How does rising atmospheric CO2 affect marine organisms?

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Effects of an Order-of-Magnitude Increase in Aquatic CO2 on the Growth of Algae and Macrophytes in a Danish Lake
Andersen, T. and Andersen, F.O. 2006. Effects of CO2 concentration on growth of filamentous algae and Littorella uniflora in a Danish softwater lake. Aquatic Botany 84: 267-271.

What was done
Working with six 1.5-m-diameter flexible plastic cylinders placed in the littoral zone of Lake Hampen in central Jutland, Denmark (three maintained at ambient CO2 and three enriched to ten times the ambient CO2 concentration), the authors documented the CO2-induced growth response of a mixture of several species of filamentous freshwater algae (dominated by Zygnema species, but containing some Mougeotia and Spirogyra), as well as an isoetid community of macrophytes (dominated by Littorella uniflora, but containing some Myriophyllum alterniflorum and a few other species).

What was learned
After one full growing season (May to November), it was determined that the ten-fold increase in aquatic CO2 enhanced the biomass production of Littorella uniflora by approximately 78%. The biomass of filamentous algae was also enhanced by the elevated CO2: by 220% in early July, by 90% in mid-August, and by a whopping 3,750% in mid-November.

What it means
Huge increases in aquatic CO2 concentration can lead to equally huge increases in the growth of filamentous freshwater algae and various aquatic macrophytes, even though the massive filamentous algal growth may greatly decrease the light available to the macrophytes growing beneath them, as was the case in this study.

Reviewed 5 July 2006