Variability of Pseudo-nitzschia and domoic acid in the Juan de Fuca eddy region and its adjacent shelves

The Juan de Fuca eddy is a toxic hot spot. Domoic acid (DA) was detected in the eddy during each of six cruises over a 4-yr study, although Pseudo-nitzschia abundance and toxin concentrations were highly variable. During the September 2004 eddy bloom, Pseudo-nitzschia spp. exceeded 13 X 10(6) cells L-1, and particulate DA reached 80 nmol L-1. Of the >10 species of Pseudo-nitzschia identified in this region, those coincident with the most toxic blooms are P. cf. pseudodelicatissima, P. cuspidata, P. multiseries, and P. australis. However, the presence of any particular species could not be used as an indicator of toxicity because of the high level of variability in intracellular DA in field assemblages. Pseudo-nitzschia cells were typically associated with blooms of other diatom taxa but also were coincident with blooms of euglenoids and dinoflagellates in the eddy region. Pseudo-nitzschia always comprised <17% of the total carbon biomass, thereby rendering remote sensing an unsuitable means for predicting toxigenic Pseudo-nitzschia blooms in this region. Our results support the hypothesis that the Juan de Fuca eddy region and not the nearshore zone is the primary initiation site for toxic blooms of Pseudo-nitzschia affecting the Washington coast. Although particulate DA was observed near the edges of the Columbia River plume, whether toxin can be produced in situ in plume water is not resolved. No first-order predictive relationships were found for either Pseudo-nitzschia abundance or DA concentration and environmental data from all six cruises.