Dataset: Carbon and nitrogen stable isotope measurements of gelatinous zooplankton and larval fish in the Northern California Current from March 2022 to August 2023

Gelatinous zooplankton and larval fish were collected using MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) tows in 25-meter (m) depth increments in the upper 100m of the water column (nets: 1 square meter (m²) with 333-micrometer (µm) mesh and 4 m² with 1000 µm mesh). Organisms in each tow were grouped by lowest visually identifiable taxon. Maximum and minimum lengths of individuals in each group were measured with a ruler and the volume of each sample of grouped individuals was measured by displacement. Samples were frozen at -20 degrees Celsius (°C) prior to preparation for stable isotope analysis.

Wet weight of each grouped sample was measured upon thawing the sample. Samples were dried at 60°C, then dry weights were measured. Samples were then crushed and homogenized using an agate mortar and pestle. Stable isotope compositions and carbon and nitrogen contents were measured by elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) at the UC Davis Stable Isotope Facility. Ash-free dry weights were determined by weighing samples before and after combusting dried samples at 500°C.