California Sea Grant College Program

Phytoplankton samples were collected off the Monterey Municipal Wharf II at a single location (36º 36’ N and 121º 53’ W) weekly from June 2003 to March 2010. The contribution of five algal groups to total chlorophyll a (chl a) was derived using CHEMTAX from biomarker pigment measurements made via HPLC analysis. The purpose of this study was to specifically define the relative abundances of diatoms and dinoflagellates on a seasonal and interannual basis. Spearman’s rho (ρ) correlation coefficients were calculated to determine the strength of the relationship between the diatoms and dinoflagellates and two environmental variables; sea surface temperature (SST) and upwelling indices (UI). During the summer of 2004 and until the end of 2006, previous studies had suggested that the typical diatom-dominated bay shifted to a dinoflagellate-dominated system resulting from global warming effects on mixed layer stability. The high-resolution (weekly), long-term (2003-2010) sampling regime described in the current study coincided with this time frame and allowed a robust test of the tenet that “the age of dinoflagellates” had developed in Monterey Bay.Pigment analysis indicated that diatoms and dinoflagellates displayed interannual and seasonal variability, particularly during the anomalous oceanographic conditions from 2004-2006. Diatoms were most abundant during the upwelling season and displayed a significant and positive correlation to UI, while they exhibited no relationship with shifts in SST. The dinoflagellates revealed a consistent fall bloom each year, displayed a significantly positive correlation to increases in SST and a significantly negative correlation to UI. This data set proved to be a robust, unique collection that clearly captured the “age of dinoflagellates” and compared well with larger scale studies conducted off shore waters of Monterey Bay, indicating the value of high frequency shore station based monitoring for tracking major oceanographic features. In this study, however, it was shown that the dominant period of dinoflagellates was short-lived since diatoms returned to dominance in 2007.