Dw. Lea et al., CALCIUM-UPTAKE AND CALCIFICATION RATE IN THE PLANKTONIC FORAMINIFER ORBULINA-UNIVERSA, Journal of foraminiferal research, 25(1), 1995, pp. 14-23
We have developed a new stable isotope labeling technique to probe the
uptake of Ca2+ in foraminifera shells grown via live culturing. This
technique is based on the addition of the minor stable isotope 48Ca (n
atural abundance 0.19%) to seawater. The extent of Ca2+ uptake by fora
minifera can be assessed by determination of the 48/Ca-44 of the cultu
red shells using plasma mass spectrometry. This new technique could al
so be used to assess Ca2+ uptake in other CaCO3-secreting organisms. R
esults from labeling experiments indicate that almost all the Ca2+ in
the terminal spherical chamber of the planktonic foraminifer Orbulina
universa is in isotopic equilibrium with the surrounding seawater. Onl
y a very small fraction (<0.15 mug CaCO3 equivalent, or 0.5% of averag
e final shell mass) is likely to come from some other pool. If our res
ults apply generally to the precipitation of foraminifera shells, they
suggest that an internal cytoplasmic Ca2+ pool probably does not prov
ide a means by which seawater cation ratios can be fractionated. We ha
ve also applied the new labeling technique to the determination of inc
remental calcification rates in Orbulina universa. Our results indicat
e that adult calcification in individuals grown under high light is up
to three times greater than for individuals grown in the dark. This d
ifference is directly attributable to the role symbionts play in enhan
cing calcification. The enhancement in calcification rate is close to
the calculated increase in carbonate ion due to the photosynthetic act
ivity of the symbionts, suggesting that calcification rate in O. unive
rsa is proportional to the degree of carbonate saturation.