- This research focused on population dynamics of two gelatinous zooplankters (Aequorea & Pyrosoma atlanticum) in the northern California Current to assess their relationship to environmental conditions and role in the pelagic ecosystem. Data collected since 1999 showed seasonal and interannual fluctuations in the abundance and distribution of Aequorea in the NCC, with a positive correlation with sea surface temperature and salinity. Pyrosoma atlanticum, which are typically found in tropical waters, have only been observed in high abundances in the NCC since 2014 and their role in the pelagic ecosystem is not well understood. Pyrosome abundance related to in situ environmental variables showed a positive correlation with warmer SST. We also used fatty acids as trophic markers to better understand pyrosome trophic ecology in the NCC. FA biomarkers suggest that pyrosomes have a broad phytoplankton diet, which may indicate an ability to inhabit warmer, lower nutrient zones.