How does rising atmospheric CO2 affect marine organisms?

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Larval & Post-Larval Responses of Pacific Oysters to Elevated CO2
Ginger, K.W.K., Vera, C.B.S., Dineshram, R., Dennis, C.K.S., Adela, L.J., Yu, Z. and Thiyagarajan, V. 2013. Larval and post-larval stages of Pacific oyster (Crassostrea gigas) are resistant to elevated CO2. PLoS ONE 8: e64147.

The authors write that it is widely believed that" human-caused pH change is posing serious threats and challenges to the pacific oyster (Crassostrea gigas), especially to their larval states." However, they note that "our knowledge of the effect of reduced pH on C. gigas larvae presently relies presumptively on four short-term (< 4 days) survival and growth studies." And they clearly feel that this paucity of experimental data is insufficient to draw such strong conclusions.

What was done
Based on multiple physiological measurements made during various life stages of the oysters, Ginger et al. studied "the effects of long-term (40 days) exposure to pH 8.1, 7.7 and 7.4 on larval shell growth, metamorphosis, respiration and filtration rates at the time of metamorphosis, as well as the juvenile shell growth and structure of C. gigas.

What was learned
The seven scientists discovered that (1) "mean survival and growth rates were not affected by pH," that (2) "the metabolic, feeding and metamorphosis rates of pediveliger larvae were similar, between pH 8.1 and 7.7," that (3) "the pediveligers at pH 7.4 showed reduced weight-specific metabolic and filtration rates, yet were able to sustain a more rapid post-settlement growth rate," and that (4) "no evidence suggested that low pH treatments resulted in alterations to the shell ultra-structures or elemental compositions (i.e., Mg/Ca and Sr/Ca ratios)."

What it means
In light of these several positive findings, Ginger et al. concluded that "larval and post-larval forms of the C. gigas in the Yellow Sea are probably resistant to elevated CO2 and decreased near-future pH scenarios." In fact, they opine that "the pre-adapted ability to resist a wide range of decreased pH may provide C. gigas with the necessary tolerance to withstand rapid pH changes over the coming century."

Reviewed 16 October 2013