Seasonal Changes in Physical Processes in Regions I-IV Region I Region II Region III Region IV Biological Provinces Phytoplankton Provinces Zooplankton Provinces Invertebrate Benthos Provinces Marine Fish Provinces Bird Provinces El Nino Effects on Zoogeographic Boundaries Biophysical Interactions Overview of Biophysical Interactions Biophysical Interactions Involving Phytoplankton Biophysical Interactions Involving Zooplankton Biophysical Interactions Involving Benthic Invertebrates Biophysical Interactions Involving Marine Fish and Shellfish Biophysical Interactions Involving Bird Populations Summary of Biophysical Interactions-Hypothesis Formulation Historical Variability in the CCS The Last 100 Years The Last 1500 Years Global Eastern Boundary CurrentsThis section provides a detailed exposition of physical and biological aspects of the California Current ecosystem, building on information provided in Section III. Topics treated include seasonal variations in physical processes, zoogeographic boundaries, biophysical interactions, long-term variability as gleaned from paleoceanographic records, and a brief comparison of processes and species interactions in other eastern boundary current systems.