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Originally posted by Adam
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Adam,
The argument that corals are somehow slowly dying at temps below 80-84 just doesn't hold water. Many aquarists (myself included) have watched a wide variety of corals grow very quickly at temps in the 78 degree range. Why would an animal fighting for it's very life waste energy on growth?
The corals that grow well at low temperatures are primarily species of
Pocillopora and
Stylopora that have secondary low thermal optima - a secondary growth peak at about 79 to 80 deg. F, in
addition to their main growth peak at 84 deg F.
The properties of low temperature mortality are well-known and documented. They happen in all poikilothermic animals and corals are no exception. You may wish to read about them in the reference below.
Prosser, C. L. 1991. Comparative Animal Physiology, 4th ed.. Environmental and metabolic animal physiology. Wiley-Liss, New York, 578 pp.
. Even if you do believe that the average (over several years) temperature of all the reefs is 82, how long has it been that way in evolutionary terms??
The data on average temperatures are available here from measurements of over 1000 reefs compiled before the recent warming events:
Kleypas, J. A., J. W. McManus, and L. A. B. Menez. 1999. Environmental Limits to Coral Reef Development: Where Do We Draw The Line. American Zoologist. 39:146-159.
You may not choose to accept these data, but the scientific community does.
We have good, very precise, data on reef temperatures going back several hundred years, but of course you may choose to ignore those data too.
Lough, J. M. and D. J. Barnes. 1997. Centuries-long records of coral growth on the Great Barrier Reef. Great Barrier Reef Marine Park Authority Workshop Series. 23:149-157.
Quinn, T. M., T. J. Crowley, F. W. Taylor, C. Henin, P. Joannot and Y. Join. 1998. A multicentury stable isotope record from a New Caledonia coral: interannual and decadal sea surface temperature variability in the southwest Pacific since 1657 A.D. Paleoceanography. 13:412-426.
[b] The data is sketchy for surface seawater temps when you go back more than a few years, but we know that average global temps are up in recent years, so wouldn't it follow that near surface sea water temps would be also. [b]
Nice thought. Wrong. But a nice thought. The data on temperatures and growth rates were all collected prior to the bleaching events.
Evolutionarily, coral reef biologist consider that coral diversity has always shown peaks where the water temperatures have been in the low to mid 80 ranges.
[b]The temp in Fiji is too cold for the survival of what??? Sure Fiji may not be a the center of maximum diversity, but it is still quite high. [b/]
Wrong. Fiji is a cooler reef with significantly lower diversity than areas of good coral growth. Less than 10 percent of the worlds coral species can survive there.
The coolest tropical coral reefs get down to about 60 deg F. for short periods, and the few species of corals that can take that cold a temperature barely eke out survival. Other cool coral reefs, such as Bermuda and Midway, island have plenty of coral individuals, but they have very poor species diversity.
Our corals do not come from these low temperature areas....