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Marine Ecology Progress Series

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MEPS 392:103-110 (2009)  -  DOI:

Effect of light and feeding on the nitrogen isotopic composition of a zooxanthellate coral: role of nitrogen recycling

S. Reynaud1,*, P. Martinez2, F. Houlbrèque1,3, I. Billy2, D. Allemand1, C. Ferrier-Pagès1

1Centre Scientifique de Monaco, Avenue Saint Martin, 98000 Monaco, Principality of Monaco
2Département de Géologie et Océanographie, UMR CNRS 5805–EPOC, Université Bordeaux I, Avenue des facultés, 33405 Talence cedex, France
3Geological & Environmental Sciences Department, Stanford University, 450 Serra Mall, Bldg 320, Room 118, Stanford, California 94305-2115, USA

ABSTRACT: Experiments were performed in controlled conditions in order to investigate the effect of light and/or feeding on the δ15N composition of zooxanthellae and animal tissue of a scleractinian coral, Stylophora pistillata. For this purpose, corals were cultured under 3 light levels (80, 200, and 300 µmol photons m–2 s–1) and for each light level, half of the corals were fed twice a week with natural zooplankton while the other half, the control group, were starved. To understand how plankton ingestion changes the isotopic signal of the corals, zooplankton δ15N was also measured during the course of the experiment. It had a mean value of 6.75‰. No significant and consistent effect of light was observed on the δ15N of the tissue or zooxanthellae of S. pistillata. However, there was a significant depletion in tissue and zooxanthellae 15N of fed corals compared to the controls. This depletion did not follow the general food-web rule in which predators are enriched in 15N by 3.5‰ compared to prey, but can be explained by the fact that nitrogen is recycled within the symbiotic association. Indeed, in heterotrophic organisms, the enrichment is due to light nitrogen (14N) being preferentially excreted in the form of waste products into the environment, which leads to an increase in the δ15N signature of the animal. In corals, light waste products are instead recycled by the zooxanthellae, therefore depleting the isotopic signature of the zooxanthellae, and also of the host, by transfer of photosynthates with light nitrogen. These observations support the nitrogen-recycling rather than the nitrogen-conservation theory.

KEY WORDS: Stylophora pistillata · Corals · Nitrogen isotopic composition · Zooxanthellae · Tissues · Feeding · Culture

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Cite this article as: Reynaud S, Martinez P, Houlbrèque F, Billy I, Allemand D, Ferrier-Pagès C (2009) Effect of light and feeding on the nitrogen isotopic composition of a zooxanthellate coral: role of nitrogen recycling. Mar Ecol Prog Ser 392:103-110.

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