Use of sucralose and caffeine as tracers of human waste in a coral reef ecosystem

Over the past ten years, divers have noted a decrease in healthy coral cover and an increase in benthic algae in Vatia Bay, on the island of Tutuila, American Samoa. The cause for this is unknown, but one hypothesis is that nutrient pollution from the local village may be driving the coral decline. Excess nutrients (especially nitrogen and phosphorus) can impact corals directly by lowering fertilization success, and reducing both photosynthesis and calcification rates, or indirectly such as through stimulation of the growth of benthic algae. Declining coral health adversely affects the biodiversity of the Bay and likely decreases ecosystem services. The objectives of this study were to determine the nutrient status of Vatia Bay (i.e. are levels elevated) and attempt to use caffeine and sucralose as tracers to assess the potential importance of human waste to the nutrient budget of the system. Water samples were collected monthly at sixteen sites, selected using a stratified random design, for analysis of nitrate, nitrite, ammonium, urea, total nitrogen, orthophosphorus, total phosphorus, silica and salinity. These data confirm that nutrient concentrations are elevated in the Bay, when compared to territorial water quality standards (total nitrogen