Many laboratories have solely used the Wilson isolate to physiologically characterize the harmful algal bloom (HAB) dinoflagellate Karenia brevis (C. C. Davis) G. Hansen et Moestrup. However, analysis of one isolate may lead to misinterpretations when extrapolating measurements to field populations. In this study, pulse-amplitude-modulated chlorophyll fluorometer (PAM-FL) relative electron transport rate (ETR), F v ⁄ F m , and chl were compared with traditional techniques, such as 14 C photosynthesis versus irradiance (P-E) curves, DCMU [3-(3¢,4¢-dichlorophenyl)-1,1-dimethyl urea] F v ⁄ F m , and extracted chl. The DCMU and PAM-FL values of F v ⁄ F m (r 2 = 0.51) and chl (r 2 = 0.58) were in good agreement. There was no correlation between 14 C and PAM-FL a, P max , and b parameters because PAM-FL ETR was only a relative measurement. The PAM-FL techniques were then used to investigate P-E curves, quantum yield of PSII (F v ⁄ F m ), and chl from 10 K. brevis isolates to determine whether one or all isolates would better represent the species. Comparisons were made with a radial photosynthetron, which allowed for controlled conditions of light and temperature. Isolate a, P max , and b varied between 0.097 and 0.204 lmol e ) AE m )2 AE s )1 AE (lmolquanta AE m )2 AE s )1 ) )1 , 80.41 and 241 lmol e ) AE m )2 AE s )1 , and 0.005 and 0.160 lmol e ) AE m )2 AE s )1 AE (lmol quanta AE m )2 AE s )1 ) )1 , respectively. Either carbon limitation and ⁄ or bacterial negative feedback were implicated as the cause of the P-E parameter variability. Furthermore, these results directly contradicted some literature suggestions that K. brevis is a low-lightadapted dinoflagellate. Results showed that K. brevis was more than capable of utilizing and surviving in light conditions that may be present on cloudless days off Florida.

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The internal lipid, carotenoid, and toxin concentrations of Karenia brevis (C. , <5 lM NO 3 ) mesocosms. Reverse-phase HPLC quantified the epoxidation state (EPS) of the xanthophyll-cycle pigments diadinoxanthin and diatoxanthin, and a Chromarod Iatroscan thin layer chromatography ⁄ flame ionization detection (TLC ⁄ FID) system quantified changes in lipid class concentrations. EPS did not exceed 0.20 in the low-light mesocosm, but increased to 0.65 in the high-light mesocosms. Triacylglycerol and monogalactosyldiacylglycerol (MGDG) were the largest lipid classes consisting of 9.3% to 48.7% and 37.3% to 69.7% of total lipid, respectively. Both lipid classes also experienced the greatest concentration changes in high-light experiments. K. brevis increased EPS and toxin concentrations while decreasing its lipid concentrations under high light. K. brevis may mobilize its toxins into the surrounding environment by reducing lipid concentrations, such as sterols, limiting competition, or toxins are released because lipids are decreased in high light, reducing any protective mechanism against their own toxins.C

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