Gut content and fatty acid analyses reveal trophic role of the ctenophore <i>Pleurobrachia bachei</i> in the Northern California current

ABSTRACT Within the highly productive Northern California Current (NCC) ecosystem, the ctenophore Pleurobrachia bachei is common, yet its trophic role remains unclear. Samples of P. bachei were collected from the NCC in 2018–2019 at two latitudes, including the Newport Hydrographic Line and Trinidad, during two seasons (summer and winter). Samples were dissected for gut contents and analyzed for fatty acid concentrations. The three most abundant prey categories found within P. bachei guts were consistently adult copepods, copepod eggs, and invertebrate eggs, although the relative contribution of these and other prey varied significantly between seasons and latitudes. Essential fatty acids, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) together made up nearly half of P. bachei fatty acid content. While this sum was consistent through space and time, EPA and DHA individually varied. Patterns in both P. bachei predation and fatty acid content track seasonal and latitudinal variability in this highly dynamic eastern boundary upwelling system, with seasons driving slightly larger differences. Our analyses suggest that P. bachei in the NCC acts as both an influential predator and an important prey source, highlighting the need to include P. bachei and other underappreciated gelatinous zooplankton in modeling of pelagic food webs.