Fig. 1. Illustrates that one group of copepods (Calanus pacificus and Metridia pacifica) decreased in abundance in most years in the 1990's in comparison with the 1950's, while another group increased during the same time period. (Anomalies from the mean of the 1950's and 1990's.)
Fig. 2. Illustrates that the first group of copepods shows a negative relationship with temperature (averaged over the upper 100 m, as residuals from the within-decade mean), while the other group shows no relationship with temperature anomalies.
Hyperiid amphipods (Bertha Lavaniegos [post-doc] and Mark Ohman)
Fig. 3. Upper panel illustrates that hyperiid abundances in the 1950's - early 1970's were twice hyperiid abundances from late 1970's to 1998. Lower panel illustrates that hyperiid species diversity was relatively high in the 1950's to early 1970's, and low in most of the 1980's and 1990's. [62 hyperiid species identified to date.] Some of the gelatinous hosts of the hyperiids, particularly doliolids, appear to have declined over the same time period.
With further analyses we expect to pin down whether the changes in zooplankton abundance and species diversity are associated with Regime Shifts or other low frequency physical changes in the CCS. We also expect to fully resolve the El Nino signals. The results to date illustrate that there has not been a unidirectional decline of all zooplankton in the CCS over the past 5 decades, but rather differential shifts among species: some taxa have increased, others decreased, others are essentially unchanged. The structure of the assemblages, and patterns of diversity, are not constant on decadal time scales and appear to respond to the large climate signals in the water column.