European Geosciences Union Vienna, Austria (15-20 April 2007)


S. Reynaud, F. Houlbrèque, P. Martinez, I. Billy, D. Allemand, C. Ferrier-Pagès

Experiments were performed in laboratory, under controlled conditions, in order to investigate the effect of light and feeding on the d15N composition of zooxanthellae and animal tissue of Stylophora pistillata, a zooxanthellate coral.

One group of corals was fed twice a week with freshly collected zooplankton and compared to a starved control group. Each group was also cultivated under three light levels (80, 200 and 300 µmol photons m-2 s-1).

d15N value of the zooplankton was measured (6.75 ‰) during the course of the experiment. Results obtained showed that d15N values of coral tissue were significantly heavier than those of zooxanthellae: 7.65 ± 0.09 ‰ vs. 6.46 ± 0.10 ‰, for all culture conditions.

The d15N of coral tissue measured in each light condition was not different within each group of fed (ANOVA, P=0.9) or starved colonies (ANOVA, P=0.6).

When pooling data obtained under the 3 light levels, the d15N of fed coral tissue (7.36 ± 0.11 ‰) was lighter than the d15N of starved coral tissue (7.88 ± 0.12 ‰). We also observed a significant effect of feeding on d15N of zooxanthellae (ANOVA, P<0.0001).

The mean value was 5.95 ± 0.12 ‰ for fed and 7.00 ± 0.11 ‰ for starved colonies. We confirmed that d15N can be used as a proxy in identifying trophic status of corals.