Journal of Plankton Research, Vol 21, 939-955, Copyright © 1999 by Oxford University Press
J Parkhill and A Cembella
Growth and toxin production of a highly toxic clone of the marine
dinoflagellate Alexandrium tamarense, isolated from
the lower St Lawrence estuary (Quebec) in eastern Canada, were studied in
unialgal batch cultures under different conditions. Controlled experiments
were conducted on the production of paralytic shellfish poisoning (PSP)
toxins under conditions of varying light (40, 60, 150, 230 and 470
ORIGINAL ARTICLES
Effects of salinity, light and inorganic nitrogen on growth and toxigenicity of the marine dinoflagellate Alexandrium tamarense from northeastern Canada
Center for Environmental Observation Technology and Research, Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada; Institute for Marine Biosciences, National Research Council, 1411 Oxford Street, Halifax, Nova Scotia, B3H 3Z1, Canada; Corresponding author
mol m-21
s-1), salinity (10, 15, 20, 25 and 30
)
and nitrate concentrations (0, 88, 364, 528 and 880 
mol
l-1). The effects of variable environmental factors
on both toxin composition (% molar) and cell toxicity [pg STXeq (saxitoxin
equivalents) cell-1] were determined through the
culture cycle. The toxin profile (% molar; mean 
SD), determined by high-performance liquid
chromatography with fluorescence detection (HPLC-FD), remained stable and
was consistently dominated by the low-potency
N-sulfocarbamoyl toxins C1/C2 (64.0 ± 3%).
There were also substantial relative amounts of the high-toxicity carbamate
derivatives 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 STXeq
cell-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 was
observed between cellular toxicity and salinity-dependent growth rate,
indicating that cell toxin quota may be affected by extrinsic factors, but
it is not always a direct functional response to specific environmental
stress.
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