MEPS 280:105-114 (2004)  -  doi:10.3354/meps280105

Nutrient-induced perturbations to δ13C and δ15N in symbiotic dinoflagellates and their coral hosts

Ove Hoegh-Guldberg1,*, Leonard Muscatine2, Claire Goiran2, Dorthe Siggaard1, Guy Marion1

1Centre for Marine Studies, University of Queensland, St Lucia, Queensland 4067, Australia
2Department of Biology, University of California at Los Angeles, Los Angeles, California 90095, USA

ABSTRACT: Inorganic nutrients play a critical role in determining benthic community structure in tropical seas. This study examined the impact of adding inorganic nutrients (ammonium and phosphate) on the isotopic composition of 2 reef-building corals, Pocillopora damicornis and Heliofungia actiniformis, on the southern Great Barrier Reef. The addition of elevated nutrients to patch reefs that pond at low tide did not perturb the C:N ratio of either species or their symbiotic dinoflagellates. The C:N ratios were significantly higher in material extracted from the skeleton (14.8 ± 1.50 and 10.8 ± 1.42) than either host (7.6 ± 0.87 and 6.0 ± 0.71) or symbiotic dinoflagellates (5.7 ± 0.48 and 6.9 ± 0.66) (P. damicornis and H. actiniformis respectively; ±95 confidence intervals). The ratio of acquired N to background N suggests that the added dissolved inorganic nitrogen (DIN) accounted for 50 to 100% of total nitrogen within the tissues of P. damicornis and H. actiniformis at the end of the experiment. The addition of the isotopically depleted nutrients (δ15N = 0‰) to patch reefs significantly decreased δ15N from control values of between 3 and 4 to values to below 1 in the case of all compartments, while δ13C values were relatively unresponsive to nutrient treatments. These findings suggest that coral δ15N has the potential to provide a historical record of the δ15N of dissolved nitrogen surrounding reef-building corals and their symbiotic dinoflagellates.

KEY WORDS: Nutrients · Corals · δ15N · Eutrophication · Fertilizer use · ENCORE · Pocillopora · Heliofungia · Experimental geochemistry

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