Effects of salinity and temperature on phytoplankton community of San Francisco Estuary

Increases in water temperature and salinity that are predicted to occur with climate change are hypothesized to alter phytoplankton communities, expand cyanobacteria blooms, and alter food web structure in estuaries. For example, since 1999 blooms of the toxigenic cyanobacterium Microcystis aeruginosa have been observed in the California Delta (Delta), and appear to be linked to increased water temperature. The goal of this study was to understand how variations in water temperature and salinity influence the community composition of estuarine phytoplankton using a series of bottle experiments conducted with field-collected phytoplankton from the Delta. Based upon analysis of phytoplankton accessory pigments diagnostic of major algal groups (i.e., diatoms, cryptophytes, chlorophytes and cyanobacteria), all phytoplankton-group growth responded positively to elevated water temperature with cyanobacteria showing the largest positive response. Salinity optima were apparent at salinities 6 -8ppt for diatoms and <8ppt for cryptophytes while cyanobacteria showed little response to the salinities tested. Warm temperatures will promote cyanobacteria in fresh waters and coupled with its relative tolerance for salty conditions means that their distribution may spread into brackish water.