How does rising atmospheric CO2 affect marine organisms?

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Marine Tubeworms in a CO2-Enriched and Warmer World
Chan, V.B.S., Thiyagarajan, V., Lu, X.W., Zhang, T. and Shih, K. 2013. Temperature dependent effects of elevated CO2 on shell composition and mechanical properties of Hydroides elegans: Insights from a multiple stressor experiment. PLOS ONE 8: e78945.

The authors write that "the majority of marine benthic invertebrates protect themselves from predators by producing calcareous tubes or shells that have remarkable mechanical strength," but they indicate that "an elevation of CO2 or a decrease in pH in the environment can reduce intracellular pH at the site of calcification and thus interfere with the animal's ability to accrete CaCO3," which "may result in the animal producing severely damaged and mechanically weak tubes."

What was done
In light of these concerns, Chan et al. investigated how the interaction of environmental drivers affects the production of calcareous tubes by the serpulid tubeworm, Hydroides elegans, in a factorial manipulative experiment where they analyzed the effects of pH (8.1 and 7.8), salinity (34 and 27‰), and temperature (23 and 29°C) on the biomineral composition, ultrastructure and mechanical properties of the tubeworm's tubes.

What was learned
The five researchers found that "at an elevated temperature of 29°C, the tube calcite/aragonite ratio and Mg/Ca ratio were both increased, the Sr/Ca ratio was decreased, and the amorphous CaCO3 content was reduced." And "notably," as they emphasized, they found that at elevated temperature with decreased pH and reduced salinity, "the constructed tubes had a more compact ultrastructure with enhanced hardness and elasticity compared to decreased pH at ambient temperature."

What it means
As for what these findings suggest about the future, Chan et al. concluded that their "results from the analyses of tube mineralogy, ultrastructure and mechanical properties showed that predicted coastal warming may not hinder H. elegans ability to build normal tubes even in the face of projected near-future decreases in pH or salinity."

Reviewed 5 February 2014