Since Richard has failed to respond I figured I would throw in my final 2 cents with a few other quotes that are relevent as well as maybe a train of thought for this.
"Biogeography, as a topic for discourse or discussion, is in some ways like religion: both topics lend themselves to ever more complicated treatment in the abstract. which is apt to border even on the miraculous, but which is apt to crumble in confrontation with concrete facts of life." ~ Nelson and Platnick
Sooner or later you are going to have to come to grip with the concrete facts that corals exist where they are able to survive. Some survive in 78F water, but the vast majority survive in 82-84F water. There is nothing to be proud or ashamed of, it is just the way that is....look to nature for the clues my man...they are there.
"There is a clear correlation between generic contours of diversity (isopangeneric contours) and sea surface temperatue" Stehli and Wells 1971
"....they show that species can be widely distributed, that they have continuous ranges from the tropics to high latitudes, that they do not replace one another along these sequences, and that species diversity attenuates in a manner correlated with sea surface temperatue." Veron on a study done by Yabe and Sugiyama in 1935
"The major features of coral distribution are latitudinal and are primarily controlled by temperatue and climate; regional features are primarily longitudinal and are due to geo-tectonic events. enhanced by glacio-eustatic change concentrating speciation in outlying islands" (Rosen 1984)
"Latitudinal limits are ultimately determined by temperature..." Veron pg. 57
"Physical-environmental parameters that generate biogeographic patterns. tend to be either latitude-correlated (including temperature, light, reef/non-reef habitats and boundary currents), or non-latitude-correlated (including non-boundary sea surface circulation, substrate availability, water quality and nutrients, regional ecology and regional dispersion barriers" Veron pg. 89 ~ This goes directly to what I mentioned earlier about trying to combine general biodiversity with regional factors, they are seperate entities but both part of the whole.
And finally a phrase that as soon as I read it made me think of Dr. Ron's article and past discussions...
"Upstream sources continually supply propagules to downstream locations where they survive, or not, according to ecolgical and environmental factors, of which temperature is the most important." Veron pg. 99 ~If that is not almost verbatum of what Dr. Ron has been trying to get across for the past few years I do not know what is. If you want to know the underlying reason that Fiji has 300-400 fewer species than the center of diversity then that is it in a nutshell.
If anyone is wondering why would I defend this so strongly....I can give you one reason and that is when I first read Dr. Ron's stuff I figured he just had to be on drugs (he is from Montana after all..what does that have to do with reefs?)
So I decided to look at whatever I could find that dealt with the subject matter and low and behold it was all there in black and white. He is not some crazy mis-fit from Montana spewing some wild ideas (although apparently there are still some that think this
) but is giving us some common information that apparently has been around since the 1930s...go figure. If I have not said it enough before... "Thanks Dr. Ron!".
Lastly, I was looking through Corals of the World tonight and I can find no better illustration of the effects of temperature on diversity than in Vol. 3 pg. 412 on map #3. If you look at the center of diversity and then trace it north to Japan...this is where the Kuroshio Current runs. It is the fastest and most powerful warm water current in the entire region and starts at the center of diversity region that has "581" stamped on it and heads northward. Look at what happens within just a few degrees from the equator...species drop from 581 to 300 ish. Continue to trace it north until it hits mainland Japan and is slowed and the water is allowed to cool...what happens to species diversity? You betcha, it drops to the 50's and quickly to zero beyond that. What else will it take to prove a point? Really!