How does rising atmospheric CO2 affect marine organisms?

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CO2 Effects on a Seaweed of Economic, Health and Environmental Importance
Reference
Zou, D. 2005. Effects of elevated atmospheric CO2 on growth, photosynthesis and nitrogen metabolism in the economic brown seaweed, Hizikia fusiforme (Sargassaceae, Phaeophyta). Aquaculture 250: 726-735.

What was done
The author collected specimens of a brown seaweed (Hizikia fusiforme (Harv.) Okamura) from intertidal rocks along the coast of Nanao Island, Shantou, China, and maintained them in glass aquariums in filtered natural seawater enriched with 60 ÁM NaNO3 and 6.0 ÁM NaH2PO4, where they were continuously aerated with either ambient air of 360 ppm CO2 or CO2-enriched air of 700 ppm CO2. Under these conditions he measured their relative growth and nitrogen assimilation rates, as well as their nitrate reductase activities.

What was learned
The slightly less than a doubling of the air's CO2 concentration increased the seaweed's mean relative growth rate by about 50%, its mean rate of nitrate uptake during the study's 12-hour light periods by some 200%, and its nitrate reductase activity by approximately 20% over a wide range of substrate nitrate concentrations.

What it means
With respect to human health, Zou notes that "the extract of H. fusiforme has an immunomodulating activity on humans and this ability might be used for clinical application to treat several diseases such as tumors (Suetsuna, 1998; Shan et al., 1999)." He also reports that the alga "has been used as a food delicacy and an herbal ingredient in China, Japan and Korea." In fact, he says that it "is now becoming one of the most important species for seaweed mariculture in China, owing to its high commercial value and increasing market demand." As a result, the ongoing rise in the air's CO2 content bodes well for all of these applications. In addition, Zou notes that "the intensive cultivation of H. fusiforme would remove nutrients more efficiently with the future elevation of CO2 levels in seawater, which could be a possible solution to the problem of ongoing coastal eutrophication," suggesting that rising CO2 levels may also assist in the amelioration of this environmental problem.

References
Shan, B.E., Yoshida, Y., Kuroda, E. and Yamashita, U. 1999. Immunomodulating activity of seaweed extract on human lymphocytes in vitro. International Journal of Immunopharmacology 21: 59-70.

Suetsuna, K. 1998. Separation and identification of angiotensin I-converting enzyme inhibitory peptides from peptic digest of Hizikia fusiformis protein. Nippon Suisan Gakkaishi 64: 862-866.

Reviewed 5 April 2006