Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
www.elsevier.com/locate/palaeo
E¡ect of light on skeletal N13C and N18O, and interaction with
photosynthesis, respiration and calci¢cation in
two zooxanthellate scleractinian corals
S. Reynaud-Vaganay a; *, A. Juillet-Leclerc b , J. Jaubert a , J.-P. Gattuso c
b
a
Observatoire Ocëanologique Europëen, Centre Scienti¢que de Monaco, Avenue Saint-Martin, MC-98000 Monaco, Monaco
Laboratoire des Sciences du Climat et de l'Environnement, Laboratoire mixte CNRS-CEA, F-91180 Gif-sur-Yvette Cedex, France
c
Laboratoire d'Ocëanographie de Villefranche, UMR 7093, CNRS-UPMC, Box 28, F-06234 Villefranche-sur-mer Cedex, France
Received 18 April 2000; received in revised form 15 November 2000; accepted 31 July 2001
Abstract
The respective role of environmental and physiological controls on the isotopic composition of coral skeletons is a
matter of debate. It has been shown that N13 C can be affected by light, seawater N13 CDIC , nutrition, respiration,
spawning, pH and temperature. We investigated the effect of light on photosynthesis, respiration, calcification, and
stable isotope composition (N13 C and N18 O) of the skeleton in the zooxanthellate scleractinian corals Acropora sp. and
Stylophora pistillata. Colonies were grown on glass slides under controlled conditions in the laboratory at low and high
light (LL and HL: 132 and 258 Wmol photons m32 s31 ). The average net photosynthesis of Acropora sp. was
significantly higher under HL than under LL. The difference was not statistically significant for S. pistillata. The
respiration rate did not change significantly in both species under the two light conditions. The calcification rate of S.
pistillata under HL was 17-fold higher than under LL and 2.5-fold higher for Acropora sp. The average skeletal N13 C
and N18 O of Acropora sp. were significantly more negative under LL than under HL. For S. pistillata, skeletal N18 O was
significantly more negative in the LL than in the HL condition. The N13 C value of the skeleton deposited under LL was
also more negative than under HL, although the difference was not statistically significant. The skeletal N13 C was
significantly correlated with the rate of calcification, both in LL and HL. No correlation was found between skeletal
N13 C and the following other physiological parameters: net and gross photosynthesis (Pn and Pg ), respiration (R), and
the Pg /R ratio. The increase of skeletal N13 C with increasing light seems to support the model of Goreau (1977).
Zooxanthellae mostly fix 12 C under HL, leading to an increased concentration of 13 C in the common carbon pool which
supplies dissolved inorganic carbon (DIC) for calcification. Hence, the skeleton deposited is isotopically enriched in
13
C. This general model needs revision to accommodate the recent finding that calcification and photosynthesis draw
carbon from two reservoirs (seawater and metabolic DIC), and that respiratory CO2 is the major source of DIC for
calcification. It is suggested that zooxanthellae mostly fix 12 C[DIC] in LL; the organic matter respired, the CO2
released, and the CaCO3 deposited being therefore isotopically light. Under HL condition, zooxanthellar
photosynthesis uses both [12 C]- and [13 C]DIC. The photosynthetic products catabolized by the coral, as well the
respiratory CO2 and the CaCO3 precipitated are therefore heavier. ß 2001 Elsevier Science B.V. All rights reserved.
* Corresponding author. Fax: +377-92-16-79-81.
E-mail address: [email protected] (S. ReynaudVaganay).
Keywords: corals; isotopes; oxygen; carbon; culture; light
0031-0182 / 01 / $ ^ see front matter ß 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 0 3 1 - 0 1 8 2 ( 0 1 ) 0 0 3 8 2 - 0
PALAEO 175 27-12-01
394
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
1. Introduction
Causes of the variations in the N13 C of coral
skeletons have been a matter of debate (Weber
and Woodhead, 1970; Erez, 1978; Swart, 1983;
McConnaughey, 1989). Aragonite deposited by
scleractinian corals is usually depleted in 13 C relative to equilibrium with ambient seawater as a
result of kinetic and metabolic fractionation. Kinetic fractionation occurs during CO2 hydration
and hydroxylation (McConnaughey, 1989); metabolic fractionation produces additional changes in
skeletal N13 C re£ecting changes in photosynthesis
and respiration (Swart, 1983; McConnaughey,
1989; Muscatine et al., 1989; McConnaughey et
al., 1997).
The two external sources of carbon available to
corals are dissolved inorganic carbon (DIC) in the
surrounding seawater (which has a mean N13 C
close to 1x) and zooplankton (with N13 C values
more negative). The three physiological processes
that can potentially alter the carbon pool available to corals are photosynthesis, respiration and
feeding. It has been suggested that calci¢cation
takes place from an internal inorganic carbon
pool (Goreau, 1977; Erez, 1978) composed of carbon derived from seawater and from metabolic
activity, and modi¢ed by fractionation during
CO2 uptake by photosynthesis. Similar pools exist
in foraminifera (Kuile and Erez, 1987). It was
suggested that the light isotope (12 C) was preferentially used by zooxanthellae for photosynthesis
during periods of high photosynthesis, leading to
an increased concentration of 13 CO2 in the carbon
pool available for the calci¢cation. Then, skeletons precipitated during periods of high photosynthesis should be isotopically heavier (Swart,
1983; McConnaughey, 1989; McConnaughey et
al., 1997). It was suggested that the change of
photosynthesis rate during the course of the year
may be responsible for producing a cyclic change
in the skeletal N13 C (Swart et al., 1996). Increased
heterotrophy should have an opposite e¡ect leading to a decrease in skeletal N13 C levels since zooplankton has a low N13 C value relative to seawater.
Heterotrophy and photosynthesis are linked
and are di¤cult to separate in ¢eld experiments.
