The sensitivity of corals, coccolithophorids and foraminifera to carbonate ion concentration a synth

1
The sensitivity of corals, coccolithophorids and
foraminifera to carbonate ion concentration a
synthesis Chris Langdon Rosenstiel School of
Marine and Atmospheric Science University of
Miami 4600 Rickenbacker Causeway Miami, FL
33149 Tel [phone] Fax [phone] clangdon
_at_rsmas.miami.edu Abstract For the purposes of
comparing the sensitivity of corals,
coccolithophorids and foraminifera to a change in
carbonate ion concentration or saturation state
it is convenient to normalize the calcification
rates to the rate at some defined concentration
or saturation state. This has the benefit of
removing the variability in absolute rates
between different organisms and allows one to see
the underlying similarity or dissimilarity in the
response. The sensitivity of twelve species of
coral to a change in CO32- or Ca2 has been
examined. The data reveal some diversity in the
response. One early study reported that
calcification increased with increasing Wa up to
a value of 3.0 and then remained constant up to a
value of 6.0. The bulk of the subsequent studies
suggest a linear relationship that goes to zero
at Wa1.0 and has a slope of 22-28 per unit
change in Wa (Fig. 1). The massive coral Porites
lutea, widely used in paleo-climatological
studies, is among this group of species
exhibiting a strong, linear dependence on
saturation state. There is a group of three
species that exhibit a much weaker dependence of
6-9 per unit change in Wa. A linear regression
through the data from all available studies gives
G -0.4522.7(Wa), r20.67, where G is the
calcification rate as a percentage of the
pre-industrial rate. The first-order rate law
G27.8(Wa-1) gives an equally good fit to the
data. If rates are regressed against CO32- the
relationship has a slope of 36 per 100 mmol
kg-1. Coccolithophorids in general exhibit a
much weaker dependence on CO32-. The exception
to this rule is the field population in the North
Pacific studied by Riebesell et al. 2000 which
had a sensitivity similar to that of coral (Fig.
2). Forams also exhibit a weaker dependence on
CO32- than corals over most of the range in
CO32- but with only two species studied it is
difficult to generalize (Fig. 3). There is a
clear need for more work on pelagic calcifiers
and a general need to better understand how other
environmental variables, in particular
temperature, interact with CO32- to control
calcification.
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Fig. 2 Comparison of the calcification rate of
coccolithophorids and corals to a change in
carbonate ion concentration.
Fig. 3 Comparison of the calcification rate of
foraminifera and corals to a change in carbonate
ion concentration.
Fig. 1 Compilation of studies on the effect of
aragonite saturation state on coral calcification.