Dataset: Macroalgal carbon and nitrogen data collected as part of macroalgal surveys in Sitka Sound, Alaska kelp beds from 2018 to 2020

Coincident with monthly sampling of seawater for nutrient concentrations (see related dataset "Nutrient monitoring" https://www.bco-dmo.org/dataset/882057), we collected surface blades from M. pyrifera in the Breast Is. giant kelp bed from July 2018 - July 2019 to analyze for carbon (C) and nitrogen (N) content. On one frond from each plant (N = 3), we identified and removed the second intact blade closest to the frond’s scimitar blade. To capture seasonal variation in C and N content in kelp species in July 2018, January 2019, and August 2019, we collected blades from M. pyrifera plants (N = 5) at  ~1 m above their holdfasts and blades (N = 5) of N. fimbriatum and H. nigripes between 4 - 7 m depth (MLLW) at Samsing Pinnacle. We also opportunistically collected blades (N = 3-5) representing all kelp species present at Harris Is. in summer 2018 and 2020 and at Samsing Pinnacle in summer 2020. For all macroalgal tissue field collections, we immediately drained collected samples of excess seawater and kept them on ice in a covered cooler for transport to the lab. Within 2 hours of collection, we cleaned collected tissue of epiphytes and rinsed it briefly in fresh seawater. From all collected blades we excised 1 - 5 g of tissue immediately adjacent to the intercalary meristem where the blade meets the stipe. We spun tissue samples 10 times in a salad spinner before drying at 60 ℃ for at least 24 hrs. Dried samples were analyzed for C and N content (% dry mass) by the University of California Santa Cruz Stable Isotope Laboratory using a CE Instruments NC2500 elemental analyzer coupled to a Thermo Scientific DELTAplus XP isotope ratio mass spectrometer via a Thermo-Scientific Conflo III (routine measurement error ≤ 1.0 %C and ≤ 0.2 %N). 

Additional Funding Details:
In addition to primary funding from the NSF award OCE-1752600 additional funding was provided from The David and Lucile Packard Foundation and the North Pacific Research Board’s Graduate Student Research Award (1748-01) to Lauren Bell, PhD University of California Santa Cruz, Award title: "Fish Habitat, Fishes and Invertebrates, Lower Trophic Level Productivity Effect of substrate on herring roe response to global change."