Pseudo-nitzschia species (Bacillariophyceae) in Louisiana coastal waters: Molecular probe field trials, genetic variability, and domoic acid analyses

An 18-month field survey of the Pseudo-nitzschia population present in Loui siana coastal waters was conducted comparing species abundance estimates by novel fluorescent molecular probes (16S large subunit rDNA oligonucleotide sequences) with traditional electron and differential-interference light m icroscopy, While the probe and microscopic analyses agreed on the presence or absence of four common Pseudo-nitzschia species (P, multiseries (Hasle) Hasle, P, pseudodelicatissima (Hasle) Hasle, P, delicatissima (P.T. Cleve) Heiden, and P. pungens (Grunow) Hasle in 66% of the samples analyzed, the p robes gave conflicting results with the microscopic methods in the remainin g 34% of the samples. The majority of the discrepancies appear to be becaus e of genetic variation within the Pseudo-nitzschia population, especially i n P. pseudodelicatissima, indicating that the Monterey Bay Pseudo-nitzschia spp, may not be appropriate reference strains for distinguishing Louisiana Pseudo-nitzschia spp. Additionally, P, pseudodelicatissima has been associ ated with domoic acid (DA) activity in three field samples, at levels up to 22 times higher than the highest value given in other published reports of DA production by this species. The contemporaneous existence of multiple s trains of P. pseudodelicatissima (toxic and nontoxic) presents new challeng es to the study of the ecophysiology and population dynamics of this bloom- forming species.