PHYTOPLANKTON SPECIES IN THE CALIFORNIA CURRENT SYSTEM OFF SOUTHERN CALIFORNIA: THE SPATIAL DIMENSIONS

This paper examines 16 years of microscopic information about phytoplankton taxonomic composition and abundances from each of four regions in the Cal-COFI area. The NE region is approximately the region of the Southern California Bight; the SE region is the lower edge of the bight; the Offshore is the westernmost region; and the Alley is the path between the NE and the Offshore through which the California Current meanders. The NE region and the Alley consistently had the highest phytoplankton abundances, dominated by diatoms. These two areas were most similar with respect to abundance fluctuations and species composition. The Offshore had the lowest abundances, dominated by coccolithophores. The SE region was intermediate with respect to both abundance and composition. Temporal patterns of abundance and composition differed among regions. An increase in phytoplankton abundance was centered in the Offshore region, but was not accompanied by a change in phytoplankton composition. The only detectable effect of the ENSO cycle on phytoplankton abundance was an increase in abundance during La Nina events in the Offshore. However, a cycle of Offshore species composition with a period of five to eight years did not appear to be related to ENSO. Seasonal cycles were strongest in the NE and Alley. In both these regions, high abundances in spring during the early years of this study decreased and the annual abundance maximum appeared to migrate to summer and fall. These shifts may have been driven by decreases in the abundances of the diatom phytoplankton in the spring or by an interaction between the present cruise schedule and a gradual delay in the spring bloom.