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The Tolerance of a Scleractinian Coral to Ocean Acidification and Warming

Paper Reviewed
Krueger, T., Horwitz, N., Bodin, J., Giovani, M.-E., Escrig, S., Meibom, A. and Fine, M. 2017. Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification. Royal Society Open Science 4: 170038, http://dx.doi.org/10.1098/rsos.170038.

Assessing the resilience of corals and their potential to adapt to the dreaded twin evils of global warming and ocean acidification has been of considerable interest to scientists for some time now and was the subject of a recent investigation by Krueger et al. (2017).

The specimen of choice for their analysis was the scleractinian coral Stylophora pistillata, which maintains several habitats across the Red Sea. Focusing on colonies growing in the northern portion of the Red Sea (specifically the Gulf of Aqaba), the seven scientists designed an experiment to examine its response to the combined effects of elevated temperature and lowered seawater pH. The experiment was conducted in outdoor aquariums at the Interuniversity Institute for Marine Sciences in Eilat, Israel, where corals were subjected to a full factorial design of two temperature treatments and two pH levels over a period of 47 days. More specifically, ambient pH was approximately 8.1 and reduced pH was maintained at approximately 7.8. Seawater temperatures were kept at ambient and 5°C above ambient, the latter of which treatment temperature reached values 2.2°C above the long-term maximum monthly mean in the final ten days of the study.

So, how did the corals respond to these presumably stressful treatment conditions?

They loved it!

Krueger et al. report that S. pistillata showed "no signs of bleaching despite spending 1.5 months at 1-2°C above their long-term summer maximum (amounting to 11 degree heating weeks) and a seawater pH of 7.8." Instead, they found that "their symbiotic dinoflagellates exhibited improved photochemistry, higher pigmentation and a doubling in net oxygen production, leading to a 51% increase in primary productivity" (emphasis added). What is more, they note that both light and dark calcification were unaffected by the different treatment conditions.

Based on the above findings, Krueger et al. conclude that "Stylophora pistillata from the Gulf of Aqaba is resistant to summer conditions to be expected for the second half of the century," adding that "the positive effect of elevated temperature on key physiological parameters suggests that these corals are currently living at suboptimal temperatures." And that is great news worth reporting!

Posted 20 April 2018