The influence of climate on phytoplankton community biomass in San Francisco Bay Estuary

The distribution of biomass within the phytoplankton community in northern San Francisco Bay Estuary was influenced by environmental conditions resulting from an interdecadal climate regime shift between 1975 and 1993. A decrease in percentage of diatom biovolume characterized the period 1975-1989 and was caused by both a decrease in diatom and an increase in green and bluegreen algae and flagellate species biovolume. Among the diatoms, there was a greater loss of pennate than centric diatoms. The direct role of climate variation on phytoplankton community biovolume was determined using climatically-related environmental variation that was isolated from the total environmental variation using the covariance between a California climate index and a suite of physical and chemical variables and summarized by principal component analysis. Significant correlation between climatically-related environmental variation and phytoplankton species and species group biovolume suggested a link between climate and the distribution of biovolume in the phytoplankton community. Further analysis of the possible mechanisms controlling the association between climatically-related environmental variation and phytoplankton community biovolume confirmed the importance of water temperature, specific conductance, and water transparency to pennate diatom biovolume. Comparison of natural and anthropogenic processes indicated that diatom biovolume at each station was influenced by environmental conditions even though total diatom biovolume in the estuary was strongly influenced by water diversion.