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Observed Tolerance of Juvenile Blue Crabs to Ocean Acidification

Paper Reviewed
Glandon, H.L. and Miller, T.J. 2017. No effect of high pCO2 on juvenile blue crab, Callinectes sapidus, growth and consumption despite positive responses to concurrent warming. ICES Journal of Marine Science 74: 1201-1209.

Within Chesapeake Bay, the blue crab (Callinectes sapidus) plays an integral role in the food web as both predator and prey. However, despite its relevance to the ecosystem, much remains to be learned about this species' response to projected changes in ocean acidification and seawater warming. And recognizing this data void, Glandon and Miller (2017) set out to remedy this situation.

In working to accomplish their objective, the two scientists from the Chesapeake Biological Laboratory of the University of Maryland exposed juvenile blue crab specimens to one of four temperature/pCO2 treatments over two complete molting periods. Temperature values selected for analysis included 26°C (ambient) and 32°C (elevated), the latter of which represents a value at or beyond the upper end of most projections for the end of the century. For pCO2, the ambient value selected was 800 µatm, which is not uncommon for the estuary, whereas the enriched value was selected to be ten times the ambient amount (8,000 µatm), which pCO2 treatment, according to Glandon and Miller, "was designed to push crabs to their limits to determine if a response to acidification existed." Data collected to gauge a response included crab growth per molt, the length of the inter-molt period, and rates of food consumption.

So what did their analysis reveal for such harsh and somewhat unrealistic future conditions?

With respect to the impact of ocean acidification, Glandon and Miller report that elevated pCO2 (alone or in combination with temperature) had no significant effect on crab growth or survival, no influence on the duration of the inter-molt period and no impact on the amount of food the crabs consumed. Likewise, temperature had no impact on survival or growth per molt. However, elevated temperature positively impacted the amount of food consumed (i.e., more was consumed) and it shortened the inter-molt period.

In light of their findings, Glandon and Miller conclude that "juvenile blue crab may be able to mitigate some of the potential negative effects of increased temperature and acidity." And as for why this is the case, the two scientists note that "the absence of a response to increased pCO2 of juvenile blue crab in this study may be related to the ability of estuarine species to tolerate a high level of environmental variability," given the high degree of variability of many environmental parameters that is often observed in estuarine environments, which variability has likely improved "the plasticity of response of blue crab to environmental stressors [so that they] have the capacity to thrive in a variety of conditions," such as elevated pCO2 and temperature as observed in their study. And that is good news for this important Chesapeake Bay species.

Posted 20 July 2017