How does rising atmospheric CO2 affect marine organisms?

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Ocean Acidification's Impact on Coral Bleaching: How Great Is It?
Wall, C.B., Fan, T.-Y. and Edmunds, P.J. 2014. Ocean acidification has no effect on thermal bleaching in the coral Seriatopora caliendrum. Coral Reefs 33: 119-130.

The authors write that the effects of ocean acidification (OA) "have received considerable attention," but they say that its "effects on photosynthesis of Symbiodinium within corals remain unclear." And, therefore, they decided "to test whether elevated pCO2 affects bleaching in corals."

What was done
Determined to discover "whether elevated pCO2 predicted for the year 2100 (85.1 Pa) affects bleaching in the coral Seriatopora caliendrum either independently or interactively with high temperature," Wall et al. collected specimens of the species from Nanwan Bay, Taiwan, and subjected them to combinations of temperature (27.7 vs. 30.5°C) and pCO2 (45.1 vs. 85.1 Pa) for 14 days," while assessing all pertinent biological responses of the coral.

What was learned
The three researchers report that "high temperature reduced values of all dependent variables (i.e., bleaching occurred), but high pCO2 did not affect Symbiodinium photophysiology or productivity, and did not cause bleaching," either "individually, or interactively with high temperature."

What it means
As regards coral bleaching, in the words of Wall et al., "the present results clearly support a null effect for high pCO2." Or as they state in the final sentence of their paper's abstract, "short-term exposure to 81.5 Pa pCO2, alone and in combination with elevated temperature, does not cause or affect coral bleaching."

Reviewed 7 May 2014