Co-occurrence of Pseudo-nitzschia species and the neurotoxin domoic acid in the Gulf of Maine during 2008 and 2010

Background/Question/Methods

Many species in the marine diatom genus Pseudo-nitzschia produce the neurotoxin domoic acid (DA), which can accumulate in shellfish and finfish and negatively impact human and wildlife health. In 2008, shellfish harvests in the Canadian waters of the Bay of Fundy were closed because of high DA concentrations, however, no closures have been reported yet in nearby US waters. In this study, the spatial and temporal variability of DA concentrations were investigated in the US coastal waters of the Gulf of Maine and the offshore waters of the highly productive Georges Bank region. Phytoplankton samples for particulate DA analysis and Pseudo-nitzschia identification were collected during monthly weeklong cruises (May-August) in 2008 and 2010. The molecular fingerprinting technique Automated Ribosomal Intergenic Spacer Analysis (ARISA) was used for Pseudo-nitzschia species identification. An Enzyme-Linked Immunosorbent Assay (ELISA) was used to measure particulate DA concentrations. Bivariate comparisons of environmental parameters (temperature, salinity, nutrient concentrations, transmissivity, chlorophyll a biomass), relative Pseudo-nitzschia abundance, and DA concentrations were conducted using Spearman correlation analysis. 

Results/Conclusions

Preliminary analysis of 26 samples from Georges Bank found all stations positive for DA, with the highest DA concentration (816.8 ng L^-1) observed at the crest of Georges Bank in 2008. Toxin concentrations were significantly and positively associated with light transmissivity (Spearman’s R=0.626, p<0.01). Although transmissivity was significantly and negatively correlated with other environmental parameters (p<0.01 for chlorophyll a, ammonium, phosphate, silicate:ammonium, and silicate:phosphate), none of these were similarly associated with DA concentrations. Regions of higher toxicity were dominated by either P. seriata or P. sp. “Hobart,” a sibling species or variant of P. pseudodelicatissima. Interestingly, DA was not correlated with either toxic species, but rather was negatively correlated with the relatively nontoxic species P. delicatissima (Spearman’s R=-0.603, p<0.01). We are evaluating additional samples to better characterize the ecological and environmental processes involved in DA production in the Gulf of Maine. These preliminary results suggest that Pseudo-nitzschia species composition could be a useful indicator, and perhaps predictor, of DA toxicity in the environment.