GLOBEC 2000: Long-term Changes in California Current Zooplankton Assemblages and Euphausiid Population Dynamic Parameters

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The PIs will test the GLOBEC core hypothesis that production regimes in the Coastal Gulf of Alaska and Califomia Current System covary, and are coupled through atmospheric and oceanic forcing, through comparative analysis of zooplankton populations and measures of atmospheric and oceanic forcing in different regions of the NE Pacific. During a Phase 1 study, the PIs uncovered substantial changes in the California Current zooplankton (Region I) on interdecadal time scales (e.g., changes in salp and euphausiid regimes) as well as interannual time scales (e.g., El Nino-related changes in copepod diversity and zooplankton biomass). For Phase 2 , the PIs will focus on Region II of the CCS off central/northern California to determine whether the pronounced perturbations that they detected are spatially coherent in different regions of the CCS and are linked to zooplankton fluctuations elsewhere in the NE Pacific, specifically off Oregon and in the Coastal Gulf of Alaska. In addition, estimates of instantaneous, stage-specific mortality rates for euphausiid populations of the NE Pacific will be made using lipofuscin-based measures of euphausiid age and inverse modeling techniques. Long-term stability in food web structure also will be investigated using zooplankton stable isotopes.