Volume 15, Number 35: 29 August 2012
In the intriguing report of their study of the early development of the Mediterranean sea urchin Paracentrotus lividus, Martin et al. (2011) write that "although embryos and larvae are well prepared for environmental changes (Hamdoun and Epel, 2007), it is widely accepted that early life-history stages are more sensitive than adults to ocean acidification." However, they say that this too-rapidly-accepted belief has typically been derived from comparisons made between organisms raised in seawater of current ambient pH and CO2-lowered pH "at one time point and may be partially explained by a delay in the development classically observed under low pH conditions," citing the work of Portner et al. (2010).
As an example of this phenomenon, the eleven researchers write that in their experiment, larvae of P. lividus "collected at pH 7.5 at 46 hours post-fertilization (real age) were smaller than in the control treatment [pH 8.1] and corresponded to a virtual age of 36 hours (a delay in development of 10 hours)." In fact, they state that "down to a pH of 7.25, the larvae at Day 3 have a normal morphology but are delayed in development," such that the apparent decrease in calcification at that point in time is, as they put it, "simply an indirect consequence of the impact of low pH on developmental rate." Or in other words, as they continue, "at a given developmental state (or size), larvae present the same calcium incorporation rate regardless of pH."
One of the major take-home messages of Martin et al.'s study is the demonstrable fact that, as they put it, "the only significant effect of pH was a delay in development," such that "it takes more time and probably more energy (as suggested by the up to 20-fold increase in gene upregulation) to reach the same developmental stage." But reach it the sea urchin do, given just a bit more time, which further implies that scientists that compare various organismal functions at identical times post fertilization, and that discover deficiencies in the performance of those life-sustaining functions by the group of organisms maintained in seawater of lower-than-ambient pH, are not justified in claiming lower performance levels of the studied species in that pH treatment; for given a few more hours or days, as the species involved may require, their performance of the monitored activity may be essentially identical to that of individuals of the same species at the same point of development.
And so it is that the oft-repeated claim that "early life-history stages are more sensitive than adults to ocean acidification" has come to be widely accepted, but erroneously so in perhaps the bulk of the situations investigated.
Sherwood, Keith and Craig Idso
References
Hamdoun, A. and Epel, D. 2007. Embryo stability and vulnerability in an always changing world. Proceedings of the National Academy of Sciences USA 104: 1745-1750.
Martin, S., Richier, S., Pedrotti, M.-L., Dupont, S., Castejon, C., Gerakis, Y., Kerros, M.-E., Oberhansli, F., Teyssie, J.-L., Jeffree, R. and Gattuso, J.-P. 2011. Early development and molecular plasticity in the Mediterranean sea urchin Paracentrotus lividus exposed to CO2-driven acidification. The Journal of Experimental Biology 214: 1357-1368.
Protner, H.O., Dupont, S., Melzner, F. and Thorndyke, M. 2010. Laboratory experiments and benthic mesocosm studies. In: Riebesell, U., Fabry, V.J., Hansson, L. and Gattuso, J.-P. (Eds.). Acidification Research and Data Reporting. Publications Office of the European Union, Luxembourg, pp. 167-180.