This report reviews and provides a preliminary interpretation of recent observations made by CalCOFI (California Cooperative Oceanic Fisheries Investigations) and other programs sampling the coastal waters of the Californias. Since this is a continuation of a series of annual reports, the emphasis here is upon observations made during the past 18 months, but longer-term trends must also be considered. The major change in oceanographic structure in the past year was the transition from strong El Niiio conditions in early 1998 to cool-water, La Nilia conditions in early 1999. Ecosystem structure also showed large changes during this period. Phytoplankton abundance during 1998, as indlcated by chlorophyll concentration, was typical of the values seen during the last decade, but it appeared to be increasing in early 1999 in association with the transition to cool-water conhtions. Macrozooplankton biomass during 1998 continued the long-term trend of low values which have been seen since the mid-1970s regime shift, and El Niiio-related changes were superimposed upon t h s trend. The 1999 macrozooplankton data are not yet available to assess whether biomass is increasing. Observations made at coastal shore stations, in southern California kelp forest communities, in central and northern California, and in Baja California, Mexico, are considered in order to place the CalCOFI observations in a larger regional context. Because this year marks the fiftieth anDAVID M. CHECKLEY Marine Life Research Group Scripps Institution of Oceanography University of California, San Diego 9500 Gilman Drive La Jolla, California 92093-0227 K. DAVID HYKENUACH, ARNOLD W. MANTYLA, MICHAEL M. MULLIN Marine Life Research Group Scripps Institution of Oceanography University of California, San Diego 9500 Gilnian Drive La Jolla, California 92093-0227