How does rising atmospheric CO2 affect marine organisms?

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Arthropods -- Summary
How will ecosystem populations of animals that reside at the ends of various food chains be affected by atmospheric CO2 enrichment?  If the productivity of the plants at the base of a food chain is enhanced by the aerial fertilization effect of extra CO2, one would expect that greater animal populations would be supported at the other end.  But is this expectation correct?

In an experiment that begins to answer this question, Siemann (1998) studied the effects of both short- and long-term nitrogen fertilization on plant productivity and arthropod communities in an upland grass ecosystem in Minnesota.  In both situations, plant productivity was enhanced; and arthropods responded by increasing both their numbers and the number of their species, suggesting that if atmospheric CO2 enrichment tended to enhance plant productivity, it too would increase arthropod numbers and ecosystem species richness.  But is this supposition correct?

Rillig et al. (1999) determined that it is.  In serpentine and sandstone grasslands in California, they found that an approximate doubling of the air's CO2 content significantly enhanced the masses of fungi living in the soil, resulting in large increases in the numbers of fungal-feeding microarthropods (108 and 39% increases in the sandstone and serpentine grasslands, respectively).  Likewise, in a study of well-fertilized poplar tree cuttings in Michigan, Lussenhop et al. (1998) observed that the fine roots of the trees in their approximately-doubled-CO2 treatment supported twice as many microarthropods as the fine roots of the trees growing in ambient air.  Finally, in a multiple-microcosm study of mini-terrestrial ecosystems conducted in the United Kingdom, Jones et al. (1998) found that a 53% increase in atmospheric CO2 concentration produced an enhanced soil fungal population that supported 52% more soil microarthropods.

In conclusion, as simple reason suggests, enhanced plant productivity, driven by elevated levels of atmospheric CO2, does indeed tend to support greater animal populations at the ends of various food chains ... at least in the case of soil microarthropods.  Further application of simple reason suggests that the same should also hold true for other animal species.

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.

Lussenhop, J., Treonis, A., Curtis, P.S., Teeri, J.A. and Vogel, C.S.  1998.  Response of soil biota to elevated atmospheric CO2 in poplar model systems.  Oecologia 113: 247-251.

Rillig, M.C., Field, C.B. and Allen, M.F.  1999.  Soil biota responses to long-term atmospheric CO2 enrichment in two California annual grasslands.  Oecologia 119: 572-577.

Siemann, E.  1998.  Experimental tests of effects of plant productivity and diversity on grassland arthropod diversity.  Ecology 79: 2057-2070.