Background
The authors write that "the reproductive processes and early life-stages of both calcifying and non-calcifying animals are believed to be particularly vulnerable to a reduced pH environment," but they say "there is as yet no clear and reliable predictor for the impacts of ocean acidification on marine animal reproduction."

What was done
As their contribution to the scientific quest for this important knowledge, Caldwell et al. say they "investigated the combined effect of pH (8.06-7.67) and temperature (14-20°C) on percent sperm motility and swimming speed in the sea urchin Psammechinus miliaris using computer assisted sperm analysis (CASA)," while working with specimens they collected from the Isle of Cumbrae (Scotland).

What was learned
"Surprisingly," in the words of the six scientists, "sperm swimming performance benefited greatly from a reduced pH environment," as "both percent motility and swimming speeds were significantly enhanced at pHs below current levels." And in light of the additional fact that sperm-activating peptides - which are believed to have evolved some 70 million years ago during a period of high atmospheric CO2 concentration - are fully functional from pH 6.6 to 8.0 (Hirohashi and Vacquier, 2002), they state that "the combined data on motility, swimming speed and SAP function at reduced pH indicates that sperm are sufficiently robust to allow functionality at pHs that would have been experienced in the paleo-ocean (ca pH 7.4-7.6) and which are within projections for near-future climate change scenarios."

What it means
The UK researchers conclude that "current ocean pH levels are suboptimal for P. miliaris sperm-swimming speed and that reproductive success for certain marine species may benefit from a reduced pH ocean."

Reference
Hirohashi, N. and Vacquier, V.D. 2002. Egg fucose polymer, sialoglycan, and speract all trigger the sea urchin sperm acrosome reaction. Biochemical and Biophysical Research Communications 296: 833-839.