Coral cultures enable the investigation of each
parameter at a time. The study of Weil et al.
(1981) successfully used cultured corals to investigate the e¡ect of temperature and irradiance on
the skeletal N18 O and N13 C of the corals Montipora
verrucosa and Pocillopora damicornis. Here, we
investigate the e¡ect of light on photosynthesis,
respiration, calci¢cation, and stable isotope composition (N13 C and N18 O) of the skeleton in the
zooxanthellate scleractinian corals Acropora sp.
and Stylophora pistillata. Colonies were grown
on glass slides under controlled conditions in the
laboratory at low and high irradiance as previously described (Reynaud-Vaganay et al., 1999).
2. Materials and methods
2.1. Biological material
The experiment was conducted in the laboratory using colonies of the branching zooxanthellate
scleractinian corals, Stylophora pistillata (Esper,
1797) and Acropora sp. Tips from 24 branches
were sampled from a single parent colony of
Acropora sp., and 20 tips from a di¡erent colony
of S. pistillata. These tips were propagated from
parent colonies collected in the Gulf of Aqaba.
The specimens were glued on glass slides
(3U6U0.2 cm) using underwater epoxy (Devcon0) as described by Reynaud-Vaganay et al.
(1999), and randomly distributed in two aquaria
(15 l). The tanks were supplied with heated Mediterranean seawater (24³C) pumped from a depth
of 50 m. The seawater renewal rate was approximately ¢ve times per day and the seawater was
continuously mixed with a Rena0 pump (6 l
min31 ). Light (258 and 132 Wmol m32 s31 ) was
provided by metal halide lamps (Philips HPIT,
400 W) on a 12:12 photoperiod. Seawater was
continuously aerated with outside air. The culture
temperature (25³C) was controlled to within
þ 0.1³C using a temperature controller (EW, PC
902/T). All colonies were cultured for 54 days.
All colonies were initially cultured for 6 weeks
under a light intensity of 132 Wmol m32 s31 . The
ring skeleton deposited on the glass slide was then
removed with a scalpel (Reynaud-Vaganay et al.,
PALAEO 175 27-12-01
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
1999), dried overnight at room temperature and
stored in glass containers pending isotopic analyses. Thereafter, colonies were cultured for an additional period of 6 weeks under a light intensity
of 258 Wmol m32 s31 . Skeletal samples were collected as described above at the completion of
each period for determination of the isotopic
composition.
2.2. Isotopic measurement
Following the treatment described by Boiseau
and Juillet-Leclerc (1997), the skeletal material
was ground and the powder soaked in hydrogen
peroxide (30%, v/v) for 12 h to eliminate the organic matter, ¢ltered on Nucleopore polycarbonate membranes (0.4 Wm), and dried at 40³C for
4 h. A sub-sample of 100 Wg of aragonite powder
was dissolved in 95% H3 PO4 at 90³C (Craig,
1957). The CO2 gas evolved was analyzed using
a VG Optima mass spectrometer with a common
acid bath. The data are expressed in the conventional delta notation relative to a standard, which
is PDB for carbonates :
13 12
… C= C†sample
13
N C ˆ 13 12
31 U103
… C= C†standard
18 16
… O= O†sample
18
N O ˆ 18 16
31 U103
… O= O†standard
The external precision, estimated using an internal standard, is 0.11x (S.D.) for carbon, and
0.08x (S.D.) for oxygen. The reproducibility of
carbon and oxygen isotopic measurements calcu-
395
lated from replicate coral samples is respectively
0.10x and 0.08x (S.D.) for Acropora sp., and
it is 0.11x and 0.12x (S.D.) for Stylophora
pistillata.
The carbon and oxygen isotope composition of
seawater was measured on samples collected once
a week. Samples were poisoned with HgCl2 solution (1 ml of saturated HgCl2 in 60 ml of seawater) to prevent any further biological activity.
The reproducibility of carbon isotope measurements from seawater was þ 0.07x (S.D.). By
subtracting the N13 CDIC from the skeletal N13 C,
the true change in N13 C resulting solely from physiological and kinetic processes can be calculated.
The reproducibility of oxygen isotope measurements was þ 0.05x (S.D.). The skeletal N18 O was
corrected for changes in seawater N18 O (Hut,
1987).
2.3. Measurements of environmental parameters
Irradiance was measured using a 4 Z quantum
sensor (Li-Cor, LI-193SA) once a week (Table 1).
Temperature (precision : þ 0.05³C) was logged at
10 min intervals using a Seamon0 temperature
recorder. Dissolved oxygen concentration was
measured using a polarographic electrode (Ponselle) calibrated daily against air-saturated seawater and a saturated solution of sodium sul¢te
(zero oxygen). pH was measured using a combined Ross pH electrode (Orion 8102SC) calibrated daily against N.B.S. bu¡ers (pH 4.006
and pH 7.413 at 25³C). Determination of total
alkalinity was carried out potentiometrically according to the method described by Gran
Table 1
Light and chemical characteristics of the seawater used in the culture tanks (mean þ S.E.M.; the sample size is shown in parentheses)
32
31
Light (Wmol m s )
Temperature (³C)
Salinity
Seawater N18 O (x vs. SMOW)
Seawater N13 C (x vs. PDB)
pH (N.B.S.)
Total alkalinity (meq kg31 )
Dissolved O2 (Wmol kg31 )
Aquarium 1
Aquarium 2
132 þ 12 (n = 6)
25.1 þ 0.1 (n = 4996)
38.0 þ 0.1 (n = 16)
1.29 þ 0.02 (n = 10)
0.82 þ 0.09 (n = 10)
8.143 þ 0.001 (384)
2.676 þ 0.005 (5)
189.0 þ 0.3 (292)
258 þ 13 (n = 6)
25.1 þ 0.2 (n = 5982)
38.0 þ 0.1 (n = 11)
PDB: Pee Dee Belemnite, SMOW: Standard Mean Ocean Water, N.B.S.: National Bureau of Standards.
