Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.

A study of 25 cultures tentatively identified as Pseudo-nitzschia delicatissima (Cleve) Heiden, and originating from geographically widely distributed locations, showed both morphological and genetic variation among strains. Use of rRNA-targeted DNA probes on 17 different strains showed large variation in the hybridization patterns. Detailed morphological studies placed the isolates into three groups. The sample on which the neotype of P. delicatissima is based was also examined, and used to establish the morphological identity of P. delicatissima. Phylogenetic analyses of 16 strains, based on sequences of internal transcriber spacer 1 (ITS1), 5.8S and ITS2 of the nuclear-encoded rDNA, supported the morphological observations and the hybridization studies, and revealed large genetic variation among strains. A combination of the morphological and molecular findings resulted in the description of two new species, P. decipiens sp. nov. and P. dolorosa sp. nov. P. dolorosa has a mixture of one or two rows of poroids in the striae whereas P. delicatissima always has two rows. In addition, P. dolorosa has wider valves and a lower density of poroids. P. decipiens differs from P. delicatissima by a higher density of striae on the valve face as well as a higher density of poroids on the girdle bands. Among the strains referred to P. delicatissima, an epitype was selected. Large genetic variation was found among the P. delicatissima strains and a subdivision into two major clades represent cryptic species.

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Efforts to understand the ecologic and environmental parameters that govern harmful algal blooms (HABs) require rapid and specific identification of causative species. Traditional methods of species identification using light and electron microscopy are useful in this regard but are also time consuming, making routine analysis of a large number of samples difficult. Techniques that speed and ease the detection of HAB species as they occur in natural populations are therefore desirable. In this paper, we continue efforts to develop species-specific large subunit ribosomal RNA (LSU rRNA)-targeted fluorescent DNA probes for a variety of Pseudo-nitzschia H. Peragallo species, a group of marine pennate diatoms that includes representatives linked to production of domoic acid and amnesic shellfish poisoning (ASP). A custom filter tube and filtration manifold that has utility for both whole cell (in situ) hybridization as well as preparing samples for scanning electron microscopy (SEM) is described. Filter-based whole cell hybridization was used to identify a variety of newly isolated Pseudo-nitzschia clones, and probe results were confirmed using SEM. Some isolates of P. pungens (Grunow) Hasle exhibited variable (intraclonal) reactivity toward the P. pungens-specific probe. Three isolates of P. subpacifica (Hasle) Hasle were found to cross-react with probes designed for P. fraudulenta (Cleve) Hasle and P. heimii Manguin. Four isolates did not react with any species-specific probes; this group comprised three distinct morphotypes whose fine-scale morphologic features did not agree with published descriptions of Pseudo-nitzschia species. Evaluation of the filter method using cultured cells added to natural (whole water) samples indicated quantitative recovery of target species. Confirming results of probe assays using SEM was difficult when the target species was less than 10 4 cells·L Ϫ1 in the presence of greater than 10 6 cells·L Ϫ1 of other nontarget diatom species. A variety of Pseudo-nitzschia, including P. australis Frenguelli, P. fraudulenta, P. heimii, P. pseudodelicatissima (Hasle) Hasle, P. pungens, P. multiseries (Hasle) Hasle, and Nitzschia americana Hasle, were identified using whole cell hybridization in a variety of field samples containing mixed assemblages of plankton, and these results were confirmed using SEM. The filter tube method of applying probes was used onboard ship for near real-time identification and enumeration of a variety of Pseudonitzschia species.