How does rising atmospheric CO2 affect marine organisms?

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Effects of CO2 and O2 Concentrations on a Seaweed
Kubler, J.E., Johnston, A.M. and Raven, J.A.  1999.  The effects of reduced and elevated CO2 and O2 on the seaweed Lomentaria articulataPlant, Cell and Environment 22: 1303-1310.

What was done
A red seaweed common to the Northeast Atlantic intertidal zone, Lomentaria articulata, was grown for three weeks in hydroponic cultures subjected to various atmospheric CO2 and O2 concentrations to determine the effects of these gases on growth.

What was learned
Oxygen concentrations ranging between 10 and 200% of ambient had no significant effects on daily net carbon gain or total wet biomass production rates in this seaweed.  In contrast, CO2 concentrations ranging between 67 and 500% of ambient had highly significant effects these parameters.  At twice the current ambient CO2 concentration, for example, daily net carbon gain and total wet biomass production rates were 52 and 314% greater than they were under ambient CO2 conditions.  Even though this seaweed was likely carbon saturated, when grown at five-times the ambient CO2 concentration, it still exhibited daily net carbon gain and wet biomass production rates that were 23 and 50%, respectively, greater than those of control plants.

What it means
As the CO2 content of the air rises, it is likely that aquatic plants, such as this red seaweed, will exhibit increases in photosynthesis and growth, just as nearly all terrestrial plants do.  Thus, in the future, aquatic plants will likely increase their productivity and consequently stimulate the various food webs they help support.

Reviewed 1 June 2000