PALAEO 175 27-12-01
396
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
(1952). Salinity was measured with a conductivity
meter (Meter LF 196).
2.4. Photosynthesis and respiration
Photosynthesis and respiration were measured
using the oxygen technique.
The experimental sequence was identical for
each coral: nubbin was taken from the culture
aquarium, placed in a perspex chamber (240 ml)
containing ¢ltered seawater, for a 30 min pre-incubation in the light (132 or 258 Wmol photons
m32 s31 , depending on culture condition). The
colony was then incubated for 1 h in the same
chamber in order to measure the rate of photosynthesis. The chamber was then £ushed and the
coral pre-incubated for 30 min in the dark, and
after 1 h in the dark to measure the respiration
rate. The incubation medium was continuously
agitated using a magnetic stirrer, and changed
after each incubation. The respirometric chamber
was kept at 25³C in a thermostated water bath.
All incubations took place between 08:00 and
14:00. The colonies were subsequently returned
to the culture aquarium. Oxygen concentration
was monitored in the chamber and stored every
1 min using a data-logger (LI-1000, Li-Cor Inc.).
Dissolved O2 was measured using a Ponselle polarographic electrode calibrated as described
above. The rates of net photosynthesis and respiration were estimated using a linear regression of
O2 against time. Photosynthesis and respiration
values were then normalized with the surface of
the coral estimated using the aluminum foil technique (Marsh, 1970).
Gross photosynthesis was calculated using the
following formula :
Pg ˆ
calci¢cation rate was measured using the following formula :
r
n Pn
31
Gˆ
P0
Where G is the calci¢cation rate, n is the number of culture days, Pn is the dry weight after
n days of culture, P0 is the initial dry weight.
2.6. Statistical analysis
Statistical analysis was performed using JMP
3.1.6 (SAS Institute, Cary, USA). Results are expressed as mean þ S.E.M. n is the sample size.
3. Results
The environmental conditions used during the
culture experiment are shown in Table 1.
The rate of survival of Stylophora pistillata was
43% in the low light (LL) but reached 70% in the
high light (HL) condition. For Acropora sp., the
survival rate was higher in the LL than in the HL
conditions (80% vs. 67%).
3.1. Calci¢cation
The calci¢cation rates of Acropora sp. and Stylophora pistillata were statistically di¡erent (anal-
12UPn
24UR
Where Pg is the gross photosynthesis, Pn the net
photosynthesis, and R the respiration rate.
2.5. Calci¢cation
Corals were weighted using the buoyant weight
technique (Jokiel et al., 1978; Davies, 1989) at the
beginning and at the end of the experiment. The
Fig. 1. Daily calci¢cation rate for both species (Acropora sp.
and Stylophora pistillata) versus light (n = 19 and 7 for
Acropora sp., and n = 7 and 14 for S. pistillata, respectively
under LL and HL; mean þ S.E.M.).
PALAEO 175 27-12-01
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
397
ysis of variance (ANOVA), P 6 0.0001; Fig. 1).
There is also a signi¢cant e¡ect of light regime
in both species (ANOVA, P 6 0.0001). The calci¢cation rate of Acropora sp. under HL was 2.5fold higher than under LL (0.649 vs. 0.261%
day31 ), and 17-fold higher for S. pistillata (0.400
vs. 0.023% day31 ).
3.2. Photosynthesis and respiration
Net photosynthesis and respiration values were
normalized per units of coral area, and shown in
Fig. 2. The average net photosynthesis of Acropora sp. was signi¢cantly higher under HL than
under LL (0.7 vs. 0.3 Wmol O2 cm32 h31 ; ANOVA, P = 0.0002). The di¡erence was not statistically signi¢cant for Stylophora pistillata (ANOVA, P = 0.4), but the sample size was small
(n = 2 or 3).
The rate of respiration was signi¢cantly higher
in Acropora sp. than in Stylophora pistillata (ANOVA, P = 0.008). It was slightly higher under HL
than under LL in both Acropora sp. (0.39 vs. 0.31
Wmol O2 cm32 h31 ) and S. pistillata (0.16 vs. 0.14
Fig. 2. Net photosynthesis and respiration (Wmol O2 cm32
h31 ) as a function of light in Acropora sp. and Stylophora
pistillata (n = 19 and 16 for Acropora sp., and n = 3 and 2 for
S. pistillata, respectively under LL and HL; mean þ S.E.M.).
Fig. 3. Skeletal N13 C versus light in Acropora sp. and Stylophora pistillata (n = 18 for Acropora sp., and n = 3 and 2 for
S. pistillata, respectively under LL and HL; mean þ S.E.M.).
Wmol O2 cm32 h31 ). The e¡ect of the light conditions was not, however, statistically signi¢cant
(ANOVA, P = 0.2).
3.3. Skeletal N13 C
The seawater N13 CDIC remained relatively constant both during a diel cycle (0.95 þ 0.06x vs.
PDB, n = 4) and during several months
(0.82 þ 0.09x vs. PDB, n = 10). The average skeletal N13 C of Acropora sp. was lighter under LL
than under HL (33 vs. 32.7x; Fig. 3). This
di¡erence was statistically signi¢cant (ANOVA,
P = 0.04). The skeletal N13 C value of Stylophora
pistillata deposited under LL appeared also
more negative than under HL (33.5 vs.
32.9x), but the di¡erence was not statistically
Fig. 4. Skeletal N13 C versus calci¢cation rate in Acropora sp.
PALAEO 175 27-12-01
398
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
Fig. 5. Skeletal N13 C versus net and gross photosynthesis (Pn and Pg ), respiration (R), and the Pg /R ratio in Acropora sp.
