How does rising atmospheric CO2 affect marine organisms?

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CO2-Enriched Ecosystems Support Greater Animal Populations
Jones, T.H., Thompson, L.J., Lawton, J.H., Bezemer, T.M., Bardgett, R.D., Blackburn, T.M., Bruce, K.D., Cannon, P.F., Hall, G.S., Hartley, S.E., Howson, G., Jones, C.G., Kampichler, C., Kandeler, E. and Ritchie, D.A.  1998.  Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems.  Science 280: 441-443.

In an article published in the 1995 World Climate Report and entitled "Rising CO2: A Breath of New Life for the Biosphere," Dr. Keith E. Idso stated that "it is abundantly clear that earth's animal life will experience population responses to rising levels of atmospheric CO2 that will parallel those of the plant kingdom; for the greater the food base, the greater the super-structure of life that can be supported."  What seems obvious to one person, however, may not be nearly so clear to another; and the ultimate proof of such a postulate may sometimes reside years, or even decades, in the future.  It is thus immensely gratifying that a mere three years were required to provide a sound experimental demonstration of this "obvious" - but not nearly so easy to demonstrate - consequence of atmospheric CO2 enrichment.

What Was Done
The 15 authors of this paper brought together the expertise of 10 different research institutions scattered throughout the United Kingdom, Austria and the United States to study complex food chain responses to atmospheric CO2 enrichment in model terrestrial ecosystems maintained within the sophisticated Ecotron controlled environment facility at Silkwood Park, Ascot, Berkshire, UK.  Eight microcosms, each covering a ground area of 1 mē, were maintained at the local ambient CO2 concentration, while eight others were maintained at a CO2 concentration approximately 53% greater for a period of nine months.  Throughout this period, numerous ecological parameters were measured.

What was learned
As the plants of the ecosystems went through three complete generations, the CO2-enriched plant communities typically fixed more carbon as a consequence of their enhanced rates of photosynthesis.  Most of the extra production was directed below-ground, where it increased the dissolved organic carbon and nitrogen concentrations of the CO2-enriched microcosms' soil water supplies.  This change, in turn, led to the development of a greater biomass of certain soil fungi in the CO2-enriched ecosystems.  At the end of this food chain were several species of soil microarthropods that fed upon the soil fungi; and the 53% increase in the atmospheric CO2 content of the CO2-enriched microcosms led to a 52% increase in the number of these fungal grazers.

What it means
Ecosystems composed of primary producers, herbivores, carnivores, and decomposers are extremely complex; and it is not always possible to predict what the end result of a change in environmental conditions will mean for such an assemblage of life forms.  In this case, standing plant biomass changed very little in response to an increase in the air's CO2 concentration.  However, the enhanced fixation of carbon in a CO2-enriched ecosystem has to show up somewhere; and in this experiment it appeared in the dissolved organic carbon content of the soil water of the ecosystems exposed to the extra CO2.  This augmented carbon supply then supported a greater soil fungal population, which in turn supported a greater soil microarthropod population, the size of which was enhanced by essentially the same percentage as the percent increase in the airspace CO2 concentration of the CO2-enriched microcosms.

Although CO2-enhanced "carbon trails" are sometimes long and tortuous, if diligently followed, as the one in this case was, they should ultimately lead to some manifestation of enhanced life processes or organismal numbers.  This study provides important evidence for the validity of this postulate.

Reviewed 15 September 1998