How does rising atmospheric CO2 affect marine organisms?

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The Fate of Juvenile Sea Stars in an "Acidified" Ocean
Dupont, S., Lundve, B. and Thorndyke, M. 2010. Near future ocean acidification increases growth rate of the lecithotrophic larvae and juveniles of the sea star Crossaster papposus. Journal of Experimental Zoology (Molecular and Developmental Evolution) 314B: 382-389.

The authors write that "echinoderms are among the most abundant and ecologically successful groups of marine animals (Micael et al., 2009), and are one of the key marine groups most likely to be impacted by predicted climate change events," presumably because "the larvae and/or adults of many species from this phylum form skeletal rods, plates, test, teeth, and spines from an amorphous calcite crystal precursor, magnesium calcite, which is 30 times more soluble than normal calcite (Politi et al., 2004)," and this fact would normally be thought to make it much more difficult for them (relative to most other calcifying organisms) to produce calcification-dependent body parts.

What was done
Working with naturally-fertilized eggs of the common sea star Crossaster papposus, which they collected and transferred to five-liter culture aquariums filled with filtered seawater (a third of which was replaced every four days), Dupont et al. regulated the pH of the tanks to values of either 8.1 or 7.7 by adjusting environmental CO2 levels to either 372 ppm or 930 ppm, during which time they documented (1) settlement success as the percentage of initially free-swimming larvae that affixed themselves to the aquarium walls, (2) larval length at various time intervals, and (3) degree of calcification.

What was learned
The three researchers report that just the opposite of what is often predicted actually happened, as the echinoderm larvae and juveniles were "positively impacted by ocean acidification." More specifically, they found that "larvae and juveniles raised at low pH grow and develop faster, with no negative effect on survival or skeletogenesis within the time frame of the experiment (38 days)." In fact, they state that the sea stars' growth rates were "two times higher" in the acidified seawater; and they remark that "C. papposus seem to be not only more than simply resistant to ocean acidification, but are also performing better."

What it means
The Swedish scientists conclude that "in the future ocean, the direct impact of ocean acidification on growth and development potentially will produce an increase in C. papposus reproductive success," and that "a decrease in developmental time will be associated with a shorter pelagic period with a higher proportion of eggs reaching settlement," leading the sea stars to become "better competitors in an unpredictable environment." Not bad ... especially for a creature that makes its skeletal rods, plates, test, teeth, and spines from a substance that is 30 times more soluble than normal calcite.

Micael, J., Alves, M.J., Costa, A.C. and Jones, M.B. 2009. Exploitation and conservation of echinoderms. Oceanography and Marine Biology 47: 191-208.

Politi, Y., Arod, T., Klein, E., Weiner, S. and Addadi, L. 2004. Sea urchin spine calcite forms via a transient amorphous calcite carbonate phase. Science 306: 1161-1164.

Reviewed 25 August 2010