Rain Brings Rare Relief To Australia's Great Barrier Reef

[mrmoshe]

Rain Brings Rare Relief to Australia's Great Barrier Reef

The Great Barrier Reef is the world's largest living organism, stretching over more than 345,000 square kilometers. It is also the world's most protected marine area.

Still, it is under threat, from a combination of global warming, pollution and over-fishing.

Scientists had predicted that this summer would be a tough one for the reef. They feared that extreme heat would scorch the coral. But recent storms that dumped torrential rain across much of Australia's northeast have brought some unexpected good news.

The normally warm seas that cover the reef have been stirred, and Jeff Maynard of the Great Barrier Reef Marine Park Authority says the temperatures have dropped.

"This year reef temperatures are showing that temperatures for the majority of the Great Barrier Reef Marine Park are below the long-term averages we see for this time of year," he said. "So right now, we're considering coral bleaching risks to be low compared to bleaching years like '98 and 2002."

The future, however, still does not look good.

Bleaching occurs when unusually warm seas cause the organisms that make up the coral to die. All that is left is a white limestone skeleton.

Researchers believe that as the world's climate continues to change, the bleaching of the coral will become increasingly common.

The Great Barrier Reef, designated a World Heritage site, is Australia's most popular destination for tourists.

It is home to 1,500 types of fish, and at more than 2,000 kilometers long, it is the only living thing the naked eye can see from space.

[james1990]

I enjoyed reading about the GBR, there were some interesting facts in there i didn't know.

cheers james

[pjbink]

Bleaching is a completely natural event and is associated with prolonged periods of calm weather which leads to sharp rises in water temperature. From Dr Walter Starck:

In today's atmosphere of climate change alarmism the finding of totally unremarkable natural fluctuations can readily gain widespread attention and an appearance of importance by simply suggesting a connection with GW.

Bleaching events result from extended periods of calm weather during which mixing from wave action ceases and surface water becomes exceptionally warm. Such warming is especially marked in very shallow water such as on reef flats. At the same time the absence of waves also eliminates the wave driven currents that normally flush the reef top. Bleaching conditions require at least a week or more of calm weather to develop and this may happen every few years, only once in a century, or never, depending on geographic location. On the outer GBR it is uncommon due to ocean swell and currents even in calm weather. In the mid-shelf and inshore areas it is much more common due to the absence of swell and reduced currents.

Characteristic bleaching scars and isotope temperature records from coral cores commonly show evidence of past bleaching events going back thousands of years. There is no evidence for a recent increase in frequency and/or severity of bleaching events and nothing to link extended periods of calm winds with global warming.

In past geologic periods when global climate was warmer than at present corals enjoyed greater latitudinal distribution. The most likely effect of a warming climate on reefs would seem to be an expansion of their geographic distribution and there is some evidence this is already happening. In Florida recent growth of coral has occurred farther north than it did a few decades ago and in the same areas sub-fossil corals indicate previous such advances in the recent geologic past.

Hoegh-Guldberg has found an attractive GW niche in the well established guild of GBR doomscryers. It has provided notoriety, acclaim and generous research support. Whether his prophesies will stand up to the reality test remains to be seen. Based on the track record of science based doomscrying his odds don't look too good. In fact sheep's entrails and tea leaves seem to produce better results, probably because they at least incorporate some element of intuitive judgment."

The same coral species that have bleached on the GBR thrive elsewhere at considerably higher temperatures and in some bleaching locations subsequent events have shown less effect even at higher temperatures. The reason is believed to lie in differing clades of algal symbionts adapted to different temperatures. How far such adaptation can go is not known but species distributions of corals and associated water temperatures indicate that the temperatures associated with bleaching events on the GBR are several degrees below what the same coral species routinely survive elsewhere.

Combined with the AGW climate predictions of less warming at lower latitudes and past distributions of reefs in much warmer geologic periods a hollowing out in the middle seems unlikely. In any event it is wind (or rather lack of it) plus local geography and currents, not air temperature that is the key factor in bleaching events. On the GBR they are more likely to occur at the southern end of the reef than at the top where the strong currents of Torres Strait assures mixing and the flushing of reef tops even in calm weather.

Posted by: Walter Starck at April 12, 2006 03:36 PM

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Indeed storms do prevent bleaching. The recent storm up here (Cyclone Larry) has already been accredited with saving the reef from this years bleaching that had been predicted by OH-G. However we were already past the time of highest temperatures and calmest weather and temperatures were falling but, any storm in a punt.

Posted by: Walter Starck at April 12, 2006 03:46 PM

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*The 0.7 C. increase in temperature over the past century and a half coming out of the LIA is comparable to the rate of decrease entering into it.

* Corals can and do change their algal clades from one bleaching event to the next. They even do so seasonally without apparent bleaching.

*In a number of areas healthy corals tolerate seasonal temperature ranges of as much as 15 C. and at the high end this may regularly be 3-4 C higher than those on the GBR.

* Although bleaching does result in a temporary growth hiatus in corals the increased water temperatures over the past century has been associated with substantially increased growth and calcification.

* Intense tropical cyclones do immense damage to reefs but they are a natural element in many reef areas. Whether they will increase in frequency and intensity due to GW is unclear. Proponents of AGW claim they have. Storm experts say they there is no evidence for this. A storm like the recent one hitting the coast every few years would be far more devastating to humans than to the reef.