How does rising atmospheric CO2 affect marine organisms?

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Assessing the Future of Earth's Coral Reefs
Idso, S.B., Idso, C.D. and Idso, K.E.  2000.  CO2, global warming and coral reefs: Prospects for the future.  Technology 7S: 71-94.

A disturbing perturbation of earth's biosphere that has become increasingly pronounced over the past two decades is the phenomenon of coral bleaching, whereby photosynthetic algae that live in close association with coral polyps are periodically expelled from their hosts, oftentimes leading to the demise of the coral polyps and the degradation of the highly diverse and productive reef ecosystems that have been gradually built up over the centuries by this important symbiotic association.  Because of the fact that global temperatures are believed to have risen over this same time period, it has been postulated that thermal stresses have been responsible for the increasing frequency of bleaching episodes.  It has also been postulated that the increasing concentration of atmospheric CO2 is altering the carbonate chemistry of seawater in such a way as to reduce coral calcification rates, and that the combined effects of both of these phenomena may well spell serious trouble for the planet's coral reefs in just a few short years.

What was done
The authors reviewed a voluminous body of literature relative to the ongoing rise in the air's CO2 content as it pertains to the future health of earth's coral reefs.

What was learned
It was found that highly publicized claims of global warming and rising atmospheric CO2 concentrations being inimical to earth's coral reefs have been generally oversimplified, often exaggerated, and sometimes even misinterpreted.  The scientific literature reveals, for example, that (1) there is no simple linkage between high water temperatures and coral bleaching, (2) bleaching may, in fact, be an adaptive mechanism that helps corals survive increasing temperatures, (3) reefs will likely benefit from the rising sea levels thought to result from global warming, and (4) atmospheric CO2 enrichment may actually enhance coral calcification rates.

What it means
The scientific community is clearly not united on the subject of atmospheric CO2 enrichment and coral reef health.  In spite of this diversity of thought, however, there is agreement on one aspect of the problem, and that is that local anthropogenic influences can severely weaken coral reefs, making them more susceptible to changes in the global environment they have tolerated quite well in the past.  Consequently, well-thought-out local solutions to well-defined local problems may well do more to protect earth's coral reefs from pervasive environmental changes than anything anyone could ever do in the global arena.

Reviewed 6 September 2000