Estimates of specific toxicity in several Pseudo-nitzschia species from the Washington coast, based on culture and field studies

To gain an understanding of the species of Pseudonitzschiathat are the major toxin producers in the Pacific Northwest, representative isolates from the Ecology and Oceanography of Harmful Algal Blooms inthe Pacific Northwest (ECOHAB-PNW) study site were grown as clonal cultures. Both particulate and dissolved domoic acid (DA) were measured at various stages of growth using a receptor-binding assay and anenzyme-linked immunosorbent assay respectively, and compared to toxin data obtained during a cruise in September 2003. A clonal P. multiseries culture isolated from a northern beach site contained the highest particulate DA (pDA) level of 70.4nmol l–1 and released thehighest amount of dissolved DA (dDA, >5nmol l–1), illustratingthe potential for this species to cause harm. A clonal P. australis isolate also produced relatively high levels of pDA (3.2nmol l–1) and dDA (4.3nmol l–1), whereas P. delicatissima, P. cf. pseudodelicatissima, P.pungens and P. fraudulenta produced low or undetectablelevels of pDA and dDA. These culture studies suggest that the dDA levels of up to 17.6nmol l–1 measured during September 2003 were owing to toxin produced and released primarily by P. australis cells. Itis estimated that the maximum specific toxicity reached by P. australis at a toxic ‘hot spot’ off the Washington coast in mid-September 2003 was 94.4pg cell–1