How does rising atmospheric CO2 affect marine organisms?

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Elevated CO2 Thwarts Thermal Death of a Floating Aquatic Plant
Reference
Idso, S.B., Allen, S.G., Anderson, M.G. and Kimball, B.A. 1989. Atmospheric CO2 enrichment enhances survival of Azolla at high temperatures. Environmental and Experimental Botany 29: 337-341.

What was done
In a study designed to reveal the effects of high, but normally-occurring, mid-summer air temperatures in Phoenix, Arizona (USA) on the growth of the free-floating aquatic fern Azolla pinnata, the researchers conducted three separate two- to three-month experiments wherein they grew batches of the floating fern in adequately-fertilized water contained in sunken metal stock tanks located within clear-plastic-wall open-top chambers that were continuously maintained at atmospheric CO2 concentrations of either 340 or 640 ppm, during which time the plants were briefly removed from the water and weighed at weekly intervals, while their photosynthetic rates were measured at hourly intervals from dawn to dusk on selected cloudless days.

What was learned
Idso et al. report that the photosynthetic and growth rates of the plants growing in ambient air "first decreased, then stagnated, and finally became negative when the mean air temperature rose above 30°C." In the high CO2 treatment, on the other hand, they found that "the debilitating effects of high temperatures were reduced: in one case to a much less severe negative growth rate, in another case to merely a short period of zero growth rate, and in a third case to no discernible ill effects whatsoever - in spite of the fact that the ambient treatment plants in this instance all died."

What it means
"With the double verification of this phenomenon provided by both weekly biomass and periodic net photosynthesis determinations," the four researchers concluded that "atmospheric CO2 enrichment may be capable of preventing the deaths of some plant species in situations where their demise is normally brought about by either the direct effects of unduly high temperatures or by associated debilitating diseases." Consequently, it is clear that in trying to determine how plants will respond to higher temperatures in a CO2-enriched world of the future, old concepts that do not include phenomena (either known or unknown) related to the positive effects of elevated CO2 on plant physiological processes will likely present an unduly pessimistic picture of what to expect.

Reviewed 4 October 2006