What was done
Embryos of the sea urchin Tripneustes gratilla were reared in flow-through chambers filled with filtered seawater maintained at all combinations of three different temperatures (24, 27 and 30°C) and three different pH values (8.15, 7.8 and 7.6), where the 24°C/pH 8.15 combination represented normal control conditions. Then, after five days of such exposure, the growth and development of the larvae were assessed.

What was learned
Brennand et al. report that "larvae reared at pH 7.6 and pH 7.8 had smaller post oral arms when compared with those reared at control pH." However, they report that "a +3°C warming diminished the negative effects of low pH/high CO2," as was "seen in the similar post oral arm length of larvae treated at 27°C/pH 7.6 and 27°C/pH 7.8 and those reared in control temperature and pH." In addition, they say that "as total length of calcite rods is largely comprised of the post oral arms, this measure [of calcification] followed a similar pattern."

What it means
The results of this study suggest that the negative effects of a 0.35 to 0.55 CO2-induced decline in seawater pH on the growth and calcification of the sea urchin Tripneustes gratilla can be largely overcome by a 3°C increase in water temperature. And since the analysis of Tans (2009) -- as discussed in our review of the study of Lombard et al. (2010) -- suggests that the maximum decline in seawater pH that will likely ever be produced by the burning of fossil fuels will be somewhere in the range of only 0.1 to 0.18 in the vicinity of AD 2100 (after which pH begins to slowly rebound), there would seem to be little reason for concern about any negative impact of rising atmospheric CO2 concentrations on this particular species of sea urchin, which is widely distributed throughout the Indo-Pacific region and is well suited for production by aquaculture (Lawrence and Agatsuma, 2007; Juinio-Menez et al., 1998; Dworjanyn et al. 2007).

References
Dworjanyn, S.A., Pirozzi, I. and Liu, W. 2007. The effect of the addition of algae feeding stimulants to artificial diets for the sea urchin Tripneustes gratilla. Aquaculture 273: 624-633.

Juinio-Menez, M.A., Macawaris, N. and Bangi, H. 1998. Community-based sea urchin (Tripnuestes gratilla) grow-out culture as a resource management tool. Canadian Special Publication of Fisheries and Aquatic Science 125: 393-399.

Lawrence, J.M. and Agatsuma, Y. 2007. Ecology of Tripneustes. In: Lawrence, J.M. (Ed.) The Biology and Ecology of Edible Urchins. Elsevier Science, Amsterdam, The Netherlands, pp. 499-520.

Lombard, F., da Rocha, R.E., Bijma, J. and Gattuso, J.-P. 2010. Effect of carbonate ion concentration and irradiance on calcification in planktonic foraminifera. Biogeosciences 7: 247-255.

Tans, P. 2009. An accounting of the observed increase in oceanic and atmospheric CO2 and an outlook for the future. Oceanography 22: 26-35.