The southern California Current System (CCS) is a moderate upwelling system comprised of water masses with differing nutrient loadings and consequently community structure. The mesozooplankton community of the CCS is dominated by copepods and euphausiids; the copepod species Calanus pacificus is one of the two dominant copepod species in this region, and the dominant euphausiid species is Euphausia pacifica. The abundances of both of these species vary significantly with El Niño Southern Oscillation conditions. In order to investigate the hypothesis that these fluctuations are at least partially driven by changes in the food supply, we used the amino acid stable nitrogen isotope ratios of these organisms to examine potential changes in the source of nitrogen for primary production and zooplankton trophic position in years before and after the 1998-1999 ENSO event. Juvenile E. pacifica and CV and adult C. pacificus were sorted from zooplankton samples collected as part of routine CalCOFI quarterly sampling. Preliminary results show similar variability within both source and trophic aa; phenylalanine values varied between 2 and 8 per mil, while glutamic acid varied between 12 and 18 per mil. Results show variable trophic relationships around the ENSO event, though data is inconclusive regarding a clear coherent ENSO signal in the trophic indices of both species. Relationships can be obscured by variable hydrography in the dynamic region surrounding Pt. Conception, as well as differing water mass advection in years during and after ENSO events. In spite of this, different relationships with distance from shore can also be inferred, consistent with greater phytoplankton concentrations nearshore.