How does rising atmospheric CO2 affect marine organisms?

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Effects of Atmospheric CO2 Enrichment on Cuttlefish Eggs and Embryo Development
Lacoue-Labarthe, T., Martin, S., Oberhansli, F., Teyssie, J.-L., Markich, S., Ross, J. and Bustamante, P. 2009. Effects of increased pCO2 and temperature on trace element (Ag, Cd and Zn) bioaccumulation in the eggs of the common cuttlefish, Sepia officinalis. Biogeosciences 6: 2561-2573.

What was done
The authors placed fertilized eggs of the common cuttlefish (Sepia officinalis) within five-liter plastic bottles filled with filtered and UV sterilized Mediterranean seawater pumped from a depth of 30 meters at a site adjacent to Monaco Bay, after which the eggs were maintained throughout their full development time at controlled conditions of temperature (16 or 19C) and pH (8.1, 7.85 or 7.6), the latter of which values were maintained within 0.05 of a pH unit by periodically bubbling pure CO2 into the bottles (which were continuously aerated with CO2-free air), resulting in mean CO2 concentrations of the air in contact with the surface of the water of either 400, 900 or 1400 ppm.

What was learned
Lacoue-Labarthe et al. report that "decreasing pH resulted in higher egg weight at the end of development at both temperatures (p < 0.05), with maximal values at pH 7.85 (1.60 0.21 g and 1.83 0.12 g at 16C and 19C, respectively)." In addition, they found that "hatchlings were smaller when they developed at 16C than at 19C (p < 0.05)." They also observed that zinc (Zn) accumulation "was higher at pH 7.85 during the full developmental period," when "high embryonic requirements for Zn are not fully covered by the maternal pool," so that the higher accumulation of Zn "was associated with a greater rate of growth of both egg and embryo." Concurrently, there was also a greater accumulation of potentially detrimental silver in the tissues of the hatchlings; but any deleterious effects of the extra silver were apparently more than overcome by the positive effects of lowered pH on beneficial zinc accumulation, while toxic cadmium accumulation was actually reduced in the lower pH (or higher CO2) treatments.

What it means
The seven scientists conclude their paper by writing that "decreasing pH until 7.85," such as could be expected to occur in air enriched with carbon dioxide to a concentration of 900 ppm, "should lead to some possibly beneficial effects, such as a larger egg and presumably hatchling size and a better incorporation of the essential element[s] such as Zn in the embryonic tissue," which phenomena, in their words, "may improve the survival [of] the newly hatched juveniles." What is more, they add that Gutowska et al. (2008) have demonstrated that "calcification was enhanced in sub-adult cuttlefish reared at 6,000 ppm CO2." Hence, it would appear that the ongoing rise in the air's CO2 content may well prove providential for cuttlefish.

Gutowska, M.A., Portner, H.O. and Melzner, F. 2008. Growth and calcification in the cephalopod Sepia officinalis under elevated seawater pCO2. Marine Ecology Progress Series 373: 303-309.

Reviewed 9 June 2010