Paper Reviewed
deVries, M.S., Webb, S.J., Tu, J., Cory, E., Morgan, V., Sah, R.L., Deheyn, D.D. and Taylor, J.R.A. 2016. Stress physiology and weapon integrity of intertidal mantis shrimp under future ocean conditions. Scientific Reports 6: 38637, DOI:10.1038/srep38637.

Setting the stage for their study, deVries et al. (2016) write that, "to date, no mantis shrimp, and relatively few crustaceans, have been focal in ocean acidification research." Thus, seeking to remedy this situation, the team of eight U.S. researchers set out to "examine the long-term effects of moderate increases in pCO2 and temperature on mantis shrimp stress physiology, as well as the exoskeleton morphology and mechanical properties of the merus segment of the raptorial appendage as compared to the carapace, which is a less specialized segment of the exoskeleton."

Their work was accomplished in a controlled-environment located at Scripps Institution of Oceanography, University of California, San Diego, CA, where adult mantis shrimp (Neogonodactylus bredini) specimens were subjected to one of three treatments for a period of six months: ambient (pH of 7.88, pCO2 of 636 µatm, and water temperature of 27.4 °C), reduced pH (pH of 7.57, pCO2 of 1335 µatm, and water temperature of 27.2 °C), and reduced pH with elevated temperature (pH of 7.59, pCO2 of 1301 µatm, and water temperature of 29.7 °C). Half way through the experiment and at its conclusion the authors measured several parameters pertaining to the shrimp's growth, physiological stress and exoskeleton morphology. It was their hypothesis that "reduced pH combined with increased temperature would elicit an oxidative stress response in N. bredini as well as an increase in exoskeleton mineralization, yielding a stiffer, harder exoskeleton that would make the raptorial appendage more brittle and less effective."

Was their hypothesis correct?

In a word, no! Contrary to their initial thinking, the mantis shrimp exhibited an "apparently large tolerance range for changes in environmental pH and temperature." More specifically, they found that "N. bredini showed no changes in growth, molting, enzymatic and protein indicators of oxidative stress, exoskeleton morphology, calcium content, or mechanical properties in response to experimental pH and temperature stressors," which findings, in their words, suggest "that this species has evolved compensation mechanisms to cope with significant environmental change." And if this one species has developed compensation mechanisms, it is not an illogical stretch to assume that other intertidal species have done so too.

Commenting on the reason why the mantis shrimp's skeleton did not dissolve in the lower pH treatments, deVries et al. opine that "the epicuticle in crustaceans may serve as a protective layer against changes in external seawater conditions, thereby preventing dissolution (Ries et al., 2009)," adding that "at the same time, crustaceans use acid-base regulation to buffer hemolymph pH from increases in seawater HCO3- so that hemolymph pH, and therefore the availability of HCO3^- for exoskeleton construction in hemolymph, is maintained," citing the works of Wheatley and Henry (1992), Spicer et al. (2007), Pörtner (2008), Melzner et al. (2009), Ries et al. (2009) and Small et al. (2010). Consequently, alarmist concerns for the future well-being of marine life in response to the twin evils of ocean acidification and warming are tempered yet again by observations showing that life tends to find a way to cope with the many challenges it faces.

References
Melzner, F., Gutowska, M.A., Langenbuch, M., Dupont, S., Lucassen, M., Thorndyke, M.C. Bleich, M. and Pörtner, H.-O. 2009. Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny? Biogeosciences Discussions 6: 4693-4738.

Pörtner, H.O. 2008. Ecosystem effects of ocean acidification in times of ocean warming: a physiologist's view. Marine Ecology Progress Series 373: 203-217.

Ries, J.B., Cohen, A.L. and McCorkle, D.C. 2009. Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37: 1131-1134.

Small, D., Calosi, P., White, D., Spicer, J.I. and Widdicombe, S. 2010. Impact of medium-term exposure to CO2 enriched seawater on the physiological functions of the velvet swimming crab Necora puber. Aquatic Biology 10: 11-21.

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Wheatly, M.G. and Henry, R.P. 1992. Extracellular and intracellular acid-base regulation in crustaceans. The Journal of Experimental Zoology 263: 127-142.