Impact of CO2-acidified seawater on the extracellular acid-base balance of the northern sea urchin Strongylocentrotus droebachiensis

We investigated the effect of five day exposure to CO2-acidified sea water treatments (pH(NBS) = 7.89 [control], 7.44, 7.16 and 6.78, T=9.5 degrees C) on the extracellular acid base balance of the northern sea urchin Strongylocentrotus droebachiensis. In each case there was an uncompensated respiratory acidosis which increased in intensity with decreasing environmental pH. This was very similar to results for another sea urchin species, Psammechinus miliaris (8 d exposure, T=15 degrees C). However, there were some important differences in the response to low seawater pH between the two urchin species S. droebachiensis and P. miliaris. At the lowest pH tested (6.78) there was a metabolic component to this acidosis recorded (correlated with a significant increase in L-lactate) in S. droebachiensis but not P. miliaris. The acidosis was accompanied by a very small, but significant increase in coelomic fluid calcium. Also the water used in our study was (controlling for pH) markedly undersaturated with respect to carbonate compared with that used in the Psammechinus study, highlighting the need for the environmental context to be assessed in future comparative studies. (C) 2011 Elsevier B.V. All rights reserved.