[Coral-List] Are there really almost no studies that show a decline in gross calcification under low pH?

Dennis Hubbard dennis.hubbard at oberlin.edu
Tue Apr 5 09:44:28 EDT 2016


This is a bit outside of my focal area, but I have been following it with
great interest. I spent most of my limited time at the recent Ocean
Sciences meeting in the OA session and here is what I went away with,
admittedly with a heavy bias toward my own take on the excellent talks (I'd
have to spend time I don't have right now to couple my comments below to
specific presentations, so I refer you to the abstracts from that AGU
meeting in New Orleans).

- Clearly OA is a big deal - bad news
- Because corals can control the chemistry within their calcifying spaces
by ion pumping, what is going on in the ocean is for now decoupled from
open-ocean chemistry - good news.... and maybe local mitigation efforts CAN
have an impact
- But, this is an energy-intensive activity and, as other stresses
increase, there might be a level at which either other important functions
(e.g., reproduction, stress mitigation) will be compromised..... or the
total energy required for ion pumping will exceed what is available - bad
- One study that looked at corals under lab conditions associated with
atmospheric CO2 levels of 1000 ppm, showed no major decline in pH within
the calcifying space -very good news

So.... I think there is a good body of preliminary data out there that
suggests that simply documenting ocean chemistry MIGHT be an oversimplified
approach - one that could trigger funding but might not lead to useful
answers. The presentations I've seen and few the papers I've read suggest
that it's not as simple as "pH down.... corals gone". Also, simply counting
corals is probably not the solution either. As Chris Perry has shown,
bioerosion is an important counterpoint to all of this. However, to me, the
BIG missing piece of that equation is how increased storminess will affect
the sediment produced as well as the remaining reef structure. To my
knowledge, my research group at the old West Indies Lab remains as the only
group crazy enough and with enough time on our hands to systematically
measure sediment export under conditions ranging from fair weather to a CAT
5 hurricane.... and I doubt there is a real groundswell to do more of
these, however valuable they might be. But... folks like Curt Storlazzi are
doing some great things with field measurements and modeling to look at the
physical side of the equation(s). The bottom line is that I think we can
identify the approach with the biggest bang for its buck if we all get
together and agree on the meaning of terms we toss around; I think much of
the dissention is over semantics and we have a lot to gain by understanding
that coral growth, reef building, calcification, linear extension.... and a
host of others are NOT the same thing and that what we call it matters.

For those who are interested and will be attending ICRS, a number of us
have been discussing getting together as an ad hoc discussion group to
consider the question, "what should we be measuring?". Anyone who is
interested can contact me offline; once we get our session organized, I'm
going to start thinking about how to pitch this to the organizers.



On Mon, Apr 4, 2016 at 1:49 PM, Thomas Krueger <thomas.krueger at epfl.ch>

> 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.
> --
> *Thomas Krueger */Postdoctoral Researcher/
> Laboratory for Biological Geochemistry | École polytechnique fédérale de
> Lausanne (EPFL)
> *P*: (+41) 21 69 38039
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Dennis Hubbard
Chair, Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"

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