Back to the Great Barrier Reef (GBR) and why a flying inspection of coral is fairly useless unless your a modern so-called coral 'research' scientist who's just out to get the taxpayer to fund your flying jolly's...
Via, Studies on the Physiology of Corals. Younge and Nicholls. (on the GBR near Cairns)
"...When walking over the exposed reef flat during the next spring tides on March 21st, (year 1929) great numbers of whitened skeletons of corals killed by the great heat a month previously, were seen. In addition there were a number of other corals, principally species of Favia and Goniastrea, which were equally white, but which, on closer examination, were found to be alive and perfectly healthy, but with colourless, transparent tissues..."
Note - Before the eco-loons jump in, in other research, Younge and Nicholls also comment on same species coral in mild weather unaffected by heat stress having colour ranges from translucent through to brown within metres of each other.
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