Estimates of specific toxicity in several Pseudo-nitzschia species based on culture and field studies

Keri A. Baugh, Jeannie M. Bush, Brian D. Bill, Kathi A. Lefebvre and Vera L. Trainer

NOAA Fisheries, Marine Biotoxin Program, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, Washington, 98112, USA, keri.baugh@noaa.gov

Determining which species of Pseudo-nitzschia produce and release domoic acid (DA) under varied environmental conditions is one of the challenges of the ECOHAB-Pacific Northwest project. To gain an understanding of the species of Pseudo-nitzschia that are the major toxin producers, representative isolates from the ECOHAB study site were grown as clonal cultures. Both particulate and dissolved DA were measured at various stages of growth using a receptor-binding assay and an enzyme-linked immunosorbent assay, respectively, and compared to toxin data obtained during a September 2003 cruise. A clonal P. multiseries culture isolated from a northern beach site contained the highest particulate DA (pDA) level of 70.4 nM and released the highest amount of dissolved DA (dDA) (>5 nM), illustrating the potential for this species to cause harm. A clonal P. australis isolate also produced relatively high levels of pDA and dDA, whereas P. delicatissima, P. pseudodelicatissima, P. pungens, and P. fraudulenta, produced low or undetectable levels of pDA and dDA. These culture studies suggest that the dDA levels of up to 17.6 nM measured during the September 2003 cruise were due to toxin produced and released primarily by P. australis cells. We estimate that the specific toxicity contributed by P. australis at a toxic "hot spot" off the Washington coast in mid-September 2003 reached a maximum of 94.4 pg/cell.