MORPHOLOGICAL,TOXICOLOGICAL, AND GENETIC DIFFERENCES AMONG PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE) SPECIES IN INLAND EMBAYMENTS AND OUTER COASTAL WATERS OF WASHINGTON STATE,USA1

Plankton samples from three inland embayments and several outer coastal sites of Washington State were collected from 1997 through 1999 and were examined for the presence of diatoms of the genus Pseudo‐nitzschia and levels of the toxin, domoic acid (DA). Seven species were observed, including Pseudo‐nitzschia pungens (Grunow ex Cleve) Hasle, P. multiseries (Hasle) Hasle, P. australis Frenguelli, P. fraudulenta (Cleve) Hasle, P. cf. heimii Manguim, P. pseudodelicatissima (Hasle) Hasle, and P. delicatissima (Cleve) Heiden. The coastal Pseudo‐nitzschia species assemblages differed significantly from those observed within embayments. The dominant species observed at coastal sites were P. pseudodelicatissima and P. cf. heimii. Pseudo‐nitzschia assemblages found in embayments included one or more of the following species: P. pungens, P. multiseries, P. australis, P. pseudodelicatissima, and P. fraudulenta. The nuclear large subunit rRNA gene was sequenced for six of the seven species identified. This sequence revealed that P. multiseries, P. pungens, P. australis, and P. heimii were genetically similar to those found in California, whereas P. delicatissima and P. pseudodelicatissima were distinct from the California isolates. Although the concentrations of DA in razor clams along Washington State coasts have exceeded regulatory limits several times since 1991, levels of DA in shellfish from Washington State embayments have not yet exceeded regulatory limits. The widespread presence of toxin‐producing Pseudo‐nitzschia species suggests, however, that toxic blooms are likely to occur within embayments in the future. In conjunction with the monitoring of environmental conditions conducive to toxic bloom formation, the development of species‐specific probes for rapid and accurate detection of potentially toxic Pseudo‐nitzschia species in this region would enable the forecasting of a toxic event before DA accumulates in shellfish, thereby reducing the impacts to coastal communities.