(mean þ S.E.M.).
signi¢cant (ANOVA, P = 0.5). The range of variation of the skeletal N13 C was very similar for
both light regimes : 1.7x for Acropora sp. and
1.6x for S. pistillata. The skeletal N13 C of Acropora sp. was signi¢cantly correlated with the rate
of calci¢cation, in both light treatments (Fig. 4;
P = 0.05 and 0.01 for LL and HL, respectively).
No correlation was found, in Acropora sp., between the skeletal N13 C and the following other
physiological parameters (Fig. 5): net and gross
photosynthesis (Pn and Pg ), respiration (R), and
the Pg /R ratio.
3.4. Skeletal N18 O
Seawater N18 O (N18 Osw ) remained relatively constant during the experiment (1.29 þ 0.02x vs.
SMOW, n = 10).
The average skeletal N18 O values of Acropora
sp. and Stylophora pistillata were signi¢cantly
more negative under LL than under HL (respectively 34.2 vs. 33.8x and 33.8 vs. 33.1x;
Fig. 6). These di¡erences are statistically signi¢cant (ANOVA, P 6 0.0001 for Acropora sp. and
P = 0.04 for S. pistillata).
4. Discussion
4.1. Photosynthesis and respiration
Photosynthesis is light-enhanced, until saturating light intensities are reached (Jacques et al.,
1983; Falkowski et al., 1990). In the present
study, we have measured an increase of net photosynthesis when the light was doubled. This conclusion is in agreement with previous studies (Porter et al., 1984; McCloskey and Muscatine, 1984)
which observed that net and gross production
normalized per surface area declined in deep or
PALAEO 175 27-12-01
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
Fig. 6. Skeletal N18 O versus light in Acropora sp. and Stylophora pistillata (n = 18 for Acropora sp., and n = 3 and 2 for
S. pistillata, respectively under LL and HL; mean þ S.E.M.).
shade-adapted corals. Net photosynthesis values
measured in the present study (0.4 and 0.5 Wmol
O2 cm32 h31 ) are very close to those obtained by
Porter et al. (1984) for Stylophora pistillata (0.4
and 0.6 Wmol O2 cm32 h31 , respectively under LL
and HL conditions). Net photosynthesis values
measured for Acropora sp. (0.3 and 0.7 Wmol O2
cm32 h31 ) are within the range reported by Rogers and Salesky (1981) for Acropora palmata (0.4^
1.4 Wmol O2 cm32 h31 ).
We did not ¢nd a signi¢cant e¡ect of irradiance
on the respiration rate. This is in agreement with
data obtained in situ for Acropora formosa (Juillet-Leclerc et al., 1997b). But numerous other
studies have reported that the rate of respiration
decreases when light declines (e.g. Falkowski and
Dubinski, 1981; McCloskey and Muscatine,
1984; Gattuso, 1985). Such a decrease is probably
the result of reduced carbon production by the
symbiotic algae leading to a decreased availability
of organic carbon for the animal host.
4.2. Calci¢cation
It has long been thought that photosynthesis
stimulates calci¢cation. The basis of this hypothesis is the observation that calci¢cation is higher
in the light than in the dark: a recent review of
399
the literature showed that the median ratio of
light:dark calci¢cation is 3.0 (Gattuso et al.,
1999). In this study we have measured, for the
same light, a calci¢cation rate higher for Acropora
sp. than for Stylophora pistillata (11 times higher
under LL and twice under HL). The calci¢cation
rate of S. pistillata under HL was 17-fold higher
than under LL (0.400 vs. 0.023% day31 ), and 2.5fold higher for Acropora sp. (0.649 vs. 0.261%
day31 ). These results are in agreement with the
laboratory study of Houck et al. (1977) who observed a decrease of the growth rate of Porites
lobata and Pocillopora damicornis when the light
decreased. Oliver et al. (1983) have also shown a
calci¢cation rate higher for shallow corals. On the
other hand, it has been shown that calci¢cation
can be higher under LL (Gladfelter and Monahan, 1977), and that it can be inhibited under
HL (Goreau, 1959). Dodge et al. (1984) and Rinkevich and Loya (1984) did not observe any relationship between light and calci¢cation. Gattuso
(1985) has measured a maximum calci¢cation rate
for colonies of S. pistillata sampled at 10 m in the
Gulf of Aqaba. The calci¢cation rate decreases
between 10 and 30 m, in relation with light attenuation.
4.3. Stable isotopes
The respective role of environmental and physiological controls on the isotopic composition of
coral skeletons is a matter of debate (Swart,
1983). It has been shown that skeletal N13 C of
corals can be a¡ected by several parameters: light
(e.g. Fairbanks and Dodge, 1979; Juillet-Leclerc
et al., 1997a; Swart et al., 1996), seawater N13 CDIC
(Nozaki et al., 1978; Swart et al., 1996), nutrition
(Felis et al., 1998; Grottoli and Wellington, 1999),
respiration (Swart et al., 1996), and spawning
(Kramer et al., 1993; Gagan et al., 1994, 1996).
Recently, it has been suggested that foraminiferal
N13 C can also be a¡ected by the pH of the seawater (Spero et al., 1997) and temperature (Bemis
et al., 2000).
The possibility of diurnal variations in the 13 C/
12
C ratio of DIC in seawater has little been investigated, although information on the magnitude
of change in N13 CDIC would be important in the
PALAEO 175 27-12-01
400
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
interpretation of carbon isotope ratios in biogenic
carbonates. Weber and Woodhead (1971) observed that DIC was enriched in 13 C during daylight hours relative to the same water at night.
Weil et al. (1981) also observed a diurnal cycle
in N13 CDIC values of the seawater from reef, but
no consistent trends over weeks was observed.
These authors concluded that coral N13 C does
not simply re£ect ambient water mass conditions.
