What was done
The authors investigated the effects of ocean acidification state (pH values of 8.2-7.6, corresponding to atmospheric CO2 concentrations of 230-690 ppm) and seawater temperature (20-26°C, where 20°C represents the recent thermal history of indigenous adults) on the fertilization of sea urchin (Heliocidaris erythrogramma) eggs and their subsequent development in what they call "the eastern Australia climate change hot spot," which is located near Sydney.

What was learned
Byrne et al. report that over the ranges of seawater pH and temperature they studied, there was "no effect of pH" and "no interaction between temperature and pH" on sea urchin egg fertilization. In addition, they report that "comparative data on the effect of increased CO2 and decreased pH as a single stressor on sea urchin fertilization and development are available for five species," and that "these studies show that sea urchin fertilization and early development are only affected by pH < 7.4 (above 1000 ppm CO2)," citing the work of Bay et al. (1993), Kurihara and Shirayama (2004) and Carr et al. (2006).

Seawater pH also had no effect on the longer-term development of fertilized sea urchin eggs; but the six scientists say that warming led to "developmental failure at the upper warming (+4 to +6°C) level, regardless of pH." Even here, however, they appear quite hopeful, stating that "it is not known whether gametes from H. erythrogramma adults acclimated to 24°C would have successful development in a +4°C treatment," stating that their study "highlights the potentiality that adaptive phenotypic plasticity may help buffer the negative effects of warming, as suggested for corals." In fact, they note that "single stressor studies of thermotolerance in a diverse suite of tropical and temperate sea urchins show that fertilization and early development are robust to temperature well above ambient and the increases expected from climate change," citing the work of Farmanfarmaian and Giese (1963), Chen and Chen (1992) and Roller and Stickle (1993).

What it means
All things considered, it would appear that sea urchins may be well equipped to deal with the challenges of projected ocean acidification and global warming, and then some, even if they were to occur simultaneously.

References
Bay, S., Burgess, R. and Nacci, D. 1993. Status and applications of echinoid (phylum Echinodermata) toxicity test methods. In: Landis, W.B., Hughes, J.S. and Lewis, M.A., Eds. Environmental Toxicology and Risk Assessment. American Society of Testing and Materials, Philadelphia, Pennsylvania, USA, pp. 281-302.

Carr, R.S., Biedenbach, J.M. and Nipper, M. 2006. Influence of potentially confounding factors on sea urchin porewater toxicity tests. Archives of Environmental Contamination and Toxicology 51: 573-579.

Chen, C.P. and Chen, B.Y. 1992. Effects of high temperature on larval development and metamorphosis of Arachnoides placenta (Echinodermata Echinoidea). Marine Biology 112: 445-449.

Farmanfarmaian, A. and Giese, A.C. 1963. Thermal tolerance and acclimation in the western purple sea urchin, Strongylocentrotus purpuratus. Physiol. Zool. 36: 237-343.

Kurihara, H. and Shirayama, Y. 2004. Effects of increased atmospheric CO2 on sea urchin early development. Marine Ecology Progress Series 274: 161-169.

Roller, R.A. and Stickle, W.B. 1993. Effects of temperature and salinity acclimations of adults on larval survival, physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea). Marine Biology 116: 583-591.