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Water Quality and Warming-Induced Coral Bleaching
Volume 12, Number 39: 30 September 2009

In a Journal Review published in CO2 Science on 1 Oct 2003, to which we gave the title The Increasing Sensitivity of Corals to Rising Temperatures, we noted we had long suggested that the intensification of a host of widespread but localized anthropogenic-induced stresses was predisposing the world's corals to more readily succumb to the stress of rising temperatures, citing our Editorials of 23 Jan 2002, 6 Mar 2002 and 26 Mar 2003, while stating that "the insidious worldwide increase in a host of localized anthropogenic assaults upon reef environments over the course of the Industrial Revolution has gradually weakened corals to the point where they now succumb to increases in temperature that in the past would not have affected them." In what follows, we briefly describe the recent findings of Wooldridge (2009), which provide compelling new evidence that our early assessment of the situation was indeed correct.

The Australian Institute of Marine Science researcher begins by noting that Berkelmans (2002) documented regional-scale differences in bleaching susceptibility to short-term (3-5 days) extreme heat events throughout the Great Barrier Reef (GBR), and that "adoption of the regional thresholds as an early warning system on the GBR has confirmed their accuracy through multiple bleaching events (Berkelmans, 2008)." From this starting point, he goes on to demonstrate there is a quantitative linkage "between terrestrially-sourced dissolved inorganic nitrogen (DIN) loading" -- which "is typically highest at coastal locations that are exposed to terrestrial runoff" -- "and the upper thermal bleaching thresholds of inshore reefs on the GBR," and he states that "this biophysical linkage provides concrete evidence for the oft-expressed belief that improved coral reef management will increase the regional-scale survival prospects of coral reefs to global climate change." In fact, he reports that "for inshore reef areas with a high runoff exposure risk, it is shown that the potential benefit of this 'local' management imperative is equivalent to ~2.0-2.5C in relation to the upper thermal bleaching limit."

On the basis of this set of real-world observations, Wooldridge concludes that "a major water quality program effective in reducing ambient DIN loadings could decrease bleaching probability across the whole range of temperatures predicted for the inshore GBR by 2100," noting that "regional-scale reductions in ambient DIN loads are amenable to management, and therefore represent a rational strategy for ameliorating climate change effects on coral reefs," as opposed, we would say, to the irrational strategy of reducing anthropogenic CO2 emissions to the ridiculously low levels currently being proposed by the world's climate alarmists, especially when higher atmospheric CO2 concentrations will be needed to boost future crop water use efficiencies to the levels required to feed the world's burgeoning human population but a few short decades from now, without our taking from what we could call "wild nature" all remaining freshwater and arable land on the face of the planet to produce the crops that will be required just to sustain our species (see, in this regard, many of the items we have archived under the heading of Food in our Subject Index).

Sherwood, Keith and Craig Idso

Berkelmans, R. 2002. Time-integrated thermal bleaching thresholds of reefs and their variation on the Great Barrier Reef. Marine Ecology Progress Series 229: 73-82.

Berkelmans, R. 2008. Bleaching and mortality thresholds: how much is too much? In: van Oppen, M.J.H. and Lough, J.M., Eds., Coral Bleaching: Patterns, Processes, Causes and Consequences. Ecological Studies, Springer.

Wooldridge, S.A. 2009. Water quality and coral bleaching thresholds: Formalizing the linkage for the inshore reefs of the Great Barrier Reef, Australia. Marine Pollution Bulletin 58: 745-751.