[Coral-List] [Cnidarian-dinoflagellate-symbiosis] Are there really almost no studies that show a decline in gross calcification under low pH?
matz at utexas.edu
Mon Apr 4 16:42:23 EDT 2016
Hi Thomas - one possible reason for the dearth of studies demonstrating coral sensitivity to acidification is that they are actually quite tolerant to it. See here:
On Apr 4, 2016, at 12:49 PM, Thomas Krueger <thomas.krueger at epfl.ch> wrote:
> Given the vast number of studies that show a decline in net calcification in individual corals as well as reef communities within the scope of a projected 2100 average ocean pH of around 7.8, I was wondering why there are only so few studies that have investigated the effect of low pH on the biologically determined gross calcification performance (i.e., before any deductions for skeleton dissolution have been made). In fact, we found only four (not counting Gagnon et al 2013). While Houlbreque et al. 2012 (Coral Reefs 31(1) 101-109) found initially no effect of pH 7.8 and 7.5 on gross calcification in Stylophora, it was half the control value for the same coral in a later study (Houlbreque et al 2015; L&O 60(1) 89-99). See also Tambutte et al 2015 (Nature communications DOI: 10.1038/ncomms8368) for no effect of pH 7.8 on porosity or linear extension in Stylophora pistillata (all three studies used Red Sea specimen). The work of Rodolfo-Metalpa et al. 2011 (Nature Climate Change DOI: 10.1038/NCLIMATE1200) demonstrated that two Mediterranean corals along a CO2 gradient show either no significant change or an actual increase in gross calcification for a pH of 7.7. Similarly, a later study by Rodolfo-Metalpa et al. 2015 (Global Change Biology 21, 2238–2248) shows no effect of pH 7.7 on the gross calcification in three cold water corals. What studies are we missing? Has nobody really observed changes in coral gross calcification in response to a "realistic" lower than ambient pH, which would indicate that the observed changes in net calcification for many of these corals are largely dissolution effects of existing skeleton. I am grateful for any helpful comments on this matter.
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