Pseudo-nitzschia australis Frenguelli and related species from the west coast of the USA: Occurrence and domoic acid production

Awareness of the threat of the phycotoxin domoic acid, the cause of Amnesic Shellfish Poisoning (ASP), reached the U.S.A. west coast in the fall of 1991. Domoic acid in razor clams, mussels, and Dungeness crabs led to the closure of fisheries along the coasts of California, Oregon, and Washington. The death of pelicans that had fed on contaminated anchovies in Monterey Bay, California, set off the alarm by mid-September. The diatom Pseudonitzschia australis Frenguelli, detected in high concentrations in Monterey Bay at that time, was found to be a source of domoic acid. The present survey shows that, during the fall of 1991, P. australis and other Pseudonitzschia spp. were also observed in other sites on the west coast from Southern California to the mouth of the Columbia River (Newport, Coos Bay, and Ilwaco). In the fall of 1992, besides P. australis, other Pseudonitzschia spp. were present in Monterey Bay: P. americana and P. pungens, along with the known domoic acid producers P. delicatissima, P. pungens f. multiseries, and P. pseudodelicatissima. There was no report of a domoid acid outbreak in the Bay in 1992. There is strong evidence from the literature that, except for P. americana, all Pseudonitzschia species found in 1991 and 1992 have been part of the diatom community of the U.S.A. west coast at least since the 1940’s. The study of their distributional patterns can provide a predictive tool for the future onset of potential harmful blooms, and hence help protect the consumer and the seafood industry. Clones of P. australis from Monterey Bay, Coos Bay and Ilwaco were established in 1991, and clones of P. australis, P. americana, P. delicatissima, P. pungens, and P. pungens f. multiseries from Monterey Bay were established in 1992. Domoic acid was detected in P. australis (0.02-0.4 pg . cell-1) and in P. pungens f. multiseries (0.06-1.5 pg . cell-1) while P. americana, P. delicatissima, and P. pungens tested negative. The low toxicity found for these Pseudonitzschia clones may be attributed to testing the cell contents only and to growth and harvesting conditions in the lab. The implications of background levels of domoic acid to shellfish contamination in the field and, therefore, to long-term exposure of low concentrations of this toxin to consumers have yet to be explored.