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

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