Effects of salinity, light and inorganic nitrogen on growth and toxigenicity of the marine dinoflagellate Alexandrium tamarense from northeastern Canada

Growth and toxin production of a highly toxic clone of the marinedinoflagellate Alexandrium tamarense, isolated fromthe lower St Lawrence estuary (Quebec) in eastern Canada, were studied inunialgal batch cultures under different conditions. Controlled experimentswere conducted on the production of paralytic shellfish poisoning (PSP)toxins under conditions of varying light (40, 60, 150, 230 and 470 mol m^-21s^-1), salinity (10, 15, 20, 25 and 30)and nitrate concentrations (0, 88, 364, 528 and 880 moll^-1). The effects of variable environmental factorson both toxin composition (% molar) and cell toxicity [pg STXeq (saxitoxinequivalents) cell^-1] were determined through theculture cycle. The toxin profile (% molar; mean SD), determined by high-performance liquidchromatography with fluorescence detection (HPLC-FD), remained stable andwas consistently dominated by the low-potencyN-sulfocarbamoyl toxins C1/C2 (64.0 ± 3%).There were also substantial relative amounts of the high-toxicity carbamatederivatives gonyautoxin 1-4 (GTX1-4) (1.7 ± 0.5%), neosaxitoxin(NEO) (16.2 ± 2%) ans saxitoxin (STX) (17.8 ± 2%).The cellular toxicity (mean ± SD: 58.8 ± 7 pg STXeqcell^-1) was essentially independent of light,salinity and nitrate concentration throughout the exponential growth phase,but varied over the growth stages in cultures. A positive correlation wasobserved between cellular toxicity and salinity-dependent growth rate,indicating that cell toxin quota may be affected by extrinsic factors, butit is not always a direct functional response to specific environmentalstress.