How does rising atmospheric CO2 affect marine organisms?

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Effects of Ultra-High Atmospheric CO2 Concentrations on the Growth of Three Laminaceae Species
Tisserat, B.  2001.  Influence of ultra-high carbon dioxide concentrations on growth and morphogenesis of Lamiaceae species in soil.  Journal of Herbs, Spices & Medicinal Plants 9: 81-89.

Whether a substance is helpful or harmful to an organism is highly dependent on its dosage and, therefore, on the concentration of the substance within the matrix that delivers it to the organism, such as food and water that is ingested or air that is inhaled.  Within this context, it is often opined that ultra-high atmospheric CO2 concentrations may be harmful to plants; but there is little research to support this opinion.  In fact, many studies, such as the one reviewed here, suggest just the opposite.

What was done
The author grew spearmint (Mentha spicata L.), water mint (Mentha aquatica L.) and thyme (Thymus vulgaris L.) plants for a period of four weeks in containers of soil housed within greenhouse compartments maintained at atmospheric CO2 concentrations that ranged from 350 to 10,000 ppm, after which he measured the plants' final fresh weights.

What was learned
Compared to thyme plants grown in air of 350 ppm CO2, thyme plants grown in air of 3,000 ppm CO2 produced 160% more fresh weight.  Likewise, the fresh weights of spearmint and water mint plants rose by 150% and 220%, respectively, when grown at an atmospheric CO2 concentration of 10,000 ppm as opposed to a concentration of 350 ppm.

What it means
Increases in atmospheric CO2 concentration that are greater than anything that could realistically be conceived to occur as a consequence of anthropogenic CO2 emissions not only do not appear to be detrimental to the three plants investigated in this study, they appear to be highly beneficial.

Reviewed 10 August 2005