Swart et al. (1996) have measured a seasonal variation of the N13 CDIC which may re£ect the overall
productivity of the reef community, with periods
of maximum light availability being associated
with heaviest seasonal N13 C values. In the present
study it has been shown that seawater N13 CDIC
values remain relatively constant both during a
diel cycle as well as over several months, this is
likely due to a small biomass relative to the
aquarium volume, and to a high seawater renewal
rate.
Skeletal N13 C can be a¡ected by nutrition (Felis
et al., 1998; Grottoli and Wellington, 1999). Given that zooplankton and particulate organic matter have a low carbon isotopic composition (between 314 and 325x vs. PDB; Rau et al.,
1990), high levels of heterotrophic feeding in corals should be accompanied by a decrease in the
N13 C values of coral skeleton.
The relationship between light and skeletal N13 C
has been investigated by analyzing the e¡ects of:
depth (Land et al., 1975; Weber et al., 1976; Fairbanks and Dodge, 1979; McConnaughey, 1989;
Muscatine et al., 1989; Aharon, 1991; Leder et
al., 1991; Carriquiry et al., 1994; Juillet-Leclerc
et al., 1997a; Grottoli and Wellington, 1999),
cloud cover (Fairbanks and Dodge, 1979; Pa«tzold, 1984; Quinn et al., 1993; Boiseau et al.,
1998), and seasonality (Fairbanks and Dodge,
1979; McConnaughey, 1989; Cole and Fairbanks,
1990; Shen et al., 1992; Carriquiry et al., 1994;
Gagan et al., 1994; Wellington and Dunbar,
1995; Swart et al., 1996). The results are at times
contradictory and no conclusive understanding of
the e¡ect of light on skeletal N13 C has yet been
achieved. Skeletal N13 C has been shown to increase when light increases (e.g. between 33.79
and 32.04x for Acropora formosa; Juillet-Leclerc et al., 1997a; and between 34.65 and
+0.30x for Pavona clavus; Grottoli and Wellington, 1999). On the other hand, skeletal N13 C
has been observed to decrease when light increases (e.g. Swart et al. (1996) have shown that
skeletal N13 C ranged between 31.3 and 34.7x).
Swart et al. (1996) have also suggested that
skeletal N13 C increases with increasing respiration
rate. But this is unlikely because the incorporation
of light-respired CO2 would result in a decrease of
skeletal N13 C. It has also been suggested that
spawning a¡ects skeletal N13 C (Kramer et al.,
1993; Gagan et al., 1994, 1996), as the energy
used during the formation of gametes induces a
carbon isotopic depletion in coral skeletons
(Kramer et al., 1993). On the other hand, Gagan
et al. (1994) have assumed the gametes have a
carbon isotope composition similar to that of
the coral tissue (Land et al., 1975), gamete maturation may form a signi¢cant sink for 12 C resulting in 13 C enrichment of the skeleton. Finally,
Spero et al. (1997) proposed that an increase of
seawater carbonate concentration decreases the
N13 C of foraminiferal calcite shells.
A relationship between foraminiferal shells N13 C
and temperature has been observed in the study
of Bemis et al. (2000). The positive correlation
was observed for Orbulina universa (a symbiotic
species), and a negative correlation was observed
for Globigerina bulloides (a non-symbiotic species).
As skeletal N13 C could be a¡ected by several
environmental parameters, the study of specimens
cultured under controlled conditions is the only
way to investigate the e¡ect of one parameter
on the physiology and skeletal composition of
scleractinian corals (Reynaud-Vaganay et al.,
1999). In the present study, the corals were not
fed, pH and temperature were maintained constant, the seawater N13 CDIC was also constant,
no spawning event was observed, and the respiration rate did not change signi¢cantly in both species under the two light conditions. Therefore,
only light can have signi¢cantly controlled skeletal N13 C.
Values of skeletal N13 C measured in the present
study ranged between 32.7 and 33x for Acropora sp., and between 32.9 and 33.5x for Stylophora pistillata. Swart et al. (1996) have mea-
PALAEO 175 27-12-01
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
sured skeletal N13 C between 31.3 and 34.7x
(mean = 32.9 þ 0.3x) for Montastrea annularis
sampled in situ. Only Weil et al. (1981) have investigated the e¡ect of light on skeletal N13 C in
controlled conditions, they have measured a skeletal N13 C between 35.2 and 33.1x for Pocillopora damicornis, and between 33.2 and 30.4x
in Montipora verrucosa. Only M. verrucosa
showed a signi¢cant relationship between these
two parameters: skeletal N13 C increases when light
increases.
The increase of skeletal N13 C with increasing
light observed in this study seems to support the
model of Goreau (1977). There is an increased
¢xation of 12 C by zooxanthellae during periods
of elevated photosynthesis, leading to an increased concentration of 13 C in the carbon pool
which supplies DIC for calci¢cation. Hence, the
skeleton deposited is isotopically heavy. This general model needs a revision to accommodate the
recent ¢nding that calci¢cation and photosynthesis actually draw carbon from two reservoirs (seawater and metabolic DIC), and that respiratory
CO2 is the major source of DIC for calci¢cation
(Erez, 1978; Furla et al., 2000b). Since photosynthesis is a rapid process, the di¡usional pathway
of HCO3
3 does not provide enough carbon to
sustain photosynthesis (it only provides 15% of
zooxanthellar needs). Zooxanthellae must actively
pump bicarbonate, leading to an isotopic fractionation (Fig. 7). CO2 di¡usion into oral cells has
been shown to depend on ATPase activity (Furla
et al., 2000a). Once into the cells, CO2 is converted into HCO3
3 by a carbonic anhydrase in
order to avoid CO2 e¥ux. It is suggested that
zooxanthellae preferentially ¢x 12 C[DIC] in LL
(Fig. 7B); the organic matter produced is therefore isotopically light. Under HL condition
(Fig. 7A), zooxanthellar photosynthesis uses
both [12 C]- and [13 C]DIC, the photosynthetic
products catabolized by the coral are therefore
heavier.
