UC San Diego

We investigated long-term changes in the abundance and species composition of hyperiid amphipods in the Southern California Bight and nearby waters from twelve springime CalCOFI cruises spanning the period 1951-1997. Sixty-two hyperiid species were detected in the study region. We found dimunition in species diversity and in total hyperiid abundance during the studied period. Despite high interannual variability, there was higher species richness, evenness of species numbers, and abundances of hyperiids in an earlier time period (1951 to 1972) and generally lower species richness, evenness, and abundances in a more recent time period (1979 to 1997). Variations in abundance of total hyperiids were significantly correlated with variations in abundance of presumed gelatinous zooplankton hosts, especially salps, physonect siphonophores, and pyrosomes. Species-specific correlations showed significant associations between ten species of hyperiids and different species of salps, siphonphores, and medusae. Some amphipods were correlated with more than one host. Hyperiid amphipod assemblages appear to be sensitive to large-scale climate changes in the NE Pacific, through either direct responses or indirectly through their association as parasitoids on gelatinous hosts.