CTD casts were performed at Friday Harbor, WA in August of 2021. These data were collected as part of the following study: Data collected as part of this study include nitrogen isotope ratio data for coral tissue and skeleton of the scleractinian cold-water coral Balanophyllia elegans collected at Friday Harbor, WA. Data was collected between March 2019 and August 2021. These data include paired measurements of the N isotope ratio (d15N) of coral tissue and skeleton. Tissue was measured using and Elemental Analyzer (EA)-coupled Isotope Ratio Mass Spectrometer (IRMS) and skeleton samples were first dissolved and organic nitrogen was oxidized to nitrate with persulfate before being run on a GC-IRMS with the denitrifier method. These data also include the results of two culture experiments with the same species of corals. The corals in the first culture experiment were fed Artemia diets with different known d15N in order to quantify change in the tissue d15N in response to a change in the food source and to determine the offset in d15N between the coral tissue and its diet. The starvation trial culture experiment was conducted to evaluate the effects of starvation on the d15N of coral tissue. For both experiments coral tissue was analyzed using an EA-IRMS. This data also includes the d15N of the respective Artemia diets. Finally, included in this data is hydrological and particulate matter data collect at the site the corals were collected (near Friday Harbor, WA). This data includes nitrate d15N and d18O, suspended particulate organic matter d15N, net tow material d15N, and data collected from a CTD profiler. This data enhances the understanding of cold-water coral diet and trophic position. This data improves the understanding of the relationship between surface nitrate d15N and the d15N recorded in the coral skeleton which is useful for enhancing the resolution of coral d15N paleoproxies.