CaCO3 precipitation uses two di¡erent sources
of carbon: coelenteric bicarbonate and metabolic
CO2 . The HCO3
3 di¡usional pathway is unaffected by light variations, but this pathway represents only 30% of the total carbon into the skeleton (Furla et al., 2000b). The mechanism used to
401
transport bicarbonate across the aboral epithelium is still unknown, but a transcellular pathway
has been suggested. Assuming that 70% of the
DIC used for calci¢cation is metabolic CO2 , the
skeleton deposited under HL is isotopically heavier. On the other hand, in LL (Fig. 7B), the organic matter respired, the CO2 released, and the
CaCO3 deposited are isotopically lighter.
The values of Acropora sp. skeletal N13 C were
signi¢cantly correlated with daily calci¢cation
rate, both in LL and HL. The skeletal N13 C became heavier when calci¢cation increased.
McConnaughey (1989) reached an opposite conclusion: rapid skeletal growth appears to be associated with depleted skeletal N13 C values. Erez
(1978) and Swart et al. (1996) did not observe
any correlation between skeletal N13 C and calci¢cation rate. No correlation was found between
skeletal N13 C and the following other physiological parameters: net and gross photosynthesis (Pn
and Pg ), respiration (R), and the Pg /R ratio. In a
previous study, Swart et al. (1996) have observed
an inverse relationship between N13 C of the coral
skeletons and P/R ratio. This inverse correlation
arises because of a slight positive association between N13 C and respiration rate. But the authors
observed no correlation between photosynthesis,
calci¢cation or extension and skeletal N13 C.
No signi¢cant light e¡ect on skeletal N13 C has
been observed in Stylophora pistillata, perhaps
due to the small number of samples (n = 2 or 3).
But the average skeletal N13 C was more negative
under LL. This trend agrees with the results obtained with Acropora sp.
The fate of oxygen during metabolic and photosynthetic processes is a subject which has received considerably less attention than that of carbon despite the fact that N18 O is widely used for
paleotemperature reconstruction.
The average skeletal N18 O values of Acropora
sp. and Stylophora pistillata measured in this
study were signi¢cantly more depleted under LL
than under HL conditions. This conclusion agrees
with those of Weber and Woodhead (1970) and
Erez (1978). Juillet-Leclerc et al. (1997b) have developed a mathematical model in order to de¢ne
the in£uence of calci¢cation processes on oxygen
isotopic composition. They concluded that rapid
PALAEO 175 27-12-01
402
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
Fig. 7. Proposal model of carbon isotopes incorporation into the coral skeleton light. CA = carbonic anhydrase; Z = zooxanthellae; M = mitochondria.
elongation should be associated with 18 O-enriched
skeleton. Grottoli and Wellington (1999) also observed a decrease of the skeletal N18 O under LL,
but the di¡erence was not signi¢cant. On the other hand, in a previous study in aquarium, Weil et
al. (1981) did not observe any variation of the
skeletal N18 O with the light. An opposite trend
was described by McConnaughey (1989) as kinetic isotopic behavior: rapid skeletal growth
often appears to be associated with strong kinetic
disequilibria, so the faster growing portions of
several photosynthetic corals are depleted in
18
O. The results obtained in the present study
raise the question of using oxygen isotopic composition of coral skeletons in paleoenvironmental
reconstruction.
Acknowledgements
Thanks are due to H. Spero for the N13 C
seawater analysis, to E. Tambuttë for advice with
the culture technique on glass slides, and to M.
Boiseau for her help with the mass spectrometer.
PALAEO 175 27-12-01
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
We are grateful to P. Furla for numerous
stimulating discussions, and to D. Allemand for
commenting on a draft of this manuscript.
References
Aharon, P., 1991. Recorders of reef environment histories:
stable isotopes in corals, giant clams, and calcareous algae.
Coral Reefs 10, 71^90.
Bemis, B.E., Spero, H.J., Lea, D.W., Bijma, J., 2000. Temperature in£uence on the carbon isotopic composition of Globigerina bulloides and Orbulina universa (planktonic foraminifera). Mar. Micropaleontol. 38, 213^228.
Boiseau, M., Juillet-Leclerc, A., 1997. H2 O2 treatment of recent coral aragonite: oxygen and carbon isotopic implications. Chem. Geol. 143, 171^180.
Boiseau, M., Juillet-Leclerc, A., Yiou, P., Salvat, B., Isdale, P.,
Guillaume, M., 1998. Atmospheric and oceanic evidences of
El Nin¬o-Southern Oscillation events in the south central
Paci¢c Ocean from coral stable isotopic records over the
last 137 years. Paleoceanography 13, 671^685.
Carriquiry, J.D., Risk, M.J., Schwarcz, H.P., 1994. Stable isotope geochemistry of corals from Costa Rica as proxy indicator of the El Nin¬o/Southern oscillation (ENSO). Geochim. Cosmochim. Acta 58, 335^351.
Cole, J.E., Fairbanks, R.G., 1990. The southern oscillation
recorded in the N18 O of corals from Tarawa atoll. Paleoceanography 5, 669^683.
Craig, H., 1957. Isotopic standards for carbon and oxygen and
correction factors for mass-spectrometric analysis of carbon
dioxide. Geochim. Cosmochim. Acta 12, 133^149.
Davies, P.S., 1989. Short-term growth measurements of corals
using an accurate buoyant weighing technique. Mar. Biol.
101, 389^395.
Dodge, R.E., Wyers, S.C., Frith, H.R., Knap, A.H., Smith,
S.R., Cook, C.B., Sleeter, T.D., 1984. Coral calci¢cation
rates by the buoyant weight technique: e¡ects of alizarine
staining. J. Exp. Mar. Biol. Ecol. 75, 217^232.
