An ecological study of a massive bloom of toxigenic Pseudo-nitzschia cuspidata off the Washington State coast

Trainer, Vera L., Mark L. Wells, William P. Cochlan, Charles G. Trick, Brian D. Bill, Keri A. Baugh, Benjamin F. Beall, Julian Herndon, Nina Lundholm

Limnol. Oceanogr., 54(5), 2009, 1461-1474 | DOI: 10.4319/lo.2009.54.5.1461

ABSTRACT: In September 2004 a large, nearly monospecific diatom bloom of Pseudo-nitzschia cuspidata off the coast of the state of Washington reached cell concentrations of 6.1 × 106 cells L-1 and produced maximum particulate domoic acid (pDA), dissolved domoic acid (dDA), and cellular domoic acid concentrations of 43 nmol L-11, 4 nmol L-1, and 63 pg cell-1, respectively. This bloom co-dominated the phytoplankton assemblage with the euglenoid Eutreptiella sp. in the Juan de Fuca eddy region, a known initiation site for toxigenic Pseudo-nitzschia blooms. Two isolates of P. cuspidata collected during separate cruises produced domoic acid (DA) in culture. During the September 2004 survey, 84% of the stations (n = 98) had detectable Pseudo-nitzschia and 78% had detectable pDA. There were no significant correlations between either pDA or cellular DA and ambient concentrations of macronutrients; however, when considering only those stations where Pseudo-nitzschia was present, pDA was positively correlated with chlorophyll a and negatively correlated with temperature (p < 0.01) at both 1- and 5-m depths. Correlations between cellular DA concentrations and total bacteria or cyanobacteria abundances were not significant. Variable ratios of pDA:dDA in the eddy region suggest that DA release was under cellular regulation by Pseudo-nitzschia. Stations where dissolved Fe concentrations were limiting (,0.5 nmol L-1) had the highest Pseudo-nitzschia abundances and pDA and cellular DA values. These results provide enticing field evidence of the role of Fe limitation in controlling cellular DA levels.

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