Effects of temperature, irradiance, and salinity on photosynthesis, growth rates, total toxicity, and toxin composition for Alexandrium fundyense isolates from the Gulf of Maine and Bay of Fundy

The objective of this study was to determine the effects of temperature, irradiance, and salinity on photosynthesis, growth rate, total toxicity, and toxin composition for two Alexandrium fundyense isolates in the laboratory. The A. fundyense cultures studied were isolated from coastal waters off Monhegan Island (MI) in the GoM and the Bay of Fundy (BoF). Laboratory experiments demonstrated that temperature exerted the greatest impact on chlorophyll-specific maximal photosynthetic rates with negligible effects by light or salinity. Temperature and irradiance exerted the greatest influence on species-specific growth rates, with the MI isolate exhibiting greater maximal growth rates. The BoF isolate was generally more toxic, with temperature inducing the greatest change in cellular toxicity, followed by irradiance and salinity. Variations in toxicity were due to changes in toxin concentration, the relative toxin composition, or both depending on the isolate and experimental condition. The lack of a clear relationship between photosynthesis or growth and toxicity suggests that toxicity is, at least in part, driven directly by environmental conditions. Isolate-specific A. fundyense responses to the environment incorporated into modeling efforts may ultimately enhance predictive and monitoring capabilities for PSP outbreaks.