Erez, J., 1978. Vital e¡ect on stable-isotope composition seen
in foraminifera and coral skeletons. Nature 273, 199^202.
Fairbanks, R.G., Dodge, R.E., 1979. Annual periodicity of the
18 16
0/ 0 and 13 C/12 C ratios in the coral Montastrea annularis.
Geochim. Cosmochim. Acta 43, 1009^1020.
Falkowski, P.G., Dubinski, Z., 1981. Light-shade adaptation
of Stylophora pistillata, a hermatypic coral from the gulf of
Eilat. Nature 289, 172^174.
Falkowski, P.G., Jokiel, P.L., Kinzie, R.A. III., 1990. Irradiance and corals. In: Dubinsky, Z. (Eds.), Coral Reefs. Elsevier, pp. 89^107.
Felis, T., Pa«tzold, J., Loya, Y., Wefer, G., 1998. Vertical water
mass mixing and plankton blooms recorded in skeletal stable carbon isotopes of a Red Sea coral. J. Geophys. Res.
103, 30731^30739.
Furla, P., Orsenigo, M.N., Allemand, D., 2000a. Involvement
of H‡ -ATPase and carbonic anhydrase in inorganic carbon
403
absorption for endosymbiont photosynthesis. Am. J. Physiol. 278, R870^R881.
Furla, P., Galgani, I., Durand, I., Allemand, D., 2000b. Sources and mechanisms of inorganic carbon transport for coral
calci¢cation and photosynthesis. J. Exp. Biol. 203, 3445^
3457.
Gagan, M.K., Chivas, A.R., Isdale, P.J., 1994. High-resolution
isotopic records from corals using ocean temperature and
mass-spawning chronometers. Earth Planet. Sci. Lett. 121,
549^558.
Gagan, M.K., Chivas, A.R., Isdale, P.J., 1996. Timing coral
based climatic histories using 13 C enrichments driven by
synchronized spawning. Geology 24, 1009^1012.
Gattuso, J.-P., 1985. Features of depth e¡ects on Stylophora
pistillata, an hermatypic coral in the Gulf of Aqaba (Jordan,
Red Sea). Proceeding of 5th International coral reef congress, Tahiti, 6, pp. 95^100.
Gattuso, J.-P., Allemand, D., Frankignoulle, M., 1999. Photosynthesis and calci¢cation at cellular, organismal and community levels in coral reefs: A review on interactions and
control by carbonate chemistry. Am. Zool. 39, 160^183.
Gladfelter, E.H., Monahan, R.K., 1977. Primary production
and calcium carbonate deposition rates in Acropora palmata
from di¡erent positions in the reef. Proceeding of 3rd International Coral Reef Symposium 1, Miami, FL, pp. 389^394.
Goreau, T.F., 1959. The physiology of skeleton formation in
corals. I. A method for measuring the rate of calcium deposition by corals under di¡erent conditions. Biol. Bull. 116,
59^75.
Goreau, T.J., 1977. Coral skeletal chemistry: physiological and
environmental regulation of stable isotopes and trace metals
in Montastrea annularis. Proc. R. Soc. London B 196, 291^
315.
Gran, G., 1952. Determination of the equivalence point in
potentiometric titrations. Part II. Analyst 77, 661^671.
Grottoli, A.G., Wellington, G.M., 1999. E¡ect of light and
zooplankton on skeletal N13 C values in the eastern Paci¢c
corals Pavona clavus and Pavona gigantea. Coral Reefs 18,
29^41.
Houck, J.E., Buddemeier, R.W., Smith, S.V., Jokiel, P.L.,
1977. The response of coral growth rate and skeleton strontium content to light intensity and water temperature. Proceeding of 3rd International Coral Reef Symposium 2, Miami, FL, pp. 425^431.
Hut, G., 1987. Stable isotope reference samples for geochemical and hydrological investigations. Consultant group meeting IAEA. Vienna 16^18 September 1985. Report to the
Director General, IAEA, Vienna.
Jacques, T.G., Marshall, N., Pilson, M.E.Q., 1983. Experimental ecology of the temperate scleractinian coral Astrangia
danae. II. E¡ect of temperature, light intensity and symbiosis with zooxanthellae on metabolic rate and calci¢cation.
Mar. Biol. 76, 135^148.
Jokiel, P.L., Maragos, J.E., Franzisket, L., 1978. Coral
growth: buoyant weight technique. In: Stoddart, D.R., Johannes, R.E. (Eds.), Coral Reef: Research Methods.
Unesco, Paris. pp. 379^396.
PALAEO 175 27-12-01
404
S. Reynaud-Vaganay et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 175 (2001) 393^404
Juillet-Leclerc, A., Gattuso, J.-P., Montaggioni, L.F., Pichon,
M., 1997a. Seasonal variation of primary productivity and
skeletal N13 C and N18 O in the zooxanthellate scleractinian
coral Acropora formosa. Mar. Ecol. Prog. Ser. 157, 109^117.
Juillet-Leclerc, A., Montaggioni, L.F., Pichon, M., Gattuso, J.P., 1997b. E¡ects of calci¢cation patterns on the oxygen
isotope composition of the skeleton of the scleractinian coral
Acropora formosa. Oceanol. Acta 20, 645^658.
Kramer, P.A., Swart, P.K., Szmant, A.M., 1993. The in£uence
of di¡erent sexual reproductive patterns on density banding
and stable isotopic compositions of corals. Proceeding of 7th
International Coral Reef Symposium, Guam, 1, p. 222.
Kuile, B.T., Erez, J., 1987. Uptake of inorganic carbon and
internal carbon cycling in symbiont-bearing benthonic foraminifera. Mar. Biol. 94, 499^509.
