[Coral-List] Calcification measurements via the 45Ca-uptake vs total alkalinity anomaly technique

[Thomas Krueger]

Hi everyone,

thanks for all the responses and comments from coral-listers to a range 
of questions regarding coral calcification over the last year. 
Considering the large feedback and interest, we would like to share the 
final publication on the compatibility of 45Ca and TA calcification 
estimates with everyone.

https://peerj.com/articles/3749/

Cohen et al. 2017 "Measuring coral calcification under ocean 
acidification: methodological considerations for the 45Ca-uptake and 
total alkalinity anomaly technique"

As the oceans become less alkaline due to rising CO2 levels, deleterious 
consequences are expected for calcifying corals. Predicting how coral 
calcification will be affected by on-going ocean acidification (OA) 
requires an accurate assessment of CaCO3 deposition and an understanding 
of the relative importance that decreasing calcification and/or 
increasing dissolution play for the overall calcification budget of 
individual corals. Here, we assessed the compatibility of the 
45Ca-uptake and total alkalinity (TA) anomaly techniques as measures of 
gross and net calcification (GC, NC), respectively, to determine coral 
calcification at pHT 8.1 and 7.5. Considering the differing buffering 
capacity of seawater at both pH values, we were also interested in how 
strongly coral calcification alters the seawater carbonate chemistry 
under prolonged incubation in sealed chambers, potentially interfering 
with physiological functioning. Our data indicate that NC estimates by 
TA are erroneously ~5% and ~21% higher than GC estimates from 45Ca, for 
ambient and reduced pH, respectively. Considering also previous data, we 
show that the consistent discrepancy between both techniques across 
studies is not constant, but largely depends on the absolute value of 
CaCO3 deposition. Deriving rates of coral dissolution from the 
difference between NC and GC was not possible and we advocate a more 
direct approach for the future by simultaneously measuring skeletal 
calcium influx and efflux. Substantial changes in carbonate system 
parameters for incubation times beyond two hours in our experiment 
demonstrate the necessity to test and optimize experimental incubation 
setups when measuring coral calcification in closed systems, especially 
under OA conditions.

*--*

*Thomas Krueger */Postdoctoral Researcher/

Laboratory for Biological Geochemistry | École polytechnique fédérale de 
Lausanne (EPFL)

*P*: (+41) 21 69 38039