Award: OCE-1537338

Coral reef ecosystems provide food and income for 1/5th of the global human population. In the United States and its territories, coral reefs cover more than 4 million acres in the Atlantic Ocean, Gulf of Mexico, Caribbean Sea, and the Pacific Ocean, where they support commercial and subsistence fisheries as well as jobs and businesses through tourism and recreation. For example, coral reefs in southeast Florida provide more than 70,000 jobs and generate $4.4 billion in sales each year. Yet, while coral reefs provide valuable services to human communities, they are also sensitive to human activities, both local and distant, that affect the conditions of the ocean in which coral reefs exist. This project supported the development and application of a new tool - nitrogen isotopes in the organic component of coral skeletons - to gain a better understanding of the relationship between ocean nitrogen concentrations and coral reef health. Nitrogen (N) is supplied to coral reefs from land-based sources, atmospheric deposition and from the surrounding oceans. In some areas including parts of Hawaii and Bermuda, land-based sources are contaminated by sewage and fertilizer, and in the northern South China Sea, N is carried in aerosol pollution from the adjacent continent. In three separate studies, traced these different sources of anthropogenic N into the corals and evaluated the consequences for the coral communities. In west Maui, nearshore corals are exposed to contaminated groundwater containing 50 times more N than normal seawater. We found the corals grew more slowly, and were heavily eroded. Conversely, on Bermuda, nearshore corals adjacent to groundwater discharge vents did not exhibit elevated bioerosion rates and we were not able to attribute changing coral growth rates directly to the excess N. We tested hypotheses that anthropogenically-sourced atmospheric N is impacting the surface oceans. Our 45-year long record of coral skeletal-bound nitrogen isotopes from Dongsha Atoll revealed increased deposition of anthropogenic atmospheric N on the west Pacific ocean and its incorporation into plankton and, in turn, the atoll corals. Conversely, our 130-year long Bermuda record does not show a long-term decline in the Anthropocene of the amplitude predicted by model simulations or observed in the Pacific coral. Rather, the decadal variations in the Bermuda record appear to be driven by the North Atlantic Oscillation (NAO), most likely, through changes in the formation of Subtropical Mode Water. A correlation between the nitrogen isotope time-series and coral growth rates on Bermuda suggests that nutrient supply to the reef is linked to the phase of the NAO, which exerts strong influence on coral growth in the region. In parallel with these analyses of "wild" corals, we conducted a laboratory-based coral culture experiment at the Bermuda Institute for Ocean Sciences designed to increase our understanding of the factors influencing nitrogen isotope incorporation into coral skeletons. We overcame a major obstacle to this type of investigation by constructing a biofilter that effectively removed all nitrogen from the intake water to the culture aquaria. This meant we were able to control all sources of nitrogen to the corals in culture. Our experiment revealed significant effects of light and feeding on the nitrogen isotope composition of corals and symbionts that reflect shifts in the importance of symbiont-sourced nitrogen to the coral host. Analyses of experimental products are still underway. The project supported the labs of three PI?s, two post-doctoral research projects, two PhD theses, one undergraduate senior thesis, and three undergraduate interns. To date, six scientific papers are published, under review or prepared for publication. Results of this work have also been shared at ten international conferences, workshops and seminars. Last Modified: 05/14/2018 Submitted by: Anne Cohen