Nitrogen-15 Signals of Anthropogenic Nutrient Loading in Reef Corals

The 15N content of tissue from the coral Porites lobata was enriched, relative to corals from reference sites, at 5 of 7 Indo-Pacific sewage-affected reefs. Enrichment was as high as 3.7‰. The δ13C of sewage-affected corals suggests they maintained a high degree of autotrophic nutrition. 15N-enriched wastewater dissolved inorganic nitrogen (DIN), derived from untreated sewage, is the most likely cause for enrichment in coral tissue 15N, though changes in coral nutrition, metabolism and zooxanthellae population dynamics are possible additional factors. Isotopic measurements of coral tissue can provide a simple means of detecting wastewater uptake by corals.