Land, L.S., Lang, J.C., Barnes, D.J., 1975. Extension rate: a
primary control on the isotopic composition of West Indian
(Jama|«can) scleractinian reef coral skeletons. Mar. Biol. 33,
221^233.
Leder, J.J., Szmant, A.M., Swart, P.K., 1991. The e¡ect of
prolonged `bleaching' on skeletal banding and stable isotopic composition in Montastrea annularis. Coral Reefs 10,
9^27.
Marsh, J.A.J., 1970. Primary productivity of reef building calcareous red algae. Ecology 51, 255^263.
McCloskey, L.R., Muscatine, L., 1984. Production and respiration in the Red Sea coral Stylophora pistillata as a function of depth. Proc. R. Soc. London B 222, 215^230.
McConnaughey, T., 1989. 13 C and 18 O isotopic disequilibrium
in biological carbonates. I. Patterns. Geochim. Cosmochim.
Acta 53, 151^162.
McConnaughey, T.A., Burdett, J., Whelan, J.F., Paull, C.K.,
1997. Carbon isotopes in biological carbonates: respiration
and photosynthesis. Geochim. Cosmochim. Acta 61, 611^
622.
Muscatine, L., Porter, J.W., Kaplan, I.R., 1989. Resource partitioning by reef corals as determined from stable isotope
composition. I. N13 C of zooxanthellae and animal tissue vs
depth. Mar. Biol. 100, 185^193.
Nozaki, Y., Rye, D.M., Turekian, K.K., Dodge, R.E., 1978. A
200 year record of carbon-13 and carbon-14 variations in a
Bermuda coral. Geophys. Res. Lett. 5, 825^828.
Oliver, J.K., Chalker, B.E., Dunlap, W.C., 1983. Bathymetric
adaptations of reef-building corals, at Davies Reef, Great
Barrier Reef, Australia. I. Long-term growth of Acropora
formosa (Dana 1846). J. Exp. Mar. Biol. Ecol. 73, 11^35.
Pa«tzold, J., 1984. Growth rhythms recorded in stable isotopes
and density bands in the reef coral Porites lobata (Cebu,
Philippines). Coral Reefs 3, 87^90.
Porter, J.W., Muscatine, L., Dubinsky, Z., Falkowski, P.G.,
1984. Primary production and photoadaptation in light- and
shade-adapted colonies of the symbiotic coral, Stylophora
pistillata. Proc. R. Soc. London B 222, 161^180.
Quinn, T.M., Taylor, F.W., Crowley, T.J., 1993. A 173 year
stable isotope record from a tropical South Paci¢c coral.
Quat. Sci. Rev. 12, 407^418.
Rau, G.H., Teyssie, J.-L., Rassoulzadegan, F., Fowler, S.W.,
1990. 13 C/12 C and 15 N/14 N variations among size-fractionated marine particles: implications for their origin and trophic
relationships. Mar. Ecol. Prog. Ser. 59, 33^38.
Reynaud-Vaganay, S., Gattuso, J.-P., Cuif, J.-P., Jaubert, J.,
Juillet-Leclerc, A., 1999. A novel culture technique for scleractinian corals: application to investigate changes in skeletal
N18 O as a function of temperature. Mar. Ecol. Prog. Ser.
181, 121^132.
Rinkevich, B., Loya, Y., 1984. Does light enhance calci¢cation
in hermatypic corals? Mar. Biol. 80, 1^6.
Rogers, C.S., Salesky, N.H., 1981. Productivity of Acropora
palmata (Lamarck), macroscopic algae, and algal turf from
tague bay reef, St. Croix, US Virgin Islands. J. Exp. Mar.
Biol. Ecol. 49, 179^187.
Shen, G.L., Cole, J.E., Lea, D.W., Linn, L.J., McConnaughey,
T.A., Fairbanks, R.G., 1992. Surface ocean variability of
Galapagos from 1936^1982: calibration of geochemical tracers in corals. Paleoceanography 7, 563^588.
Spero, H.J., Bijma, J., Lea, D.W., Bemis, B.E., 1997. E¡ect of
seawater carbonate concentration on foraminiferal carbon
and oxygen isotopes. Nature 390, 497^500.
Swart, P.K., 1983. Carbon and oxygen isotope fractionation in
Scleractinian corals: a review. Earth-Sci. Rev. 19, 51^80.
Swart, P.K., Leder, J.J., Szmant, A.M., Dodge, R.E., 1996.
The origin of variations in the isotopic record of scleractinian corals: II. Carbon. Geochim. Cosmochim. Acta 60,
2871^2885.
Weber, J.N., Woodhead, P.M.J., 1970. Carbon and oxygen
isotope fractionation in the skeletal carbonate of reef-building corals. Chem. Geol. 6, 93^117.
Weber, J.N., Woodhead, P.M.J., 1971. Diurnal variations in
the isotopic composition of dissolved inorganic carbon in
seawater from coral reef environments. Geochim. Cosmochim. Acta 35, 891^902.
Weber, J.N., Deines, P., Weber, P.H., Baker, P.A., 1976.
Depth related changes in the 13 C/12 C ratio of skeletal carbonate deposited by the Caribbean reef-frame building coral
Montastrea annularis: further implications of a model for
stable isotope fractionation by scleractinian corals. Geochim. Cosmochim. Acta 40, 31^39.
Weil, S.M., Buddemeier, R.W., Smith, S.V., Kroopnick, P.M.,
1981. The stable isotopic composition of coral skeletons:
control by environmental variables. Geochim. Cosmochim.
Acta 45, 1147^1153.
Wellington, G.M., Dunbar, R.B., 1995. Stable isotopic signature of El Nin¬o Southern Oscillation events in eastern tropical Paci¢c reef corals. Coral Reefs 14, 5^25.
PALAEO 175 27-12-01