IDENTIFICATION AND ASSESSMENT OF DOMOIC ACID PRODUCTION IN OCEANIC PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE) FROM IRON‐LIMITED WATERS IN THE NORTHEAST SUBARCTIC PACIFIC¹

Abstract

We identified and investigated the potential toxicity of oceanic Pseudo-nitzschia species from Ocean Station Papa (OSP), located in a high-nitrate, low-chlorophyll (HNLC) region of the northeast (NE) subarctic Pacific Ocean. Despite their relatively low abundances in the indigenous phytoplankton assemblage, Pseudo-nitzschia species richness is high. The morphometric characteristics of five oceanic Pseudo-nitzschia isolates from at least four species are described using SEM and TEM. The species identified are Pseudo-nitzschia dolorosa Lundholm et Moestrup, P. granii Hasle, P. heimii Manguin, and P. cf. turgidula (Hust.) Hasle. Additional support for the taxonomic classifications based on frustule morphology is provided through the sequencing of the internal transcribed spacer 1 (ITS1) rDNA. Pseudo-nitzschia species identification was also assessed by the construction of ITS1 clone libraries and using automated ribosomal intergenic spacer analysis (ARISA) for environmental samples collected during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES), conducted in close proximity to OSP in July of 2002. Based on ITS1 sequences, the presence of P. granii, P. heimii, P. cf. turgidula, and at least five other putative, unidentified Pseudo-nitzschia ITS1 variants was confirmed within iron-enriched phytoplankton assemblages at OSP. None of the oceanic isolates produced detectable levels of particulate domoic acid (DA) when in prolonged stationary phase due to silicic acid starvation. The lack of detectable concentrations of DA suggests that either these strains produce very little or no toxin, or that the physiological conditions required to promote particulate DA production were not met and thus differ from their coastal, toxigenic congeners.

Unveiling a phytoplankton hotspot at a narrow boundary between coastal and offshore waters

“…3A), consistent with previous observations in the Northeast Pacific Ocean (32). The species composition of the pennate diatom Pseudo-nitzschia that dominated the nanoplankton 2 population at Station Papa after addition of iron was similar to Pseudo-nitzschia species composition at stations P2 and P4 in the transition zone, including the species Pseudonitzschia granii, which is classified as primarily oceanic (33) (Fig. 3 B and C).…”

Species occurrence of the potentially toxigenic diatom genus Pseudo-nitzschia and the associated neurotoxin domoic acid in the Argentine Sea

“…Both species can be mainly differentiated by examination of the number of striae and fibulae, which usually requires analysis by electron microscopy. Besides its original description, which confirmed its occurrence in Europe and Monterey Bay, California (Lundholm et al, 2006), it was also mentioned in a few studies carried out in the Drake Passage (Ferrario et al, 2004), northeast subarctic Pacific (Marchetti et al, 2008), the coasts of Portugal (Churro et al, 2009) and Malaysian Borneo (Lim et al, 2012a). In our study, it was confined to northern shelf-break waters sampled during spring, with temperatures of 8.1-9.7 C and salinities from 33.7 to 33.9.…”

“…Toxigenic Pseudo-nitzschia species are typically found in coastal waters, whereas open-ocean strains are usually found to be nontoxigenic or producers of only very low DA cell concentrations (Marchetti et al, 2008;Trick et al, 2010). Nevertheless, it is unclear if this tendency reflects genetic distinctiveness ("ecotypes") or is largely a function of ambient environmental influences on toxin production.…”

Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health

“…While it is generally considered that natural oceanic Pseudo-nitzschia populations do not produce DA, or only at very low levels (in the range of fg DA cell À1 or pg DA l À1 ) (Marchetti et al, 2004(Marchetti et al, , 2006(Marchetti et al, , 2008, the mesoscale iron-fertilization experiments (cf. reviews by de Baar et al, 2005;Boyd et al, 2007), starting in the 1990s, have provided some opportunist information on both Pseudo-nitzschia competition and DA production.…”

“…The most frequently detected species within the clone library was P. pungens, which also had the greatest number of distinct genotypes (12). Marchetti et al (2008) used the ARISA to identify Pseudonitzschia species during an iron enrichment experiment in the northeast subarctic Pacific Ocean, near Ocean Station Papa. They compared the results from the ARISA (performed on bulk seawater samples) to clone libraries developed from the same samples.…”