UC San Diego

This study analyzes interannual variability in springtime carbon biomass of pelagic tunicates (salps, doliolids, pyrosomes, and appendicularians) over the period 1951-2002 from CalCOFI zooplankton samples taken in the southern sector of the California Current System. The results provide evidence for ecosystem changes between 1976 and 1977 and perhaps between 1998 and 1999. A cool-phase group of salps (Salpa maxima, Pegea socia, Cyclosalpa bakeri, and Cyclosalpa affinis) that was present between 1951 and 1976 was nearly undetectable in Southern California waters during the warm phase of the California Current (1977-98). C. bakeri and C. affinis then re-appeared in 2001. A persistent group of salps (Salpa aspera, Salpa fusiformis, Thalia democratica, Ritteriella picteti, Iasis zonaria) was observed throughout the study period. The cool-phase species tend to be distributed in mid-latitudes, while the distributions of the persistent species extend to equatorial waters. The cool-phase species have been reported to show little evidence of diel vertical migration, while most of the persistent species are reported to be diel migrants. No distinct multi-decadal patterns were observed in the dominant doliolid Dolioletta gegenbauri, but the rarer subtropical doliolid Doliolum denticulatum was present predominantly during the warm phase of the California Current. The recurrence patterns and biogeographic distributions of both salps and doliolids suggest that the warm phase of the California Current was accompanied by at least some intervals of anomalous transport "seeding" organisms from the south. Variations in total pyrosome and total appendicularian carbon biomass are not clearly related to long-term trends in the water column, although the highest pyrosome biomass occurred in earlier decades and appendicularian biomass has increased since 1999. Long-term changes in the biomass of pelagic tunicates appear to be chiefly responsible for the previously documented long-term decline in California Current total zooplankton biomass. The pattern of decline appeared to reverse in 1999, with a shift to cooler temperatures, somewhat reduced thermal stratification, and an increase in biomass of total zooplankton and of pelagic tunicates. © 2003 Elsevier Ltd. All rights reserved.