Influence of Salinity, Sulfate, and Fluoride on Growth of Golden Alga

Prymnesium parvum (golden alga) is a toxigenic harmful alga native to marine/estuarine habitats that has recently invaded inland brackish waters, causing severe ecological damage. A recent study of the Pecos River reported the unexpected finding of an upper salinity limit of ~20 ppt for golden alga presence, and other field studies reported positive associations with sulfates and fluoride. The objective of this study is to experimentally characterize the influence of salinity (NaCl, 5-30 ppt), sulfate (nominal 0-1000 mg/mL), and fluoride (NaF, nominal 0-125 mg/L) on golden alga growth. Culture conditions included 22°C, 12L: 12D, 3 replicates/treatment, 2 independent tests. Stationary (maximum) cell densities were achieved at 21-24 days. Maximum cell densities increased as salinity increased from 5 to 15 ppt, but decreased at higher levels. At constant salinity (5 ppt), cell densities were positively associated with sulfate concentration. While cell density decreased in the presence of fluoride, concentrations tested were above environmental levels. Our laboratory results with salinity and sulfate are consistent with field observations and provide evidence of causality. This information may be useful to inform management strategies based on water quality indices to curb the incidence and prevent the further spread of toxic blooms of golden alga.