/thread.asp?article=5382#69529

:)

True Perseus, but is the virtual absence of a sediment plume and the reduction of the freshwater influence really good for the reef, or does it just change the species competition dynamics to the detriment of some species, as I mentioned in my last post?

Could it be that a new balance has been reached since the building of the Burdekin Dam and the capture of the enormous sediment loads due to overgrazing in the catchment? Could the impact on the reef from the current flood event be much greater than it would otherwise have been due to this new balance?

The reef has endured many storm events with their freshwater and sediment impacts over thousands of years, as is evident in the coral core record. It has also endured a greatly increased sediment load and then an instant virtual cessation of that impact, at least in the region off Townsville. And it has endured fishing pressure, bleaching events and so on, without any real consequences….as far as we know.

So while climate change and other anthropogenic factors will impact on it, and the species balance will change, I can’t see that the overall effect would be all that significant.

Now, this leads me to be in agreement with two people with whom I have found massive disagreement on this forum – Jennifer and ol’ Perseus the soiled underwear expert.

Yahoo! Wonders will never cease!!

Wonders never cease, Ludwig. But you do seem to be arguing that coral could have adapted to less fresh water since the Burdekin Dam but fresh water is the worst killer of coral. I also notice that all the bleaching events are close to the coast with next to nil bleaching in the outer reef. And this, given that there is still a lot of bleaching near the Burdekin Delta makes me suspect that the increased volume of urban storm water runoff is the culprit.

Urban development, without water tanks, currently turns half of each hectare of land into a 100% efficiency catchment. And in places like Airlie Beach, that means an extra 15 megalitres of coral poison for every ten new houses. Coastal urbanisation is the only change that has produced volumes sufficient to change inshore water salinity on the scale observed.

For all the rapid coastal development along the central and north Queensland coast, I can hardly imagine that stormwater runoff would be significantly greater in terms of impact on the reef, or even on inshore reefs.

I guess the key reefs to look at in Australia in terms of increased stormwater runoff effect would be the fringing reefs around Magnetic Island, just off Townsville which has grown enormously in recent times. I don’t know how they have changed over this period. Perhaps Peter Ridd can help us out here.

We need an expert to inform us of the causes of coral bleaching in various spots around the world, so that we can get a wider perspective of the possible effects of freshwater. The cause seems pretty categorically to be temperature-related.

Anyway, expanding the subject to the big picture: the effects of climate change are going to be mixed, and possibly even insignificant. All I can say is that we had better be prepared for a scenario that is towards the bad end of the spectrum, and that means getting stuck into preparations now.

Climate change is tooo big to handle! So rather than concentrating directly on dealing with it in Australia, we should be concentrating on the absolutely vital task of achieving sustainability. And in so doing, we would reduce greenhouse gas emissions more effectively than if we try to do it outside of a sustainability paradigm, ie with the continuous growth mentality still entrenched.

There is a need here to address some specific points that have been made in the original article and subsequent posts,

Article said - It will extend its range further south and this would be a good thing.
Firstly, there is minimal shallow water area along the East Australian coast south of the GBR, and most of it is siliceous sand.

Even if 'it' did 'move south', what would be left behind would probably be of different composition and ecosystem function. Same goes for the 'new' GBR to the south - is that a good thing? It is at a far greater level of complexity than a presence/absence issue.

Article said - Sea level rise will benefit corals
Sea level rise too gradual to be an issue in the context of benefiting the GBR before other climate change impacts.

Article said - Corals resistant to climate change and have/can adapt.
The issue here is that the rate and magnitude of this recent change is quicker than corals have had to deal with in the past

Ridd said "warming has increased the rate of growth of massive corals"
Firstly, this comes at the expense of coral skeleton density. Reduced skeletal density makes them much more prone to cyclones and storms. For long-lived, relatively slow growing massive corals, this has particular importance at the population level. Secondly, that pattern is not universal across all species.

"Moderate increases a good thing for the GBR"
It is not all about growth rates of adult colonies. Temperature affects many other properties, for eg., reproduction rates, larval dispersal and survival. This is a big topic, so I'll just touch on it. For example, for non-feeding coral larvae, increasing temperature may relate to quicker metabolism, quicker rates of development, therefore less potential to disperse far, therefore reduced connectivity among reefs and less potential to recover from disturbances.