How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 and Temperature on Saltmarsh Plants
Reference
Gray, A.J. and Mogg, R.J.  2001.  Climate impacts on pioneer saltmarsh plants.  Climate Research 18: 105-112.

What was done
Two saltmarsh species, the C3 Puccinellia maritima and the C4 Spartina anglica, were grown for eleven months in solardomes (greenhouse-type structures) receiving ambient and elevated (ambient plus 340 ppm) atmospheric CO2 concentrations in combination with ambient and elevated (ambient plus 3°C) air temperatures to determine the interacting effects of these variables on plant growth.  In addition, plants were grown singly and in different proportional combinations with each other to determine if any competitive interactions exist between the two species.

What was learned
In pure stands, elevated CO2 significantly enhanced plant growth, as did elevated temperature, regardless of species.  In such monocultures, the greatest biomass produced by Puccinellia plants occurred in the combined elevated CO2/elevated air temperature treatment.  In contrast, those combined variables actually had no significant impact on the growth of Spartina plants, which increased their biomass equally well in response to either elevated CO2 or elevated air temperature alone.

When grown in competitive mixtures, Puccinellia plants displayed slight reductions in growth due to elevated CO2 or elevated air temperature alone, but exhibited enhanced biomass production in response to these variables when combined.  In contrast, Spartina plants continued to display enhanced growth in response to elevated CO2 or elevated air temperature alone, but exhibited no change in growth (relative to that observed under ambient conditions) when both environmental variables were increased.

What it means
As the atmospheric CO2 concentration increases, these two saltmarsh species will respond differently in monocultures and mixed stands.  In both situations, elevated CO2 will likely enhance the growth of Spartina species, but only if air temperatures do not rise.  Puccinellia plants, on the other hand, will likely respond positively to increases in the air's CO2 content, enhancing their growth even more under simultaneous conditions of increased air temperatures and competition.  In addition, the authors conclude that predicted climate change will likely lead to a "northward development of saltmarshes with lower elevational limits than at present."  As a consequence of these several responses to environmental changes predicted for the future, earth's saltmarshes will likely increase the amount of carbon they sequester.


Reviewed 20 February 2002