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Warming Trumps Ocean Acidification in a Calcifying Green Algae

Paper Reviewed
Campbell, J.E., Fisch, J., Langdon, C. and Paul, V.J. 2016. Increased temperature mitigates the effects of ocean acidification in calcified green algae (Halimeda spp.). Coral Reefs 35: 357-368.

As described by Campbell et al. (2016) in their intriguing study, "the singular and interactive effects of ocean acidification and temperature on the physiology of calcified green algae (Halimeda incrassata, H. opuntia and H. simulans) were investigated in a fully factorial, 4-week mesocosm experiment," where "individual aquaria replicated treatment combinations of two pH levels (7.6 and 8.0) and two temperatures (28 and 31°C)," and where algal "rates of photosynthesis, respiration and calcification were measured for all species both prior to and after treatment exposure." And what did this study reveal?

As illustrated in the figure below, the four researchers report that (1) "after treatment exposure, net photosynthesis was unaltered by pH, yet significantly increased with elevated temperature by 58, 38 and 37% for H. increassata, H. simulans and H. opuntia, respectively," that (2) "both pH and temperature influenced calcification, but in opposing directions," that (3) "on average, calcification declined by 41% in response to pH reduction, but increased by 49% in response to elevated temperature," and that (4) "within each pH treatment, elevated temperature increased calcification by 23% (at pH 8.0) and 74% (at pH 7.6)."

And so it was that Campbell et al. confidently concluded that their study contributes to "an increasing number of reports" that suggest that moderate increases in temperature may serve to improve metabolic performance and mitigate the detrimental effects of ocean acidification.

Left Panel: Net photosynthesis in Halimeda opuntia, Halimeda simulans, Halimeda incrassata after 28 days of exposure to four treatments. Right Panel: Calcification rates of Halimeda opuntia and Halimeda simulans. Values from replicate specimens within a single tank were averaged to derive a tank mean. The statistical table in each panel displays ANOVA results (fixed factors: species, temperature, pH). Adapted from Campbell et al. (2016).

Posted 28 June 2016