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The Response of the Grass Shrimp to Ocean Acidification and Warming

Paper Reviewed
Lowder, K.B., Allen, M.C., Day, J.M.D., Deheyn, D.D. and Taylor, J.R.A. 2017. Assessment of ocean acidification and warming on the growth, calcification, and biophotonics of a California grass shrimp. ICES Journal of Marine Science 74: 1150-1158.

The crustacean grass shrimp (Hippolyte californiensis) is able to change color from green to brown (and back again) via a process known as dynamic cryptic coloration (DCC). Common in a number marine species -- perhaps the most well-known of which are octopuses and cuttlefish -- this process of being able to rapidly change color allows these organisms to quickly react to changes in their environment, whereby they can quickly match the coloration of nearby structures, plants and/or animal species. DCC is important for providing both camouflage and visual communication; and in the words of Lowder et al. (2017), it "is achieved through physiological and morphological mechanisms that are sensitive to changes in environmental conditions." Consequently, there are concerns that projected future ocean acidification and warming may impact DCC in marine organisms. Lowder et al., therefore, set out to examine this possibility for the grass shrimp.

To accomplish their objective, the team of five University of California researchers subjected specimens of grass shrimp to three temperature and pH treatments in a controlled environment over a period of seven weeks, studying their growth, mineralization, transparency and spectral reflectance (coloration) responses under such conditions. The pH/temperature treatments included ambient (pH of 8.0 and temperature of 17°C), decreased pH (pH of 7.5 and temperature of 17°C) and decreased pH/increased temperature (pH of 7.5 and temperature of 19°C).

In discussing their findings, Lowder et al. say they found the grass shrimp H. californiensis to be "robust to both decreased pH and decreased pH/increased temperature in terms of growth (moult frequency, moult increment), exoskeleton mineralization (Ca and Mg content), and biophotonics (transmittance and spectral reflectance." Additionally, it was found that reduced seawater pH had no impact on mortality, carapace length or body mass. Thus, the authors of this study conclude that "these findings suggest that growth, calcification, and color of H. californiensis are unaffected by decreases of 0.5 pH units," which tolerance, they opine, "might stem from adaptation to the highly variable pH environment that these grass shrimp inhabit." Whatever the reason, the results of this study are welcomed news!

Posted 17 August 2017