Parallel Analyses of Alexandrium catenella Cell Concentrations and Shellfish Toxicity in the Puget Sound

Abstract

Alexandrium catenella is widespread in western North America and produces a suite of potent neurotoxins that cause paralytic shellfish poisoning (PSP) in humans and have deleterious impacts on public health and economic resources. There are seasonal PSP-related closures of recreational and commercial shellfisheries in the Puget Sound, but the factors that influence cell distribution, abundance, and relationship to paralytic shellfish toxins (PSTs) in this system are poorly described. Here, a quantitative PCR assay was used to detect A. catenella cells in parallel with state shellfish toxicity testing during the 2006 bloom season at 41 sites from April through October. Over 500,000 A. catenella cells liter ؊1 were detected at several stations, with two main pulses of cells driving cell distribution, one in June and the other in August. PSTs over the closure limit of 80 g of PST 100 per g of shellfish tissue were detected at 26 of the 41 sites. Comparison of cell numbers and PST data shows that shellfish toxicity is preceded by an increase in A. catenella cells in 71% of cases. However, cells were also observed in the absence of PSTs in shellfish, highlighting the complex relationship between A. catenella and the resulting shellfish toxicity. These data provide important information on the dynamics of A. catenella cells in the Puget Sound and are a first step toward assessing the utility of plankton monitoring to augment shellfish toxicity testing in this system.

Examination of the Seasonal Dynamics of the Toxic Dinoflagellate Alexandrium catenella at Redondo Beach, California, by Quantitative PCR

“…Similarly, the 3-year survey in Monterey Bay noted that 20% of samples that were positive for A. catenella (abundances of Ͻ1,000 cells liter Ϫ1 ) had no measurable particulate STX (37). Similar results were obtained in Puget Sound, where almost one-third of the stations revealed no shellfish toxicity despite the presence of A. catenella in surface waters (16). The authors of the latter study concluded that the use of absolute cell numbers as an indicator of STXeq levels in shellfish was inappropriate for Puget Sound (16).…”

“…A. catenella cells were detected more frequently in Monterey Bay (55% of samples) (37) than in King Harbor (17% of samples). Further north, in Puget Sound, cell abundances ranged from 5 to 812,500 cells liter Ϫ1 from late April through October 2006 (16). The maximal abundances greatly exceeded the maximal abundance observed during our 4-year survey.…”

“…This includes nonspecific reaction products or primer dimers, which may generate false-positive signals. Although a recently developed SYBR-based qPCR assay by Dyhrman et al was found to be an efficient tool to monitor A. catenella in Puget Sound (16), the same approach would have likely failed to detect A. catenella strains from King Harbor due to mismatches between their forward primer and our D1-D2 sequences, even though the primer was designed to target the North American ribotype. This finding serves as an important reminder that genomic variability in geographically distinct strains of the same species needs to be considered and that probes and primers can be effective only if the taxonomic information on which identifications are based is sound.…”

“…fundyense clade. While A. catenella was the only morphotype identified from Redondo Beach samples and is, to date, the only Alexandrium species documented on the U.S. west coast (10,16,37), new insight into species distinctions based on sequence information may lead to reevaluation of geographical distributions. In any case, the detection of all toxic Alexandrium species within group I can be revealed by our qPCR approach, which is of ecological relevance for HAB monitoring and early warning of PSP events.…”

“…High concentrations of paralytic shellfish toxins in U.S. waters have been particularly frequent and acute off the northeastern U.S. coast, where most studies of Alexandrium bloom dynamics and toxin production have been conducted (5,15,17,49,52,77). However, PSTs have also been reported routinely along the entire west coast of the United States (16,37,38,(41)(42)(43)(44)(45)(46)(47)56) and in other coastal locations throughout the world (http://www.whoi.edu/redtide/page.do?pidϭ14899).…”